Authors:
Petrescu L., Popa M., Radulian M.

Abstract:
The South-East Carpathians in Romania host the Vrancea Seismic Zone (VSZ), an intraplate seismic nest of frequent high magnitude earthquakes that cause unusually high damage over extended areas. Estimating the amplification of seismic signals strongly depends on the depth to the geophysical bedrock and the complex near surface geological structures. To improve seismic hazard estimates and ultimately mitigate seismic risk, we determine the frequency of resonance at 81 broadband seismic stations in southeast Romania using the horizontal-to-vertical spectral ratio (HVSR) of ambient seismic noise. We jointly invert HVSR functions with Rayleigh wave phase velocity dispersion curves using a Markov-chain Monte Carlo algorithm under the assumption of a diffuse field. Our results show excellent correlation between the fundamental frequency of resonance and local surface geology: stations located on foreland sedimentary basins show HVSR peaks in the range 0–1 Hz, while those located in orogenic nappes reach values as high as 10 Hz. Seismic bedrock topography mirrors the crystalline bedrock depth inferred from gravity modeling, but is consistently ∼2000 m shallower, corresponding to the interface between Paleozoic-Triassic to Jurassic-Cretaceous sedimentary levels on the Moesian Platform constrained by borehole data. The near surface seismic model shows anomalously low velocities in the Focsani forearc basin, adjacent to the VSZ, consistent with extremely low resonance frequencies and deep sedimentary layer successions (>5 km). In the back-arc of the Carpathian Orogen, at the contact with the Transylvanian Basin, average resonance frequencies are <2 Hz and inferred seismic bedrock depths vary laterally, likely affected by buried volcanic structures and diapiric salt domes. Our study presents the largest endeavor to study anomalous intensity patterns and local site effects in and around the VSZ and has fundamental implications for seismic risk evaluation and future civil engineering design planning.

Authors:
Toader V.E., Ionescu C., Moldovan I.A., Mărmureanu A., Brișan N.S., Lingvay A., Mihai A.

Abstract:
The analysis of the relationship between radon and seismicity was previously carried out in the seismic zone of Vrancea (Romania), positioning the measuring stations on tectonic faults. This article analyzed the evolution of radon under conditions of deep and surface seismicity and the presence of mud volcanoes, as well as fires caused by gasses emanating from the ground. The monitoring area was extended to the Black Sea and the area of the Făgăraș-Câmpulung fault, where a special radon detection system was established and proposed for patenting. The case study was the impact of the earthquakes in Turkey (7.8 R and 7.5 R on 6 February 2023) on the seismically active areas in Romania in terms of gas emissions (radon, CO2). The main analysis methods for radon (we also included CO2) were applied to integrated time series and the use of anomaly detection algorithms. Data analysis showed that the effects of global warming led to variations in seasonal gas emissions compared to previous years. This made it difficult to analyze the data and correlate it with seismicity. Several of the cases presented require more in-depth analysis to determine the cause of the unusually high radon levels. The primary purpose of establishing the monitoring network is to use the gas emissions as seismic precursors, but the measurements are affected by the conditions under which the monitoring is conducted. In some cases, we are dealing with the effects of pollution, and in other cases, more extensive studies are required. One solution we plan to use is to expand the measurement points to locate the source of the anomalies and use weather data to determine the impact of global warming on the measurements. The main conclusions related to the development of a radon monitoring network and, in general, to the emission of gasses in earthquake-prone areas relate to the importance of the choice of equipment, monitoring location, and installation method.

Authors:
Mihai A., Toader V.E., Moldovan I.A., Radulian M.

Abstract:
Understanding the seismo–ionospheric coupling mechanism requires a quiet geomagnetic condition, as this represents an ideal situation to detect abnormal variations in the geomagnetic field. In reality, continuous interactions between solar wind and Earth’s magnetosphere create many fluctuations in the geomagnetic field that are more related to sun–magnetosphere interactions than to seismotectonic causes. A triaxial magnetometer was installed at the Muntele Rosu Observatory near the Vrancea seismic zone in 1996 to measure the local magnetic field. Since 2002, the data have become more consistent, allowing for the representation of long time series. Since then, variations have been observed on the eastern component (By) of the magnetic field, which sometimes overlaps with significant earthquakes. Previous studies have shown that high decreases in amplitude recorded on the By component of the magnetic field measured at Muntele Rosu have been accompanied by higher seismicity, while small decreases have been accompanied by lower seismic energy release. This research analyzes the geomagnetic data collected between September 2002 and May 2008 from two geomagnetic observatories, one located in the proximity of the Vrancea seismic zone and another one situated 120 km away. For each geomagnetic anomaly identified, the daily seismic energy released was plotted logarithmically, along with seismicity and Kp indices. Additionally, the daily seismic energy released was also plotted logarithmically for all earthquakes with Mw ≥3. To identify variations in the By component, datasets recorded at Muntele Rosu (MLR) were compared with those recorded at Surlari National Geomagnetic Observatory (SUA), to discriminate between global magnetic variations associated with solar activity and possible seismo–electromagnetic variations. The standard deviation (SDBy) was calculated for each anomaly recorded on the By component of the magnetic field and compared with the cumulative seismic energy release. To determine if this type of variation was present in other components of the magnetic field, the following ratios were calculated for all data recorded at Muntele Rosu: Bz/Bx, Bz/By, and Bz/BH. The size of the anomalies resulting from the standard deviation measured on the By component (SDBy) partially validates the relationship between the size of the anomalies and the seismic energy release during the anomaly. The relationship between the released seismic energy and the anomaly magnitude is vaguely respected, but these variations seem to follow two patterns. One pattern is described by smooth decreases, and the other pattern involves decreases where the By component varies significantly over short periods, generating decreases/increases in steps. It was noticed that seismic activity is greater for the second pattern. Additionally, using standard deviation measured on the magnetic field represents a great tool to discriminate external magnetic field variations from local, possibly seismo–magnetic variations.

Authors:
Țigănescu A., Grecu B., Mărmureanu A., Ioenscu C.

Abstract:

Authors:
Armeanu I., Chircea A., Ciobanu I., Craiu A., Craiu G.M., Dinescu R., Mihai M., Predoiu A., Tolea A., Vărzaru L.C., Borleanu F., Neagoe C., Radulian M., Popa M.

Abstract:
An intense seismic sequence occurred in 2023 in Gorj area (Romania), part of the Central Southern Carpathians seismic zone, having a doublet as main shocks. The first one, with a local magnitude of 5.2, was recorded on February 13 at 14:58:09 UTC, and the second one, with a local magnitude of 5.7, was recorded the next day at 13:16:52 UTC. The data was processed using recordings from the Romania Seismic Network stations. This database contains the parameters of the two main shocks and over 2000 aftershocks as recorded and located up to the present. It will be continuously updated.

Authors:
Craiu M., Craiu A., Mihai M., Mărmureanu A.

Abstract:
Parameters of the focal mechanism catalog for Vrancea (Romania) intermediate-depth earthquakes (2005-2020). Here we report the following: date (year/month/day), time (hh:mm:ss), lat (latitude north in degrees) and long (longitude east in degrees), depth (km), Mw (magnitude), Strike1, Dip1 and Rake1 (strike, dip, rake of the first fault plane in degrees), Strike2, Dip2 and Rake2 (strike, dip, rake of the second fault plane in degrees), P-a, P-p, T-a, T-p ( P and T axis, azimuth and plunge angle in degrees), SHmax, Shmin (azimuth), R’ (stress regime index), SR( Stress regime), Nr P (number of polarities), Err P (errors of polarities).

Authors:
Manea E., Hill M., Kaiser A., Wotherspoon L., Bourguignon S., Bora S., Stolte A.

Abstract:

Authors:
Radulian M., Bala A., Poiată N., Tătaru D., Popa M., Dinescu R.

Abstract:
A significant growth in seismicity was recorded in 2023 in the Southern Carpa-thians and northern Banat region in Romania. The two earthquake sequences oc-curred close to Tg. Jiu (Gorj area) and Arad cities are the strongest episodes of seismicity ever recorded in these areas. The relocation of the hypocenters using Joint Hypocenter Method outlines alignments in agreement with the fault plane solutions. The twin shocks of magnitude above 5 recorded in the Gorj area were triggered at the bottom side of the aftershocks area and the rupture propagated unilaterally roughly east to west. The focal mechanisms comply with the exten-sional stress regime in the region. The development of aftershocks over an unu-sual long-time interval (more than 3000 aftershocks since 13 February 2023 up to the present in the Gorj area) could be explained by particular mechanisms, such as delayed dynamic triggering or gravitational triggering which are specific for crustal extensional environments. The intensifications in seismicity took place in areas previously considered with low-to-moderate seismic hazard, neglected by the definition of the seismogenic zones adopted up to now in seismic hazard computation. By no means, reconsidering the recent earthquake sources in the western area of the Southern Carpathians and their link with the local active faults are necessary for a realistic assessment of the seismic hazard in the south-western part of Romania.

Authors:
Radulian M., Popa M., Dinescu R., Bala A.

Abstract:
A significant seismic sequence started on 13 Feb. 2023 at 14:58 GMT with a mainshock of 5.2 ML located at 17 km depth and at 14 km distance NW from Targu Jiu city. The first shock was followed by 16 aftershocks with magnitudes between 2.1 and 3.4 after which a second mainshock of magnitude 5.7 was triggered next day, 14 Feb., at 13:16 GMT. The largest acceleration at the second shock (105.25 cm/s2) was recorded at Gura Zlata station as well. The seismic events hypocenters are established by several methods. First two main shocks (with ML>5) are preliminary located using 10 seismic stations around the seismic zone. The second set of locations have as input data from seismic stations situated 100 km distance around the active area. The third set of locations are realized with all available Romanian seismic stations placed all over the country. The third locations of the main shocks performed routinely by the National Institute for Earth Physics (NIEP), Romania, placed the two main shocks several kilometers to the south and out from the cloud of aftershocks. As shown in our analysis, this is an artifact when different sets of stations are used in location procedure that can be explained based on the difference between the lithosphere models in different parts of Romania and the simplified model used by NIEP for routinely determination of events location with Antelope program.

Authors:
Craiu M., Craiu A., Mărmureanu A., Diaconescu M., Mihai M.

Abstract:
NIEP is Tsunami National Contact (TNC) and Tsunami Warning Focal Points (TWFP) of Romania for the Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (ICG/NEAMTWS) and attended different tsunami exercises (NEAMWave14, NEAMWave17, NEAMWave21)

Authors:
Manea E., Kaiser A., Hill M., Wotherspoon L., Bourguignon B., Bora S., Stolte A.

Abstract:
Starting with 2007, NIEP developed the tsunami research field, by different national, regional and international projects, with a total number of seven past projects: PROFET - Multidisciplinary researches on natural hazards. Case study: tsunami type phenomenon in the Black Sea (national project); MARINEGEOHAZARD - Set-up and implementation of key core components of a regional early-warning system for marine geo-hazards of risk to the Romanian-Bulgarian Black Sea coastal area (regional project); GTIMS - Global Tsunami Informal Monitoring Service (international project); GTIMS2 - Global Tsunami Informal Monitoring Service 2 (international project); ASTARTE - Assessment, STrategy And Risk Reduction for Tsunamis in Europe - Black Sea (international project); ARISTOTLE - All Risk Integrated System Towards the Holistic Early-Warning (international project) and AGITHAR - Accelerating Global Science in Tsunami Hazard and Risk Analysis (international project). In the framework of ASTARTE project, questionnaires were performed along the Romanian shoreline, the results (Constantin et al.,2017) showing that people are not properly informed regarding tsunami risk and/or how to behave, thus the necessity of education and dissemination.

Authors:
Kalmár, D., Petrescu, L., Stipčević, J., Balázs, A., János Kovács, I., & the AlpArray and PACASE Working Groups

Abstract:
The lithosphere-asthenosphere boundary and mid-lithospheric discontinuities are primary attributes of the upper mantle. The Pannonian region is an extensional sedimentary basin enclosed by collisional orogens. Here, we estimate the negative phase depth of S-to-P receiver functions to image the lithospheric thickness and other discontinuities with high resolution, based on the recent dense seismological broadband networks. The lithosphere-asthenosphere boundary is relatively shallow (<90 km) in the Pannonian Basin system, and deeper (∼90–140 km) in the surrounding orogens, where average surface heat flow values are higher (120 mW/m2) and lower (50–70 mW/m2), respectively. The 1D and 2D common conversion point migration with 3D velocity model provide comparable but different resolution images beneath the wider region of the Pannonian Basin. We obtained deeper values in the Western (∼120 km) and Southern-Carpathians orogens (∼135 km). Furthermore, we provide new information on the lithospheric thickness and its seismic properties in the eastern part of the study region (e.g., Apuseni Mountains (∼95 km), Eastern-Carpathians (∼120 km), Moesian Platform (∼90 km) and Transylvanian Basin (∼85 km). The shallower negative phase depth can be interpreted as the lithosphere-asthenosphere boundary beneath the Pannonian Basin system in agreement with its high heat flow values. In contrast, the deeper negative phase depth estimates in the colder surroundings can be interpreted as intra- or mid-lithospheric discontinuities, when compared with local seismic tomography models. In this region, the correlation with heat flow implies that the observed negative phase depth is of thermo-chemical or rheological nature.

Authors:
Oros E., Popa M., Paulescu D., Plăcintă A.O., Ghiță C.

Abstract:
We present a refined and the most complete catalogue of the focal mechanisms for the Intra-Carpathian region of Romania. It contains the high-quality solutions computed for 1217 earthquakes recorded between 1909 and 2018. Primary data gathered from the original seismograms and seismic bulletins have been used to compute the source parameters and focal mechanisms solutions. The focal mechanisms have been obtained using the HASH method by the polarities and S/P amplitudes ratios inversion. Our catalogue provides data necessary for the investigation of the contemporary stress field at different scales with high spatial and temporal resolution. We determined the stress field characteristics through formal inversion of focal mechanisms and also computed the reactivation potential of the active fault systems using the Win-Tensor program. The stress field is heterogeneous, with SHmax significantly deviating from the first-order stress field direction and also with strong local variations in the stress regime.

Authors:
Oros E., Popa M., Paulescu D., Plăcintă A.O., Ghiţă C.

Abstract:
We present a refined and the most complete catalogue of the focal mechanisms for the Intra-Carpathian region of Romania. It contains the high-quality solutions computed for 1217 earthquakes recorded between 1909 and 2018. Primary data gathered from the original seismograms and seismic bulletins have been used to compute the source parameters and focal mechanisms solutions. The focal mechanisms have been obtained using the HASH method by the polarities and S/P amplitudes ratios inversion. Our catalogue provides data necessary for the investigation of the contemporary stress field at different scales with high spatial and temporal resolution. We determined the stress field characteristics through formal inversion of focal mechanisms and also computed the reactivation potential of the active fault systems using the Win‑Tensor program. The stress field is heterogeneous, with SHmax significantly deviating from the first-order stress field direction and also with strong local variations in the stress regime.

Authors:
Mihai M., Radulian M., Popa M., Grecu B.

Abstract:
ANTELOPE revised locations, extracted from the INCDFP catalogue, were used as input data for relocation with JHD method. The basic idea behind this technique is to simultaneously determine an optimum 1-D structural model for the target area, to relocate the events and to fix a common set of station corrections. Under appropriate conditions, the station corrections reproduce the unmodelled velocity variations, and thus can significantly improve the location of events. These corrections are related to local effects characterizing the station site. The relocated earthquakes and quarry blasts using JHD better delimit specific clusters in comparison with routine catalog locations.

Authors:
Apostol B.F., Cune L.C.

Abstract:
The time dependence of the parameter of the Gutenberg-Richter (GR) magnitude distribution is computed for foreshock sequences of earthquakes, correlated with the main shock, by using the geometric-growth model of earthquake focus, the magnitude distribution of correlated earthquakes and the time-magnitude correlations, derived recently. It is shown that this parameter decreases in time in the foreshock sequence, from the background values down to the main shock. If correlations are present, this time dependence and the time-magnitude correlations provide a tool of monitoring the foreshock seismic activity. We discuss the relevance of such an analysis for the occurrence moment and the magnitude of a main shock. The discussion is applied to a few Vrancea main shocks and the precursory seismic activity of the l'Aquila earthquake. The limitations of such an analysis are discussed.

Authors:
Apostol B.F.

Abstract:
The elastic wave equation with seismic tensorial force is solved in a homogeneous and isotropic medium (the Earth). Spherical-shell waves are obtained, which are associated to the primary P and S seismic waves. It is shown that these waves produce secondary waves with sources on the plane surface of a half-space, which have the form of abrupt walls with a long tail, propagating in the interior and on the surface of the half-space. These secondary waves are associated to the seismic mainshock. The results, previously reported, are re-derived using Fourier transformations and specific regularization procedures. The relevance of this seismic motion for the ground motion, the seismographs’ recordings and the effect of the inhomogeneities in the medium are discussed.

Authors:
Moldovan I.A., Oros E., Vanciu Rău A., Constantin A.P., Diaconescu M., Manea M.L., Lungu M.

Abstract:

Authors:
Bălan S.F., Apostol B.F., Dăneț A.

Abstract:
There is a need for safer constructed medium in order to respond to the constant necessity for raising the security level of human society to earthquakes impact. In this respect the buildings monitoring in areas subjected to seismic site effects provides the possibility of getting immediate and reliable information on the status of certain structures, which enables decision makers to better allocate resources and to direct rescue operations. A procedure is implemented, which allows to perform real-time data acquisition, data exchange and data analysis from structures exposed to seismic excitation or under ambient vibration. The processed recordings are used to deliver information in real time about the seismic event. Engineering seismology parameters are computed: maximum acceleration, spectral acceleration, corresponding oscillation periods, etc., on both structures and free field. The output is conceived as a standard report on the characteristic response of the instrumented building. In the paper such an approach is described in an extended and thoroughly version, for two instrumented buildings, located in different areas, under the last year’s strongest seismic event of 2022.11.03, Mw = 5 that hit the Romanian territory.

Authors:
Apostol, B. F., Balan, S. F., Danet, A.

Abstract:
The seismic recordings from certain types of buildings in urban areas during moderate earthquakes from Vrancea-intermediate depth focal region are processed and analysed. One of the most important element in hazard evaluation at national level is the seismic recording network which has been upgraded in the last years up to over 20 strong motion accelerometers in Bucharest and 135 in Romania with easy data handling (accelerations easy to transform in displacements). The general behaviour of reinforced concrete buildings in Bucharest Metropolis during destructive seismic events from Vrancea-intermediate depth focal region is briefly described. The analysis of the elastic response spectra is made for four buildings subjected to the two recent earthquakes with magnitude higher than 4.8, of October 28, 2018 and January 31, 2020 from Vranceaintermediate depth seismic zone. The information consisting in maximum level of the pseudo-acceleration to which the buildings were subjected may be used to detect and quantify any exceedance of the code spectra of interest in near real-time. The recorded earthquakes data are transmitted in real time to the National Data Centre. The goal is to develop and implement modern techniques and tools able to estimate the effect of earthquakes on the built environment in the shortest time possible after a major earthquake

Authors:
Petrescu L., Borleanu F., Kästle E., Stephenson R., Plăcintă A.O., Liashchuk O.I.

Abstract:
The Eastern European lithosphere is a natural laboratory to study continental formation and evolution through time, comprising Archean continental remnants, Proterozoic rifts and belts, and younger accreted terranes. We investigate the seismic structure of the East European Craton (EEC) crust and uppermost mantle, and the transition from Precambrian to Phanerozoic Europe across the Trans European Suture Zone (TESZ) using probabilistic transdimensional ambient noise tomography. We cross-correlate noise recorded at broadband seismic stations from Eastern, Northern, and Central Europe, remove earthquake signals using continuous wavelet transform, and extract Rayleigh wave phase velocity dispersion curves. We invert these for the highest resolution shear wave velocity model of the Eastern European lithosphere to date, using Markov chain Monte Carlo Bayesian inversion. Our shear wave velocity model exhibits spatial correlation with major tectonic units and bears similarities with active seismic survey profiles in terms of seismic velocity patterns and main discontinuities. The crust thickens across the TESZ boundary and the mantle is seismically faster than beneath younger terranes, consistent with a less dense Precambrian lithosphere in the EEC. The crust and lithosphere beneath the Pannonian region is hyper-extended but the adjacent Transylvanian basin crust shows significant heterogeneity. The Precambrian building blocks of the EEC exhibit contrasting seismic fabrics. The Baltic orogens of Fennoscandia are underlain by uniform crust with a flat Moho, while Sarmatia shows alternating high and low velocity layers and a regional south-dipping crustal boundary from beneath the Ukrainian Shield towards the Crimean Peninsula. The last observation supports a geodynamic style driven by horizontal rather than vertical tectonics, with fundamental implications for the formation and evolution of early continents.

Authors:
Yagi Y., Okuwaki R., Enescu B., Lu J.

Abstract:
In September 2022, two destructive earthquakes of moment magnitude (Mw) 6.6 (foreshock) and 7.1 (mainshock) occurred in Taitung County, south-eastern Taiwan. To understand their complex rupture processes, we analysed these earthquakes using the Potency Density Tensor Inversion method, which can stably estimate the rupture propagation process, including fault geometry, without overfitting the data. The analyses revealed that the major rupture of the foreshock propagated towards shallow depth, in a south–southwest direction, following an initial rupture that propagated towards the deeper part of the fault. The mainshock, with its epicentre on the north–northeast side of that of the foreshock, consists of two distinct episodes. During the first episode (0–10 s), the initial rupture propagated north–northeast, through a deep path, followed by the main rupture that propagated bilaterally in a north–northeast and south–southwest direction. The second rupture episode (10–16 s) started near the hypocentre of the mainshock, and the rupture propagated towards the shallow side of the fault. The results suggest that the stress concentration from both the foreshock and mainshock’s first rupture episode may have caused the second rupture episode in the high fracture surface energy area between the foreshock and the first rupture episode of the mainshock. The irregular rupture process of the foreshock and mainshock may reflect the heterogeneity of stress and structure in the source region.

Authors:
Borleanu F., Petrescu L., Seghedi I., Thomas C., De Sienna L.

Abstract:
Sedimentary basins in collisional settings result from interactions within and between lithospheric plates and sublithospheric mantle. Imaging their structure brings fundamental constraints to both the extraction of hydrocarbon or geothermal resources and seismic hazard analyses, especially in seismogenic areas affected by fluid percolation. Seismic attenuation is highly sensitive to stress, fluid saturation, and fluid-rock interaction and can often constrain small changes in the Earth's matrix better than seismic velocity. Here, we separate different attenuation mechanisms (scattering and absorption) at multiple frequencies and map them in space to constrain the properties of the Carpathian Orogen and the surrounding basins. The separation is achieved by determining S-wave peak delay times and late-time coda quality factors based on first-order Tikhonov inversion and analytical sensitivity kernels. We analysed 366 small-to-moderate crustal local earthquakes (0.7 < ML < 5.8) recorded by permanent and temporary stations operated by the Romanian Seismic Network between 2008 and 2021. Scattering and absorption appear to be frequency-dependent and highly heterogeneous throughout the region. High scattering and absorption characterise the Vrancea Seismic Zone, located in the Eastern Carpathian bend region, at all frequencies, likely due to high-stress rate and fluid inclusions. The seismically-active bend of the collisional orogen also shows high absorption and high scattering, particularly at low frequencies (∼3 Hz). Low scattering and high absorption features are observed across the Danubian section of the South Carpathians, marking the contact with the Pannonian Basin, which sits on top of a thin and highly-extended lithosphere. A transition from high to low-scattering regimes with increasing frequencies could mark small-scale heterogeneous structures in the Transylvanian Basin, an elevated sedimentary unit surrounded by high topography, comprising Cretaceous Neogene sediments deposited on top of oceanic ophiolites.

Authors:
Constantin A.P., Manea L.M., Diaconescu M., Moldovan I.A.

Abstract:
Vrancea is the major region with the highest seismic hazard in Romania. We investigate macroseismic data and analyze also the influence of local geological structure on earthquake intensities in many areas affected by these earthquakes. It's known that the soft sediments existing in many areas of the territory have also a strong influence on seismic ground motion. The topographic effects can be also responsible for this apparent amplification of the ground motion. In this paper we determined intensities according to MSK Macroseismic Scale for seven small to moderate earthquakes (Mw > 4.5) occurred between 2013 and 2020 in Vrancea seismogenic region. Following the shaking, many people submitted reports to NIEP via the online questionnaire in which recorded their experience, while others reported macroseismic observations in the classic questionnaires requested by NIEP experts to the local authorities. The intensity data points resulted after analysis of the collected macroseismic data showed that a maximum int nsity of V–VI was experienced for many localities for four of the seven earthquakes, also isolated/sporadic a few IDPs of degree VI were assigned. The shaking with intensity of V was experienced with a majority in the case of all the earthquakes studied here. Surprisingly, strong shaking of this intensity (V) was also experienced at great distances, about hundreds of km from the epicenter.

Authors:
Tolea A., Grecu B., Neagoe C., Moldovan I.A., Toader V.E.

Abstract:
In the absence of earthquakes, seismic stations continuously record the Earth's vibrations, called ambient seismic noise (ASN). The main concern regarding the ASN records is improving the seismic data quality using different tools developed especially for this purpose. Power Spectral Densities (PSD) and their corresponding Probability Density Functions (PDF) are tools used to evaluate the station performance and reveal the noise level at the station’s site. For high frequencies (>1 Hz), the noise sources are from cultural activities and show diurnal variation, while for low frequencies (<1 Hz), the noise is generated by natural sources and shows seasonal variation. In this study, we analyzed the vertical components of the Bucovina array seismic network (BURAR) to characterize the noise levels at the stations and investigate noise variations in space and time. We computed four-year spectrograms for some elements of the array that revealed an increase of ASN in the 2–5 Hz frequency range during the warmer seasos, contrary to the colder months. On the other hand, at lower frequencies (0.5–1 Hz), the power of seismic noise increases during the year’s colder months. We examined the relationship between noise levels and weather parameters (e.g., wind speed) for the station where the seismic sensor is collocated, with a weather station. We observed that an increase in wind speed leads to an increase in the noise level at high frequencies (> 2 Hz).

Authors:
Moldovan I.A., Popescu E., Radulian M., Enescu B., Plăcintă A.O., Ghiță C., Constantin A.P.

Abstract:
Seismicity clustering characterizes the seismic process. We compute the fractal dimension for the Vrancea earthquakes recorded between 1995 and 2008, both in the crust and in the mantle. The fractal dimension shows a visible decreasing anomaly preceding the largest Mw = 6.0 earthquake in the dataset occurred on 27th of October 2004.

Authors:
Petrescu L., Plăcintă A.O., Borleanu F., Radulian M., Cioflan. C.

Abstract:
The Vrancea seismic zone (VSZ), located in Romania, at the sharp bend of the southeast Carpathians, is an anomalous intraplate seismic nest releasing the largest strain in continental Europe. The last powerful earthquake in Vrancea occurred in 1977 causing significant damage to the densely populated cities in southeast Romania. The seismic infrastructure was underdeveloped at that time and the earthquake was not well recorded locally. Using ambient seismic noise recorded at modern broadband seismic stations around Vrancea in the year 2020, and the approximate moment tensor solutions of significant earthquakes Mw>6 since 1977, we reconstruct ground‐motion waveforms recorded by modern seismometers decades after their occurrence. The virtual earthquake approach uses empirical Green’s functions from ambient noise cross correlations between pairs of seismic stations and adds the signatures of a model earthquake: double couple mechanism, buried source, and a realistic earth model in the epicentral area. Ambient noise data capture the signatures of complex subsurface structures and the 3D path effects, providing a more physically accurate representation of the seismic wavefield than purely synthetic data. Our new results demonstrate the viability of this innovative method and provide a unique opportunity for more accurate seismic hazard analysis in intraplate seismic zones with insufficient instrumental data.

Authors:
Popescu T., Tătaru D., Țigănescu A., Toma-Dănilă D., Năstase E.

Abstract:

Authors:
Hill M.P., Kaiser A.E., Wotherspoon L.M., Manea E.F.

Abstract:
The 30-m time-averaged shear-wave velocity (Vs30) and the fundamental site period (T0) are useful parameters for understanding site conditions, informing geotechnical and seismic hazard studies as well as infrastructure planning. Unfortunately, sites where these data are measured can be sparse or poorly distributed posing challenges in mapping these properties over an entire city. To help resolve the spatial problem, this study has used a detailed 3D geological model and assigned shear wave velocity values for the modelled subsurface material units to create maps of estimated Vs30 and T0 for the Wellington City CBD. We compare the model estimated values with measured site parameters from surface or down-hole geophysical data and explore the variability of the model results using Monte Carlo Simulations.

Authors:
A.C. Stolte, C. Brown, K.L. Lee, L.M. Wotherspoon, E.F. Manea

Abstract:
The effects of soil stratigraphy and sedimentary basins on earthquake ground shaking are well-established. These effects can be represented using a range of site metrics, with the focus of this paper being the fundamental period of vibration of soil above bedrock (T0). T0 has been used to differentiate between subsoil site class C and D in NZS1170.5 and in the seismic microzonation of sedimentary basins as a proxy for basin depth. An increasingly common method to estimate site period is via identification of peaks in the Horizonal-to-Vertical Spectral Ratio of microtremor (mHVSR) data. Several recent studies in Aotearoa New Zealand and internationally have focused on the temporary deployment of sensors to characterise sedimentary basins on local and regional scales. This paper leverages a dataset of ambient vibration recordings from several studies collected using instrumentation borrowed from the Incorporated Research Institutions for Seismology (IRIS). Broadband seismometers have been deployed at 785 locations across the country. Data was publicly available at 311 sites and suitable for mHVSR analysis at 113 sites. New estimates for site period are presented herein for sites across the country, including Southland, Otago, along the Alpine Fault, and throughout the Taupō Volcanic Zone. All provide insight into sedimentary basin and earthquake ground shaking.

Authors:
Zaharia B., Grecu B., Tolea A., Radulian M.

Abstract:
Technological advancements and the appearance of low-cost Raspberry Shake seismographs have enabled the development of citizen science seismic networks in many areas worldwide. These networks can help reduce seismic risk and increase citizens’ understanding of seismology and earthquakes. Such a network exists in Bucharest, one of the cities in Europe that are struck and affected by strong Vrancea earthquakes. The paper aims to show that data from such networks can be used in both outreach programs and research studies. There are presented, for the first time, seismic observations collected over two years beginning in the summer of 2020 in the Bucharest area based on the low-cost seismometers from the citizen science Raspberry Shake network. A significant number of earthquakes from the Vrancea region were recorded by the Bucharest Raspberry Shake Seismic Network (BRSSN). Some of them were felt by Bucharest inhabitants. The National Institute for Earth Physics in Magurele (Romania) organizes educational events that promote geosciences among the population and presents the tools at its disposal for a better understanding of earthquakes and their effects, contributing this way to the development of the concept of citizen science. Citizens are the first witnesses to seismic events and the citizen science seismic network provides them with the first direct information about the event via web apps available for any internet-connected device. Their involvement as non-professional participants helps in providing data for scientists via questionnaire forms to improve scientific research for earthquake assessment. Since citizen seismometers are installed in urban areas, an analysis of the ambient seismic noise (ASN) was performed in addition to the analysis of recorded seismic events. The analysis indicates that the level of seismic noise is mainly controlled by human activities. At the same time, for one citizen seismometer installed in a school in Bucharest, the results show patterns of noise variations due to students’ activity.

Authors:
Armeanu I., Borleanu F., Vărzaru L., Ghica D., Popa M.

Abstract:
Over the previous decades, seismic activity has sporadically increased along the western edge of the European Platform. Although the Romanian Seismic Network has been continuously enlarged, the growth in the number of events in the Romanian earthquake catalogue, ROMPLUS, in this area does not always follow the number of newly installed stations. To shed light on the patterns of seismic activity in this region, we performed a statistical analysis of events recorded between 2005 and 2021 in the ROMPLUS catalogue and used waveform correlation analysis to investigate the similarity degree and nature of these events. The poorly located events were relocated after the seismic phases were manually examined. We show that a large number of events are clustered around fault systems distributed near several quarries.

Authors:
Bala A., Toma-Dănilă D., Ciugudean-Toma V.

Abstract:
Especially after the March 4, 1977 disastrous Vrancea earthquake (Mw 7.4), the necessity for a detailed local seismic hazard map for Bucharest, the capital city of Romania, was recognized. The distribution of earthquake effects as well as subsequent earthquake recordings throughout the city revealed a high variability of seismic ground motion, not only due to source effects but also due to local site effects. The geophysical methods employed in recent years allowed only limited results, so that there are no general geological models of the city applicable to a city-wide analysis. By using a recently compiled geological database, which relies mostly on several hundreds of borehole measurements performed for the subway in Bucharest and a recent DEM for the area, this study establishes the positions of the main seven Quaternary layers beneath the city. A 3D geological model is obtained by interpolation using the GIS kriging method. The 3D geologic model covers most of the city area, reflecting the confidence boundaries. This study also discusses geotechnical data availability and the influence of hydrogeology on the analysis of microzonation of the Bucharest city area.

Authors:
Craiu M., Craiu A., Mihai M., Mărmureanu A.

Abstract:
The seismicity of Romania is mostly represented by earthquakes produced by the Vrancea seismic source with intermediate depth events (3 shocks/century with magnitude MW greater than 7.0). The seismic activity in Romania also includes crustal earthquakes. The crustal seismicity is more scattered and moderate compared to the intermediate-depth one. A stable and automatic method has been implemented in the real-time data acquisition and processing system ANTELOPE to estimate the seismic moment, the moment magnitude and the corner frequency of events recorded by the velocity sensors, using spectral analysis applied to S waves. The main goals are the independent estimation of the seismic moment and the common characterization for all events recorded by the National Seismic Network. The main target of this paper is represented by the fast estimation of moment magnitude MW and ground motion parameters that are derived using Gallo et al. (Bull Earthquake Eng 12:185–202, 2014) methodology and their validation with other magnitude determination algorithms existing at the National Institute for Earth Physics (NIEP). To test this new methodology, we have analyzed 331 seismic events, most of them being automaticaly located, and afterwards added a new, manually processed solution for events with ML ≥ 4.5, to obtain a larger interval of magnitudes. © 2023, Akadémiai Kiadó.

Authors:
Constantin A.P., Diaconescu M.

Abstract:

Authors:
Galiana-Merino J.J., Molina S., Kharazian A., Toader V.E., Moldovan I.A., Gómez I.

Abstract:
Many previous research studies have shown how local and even regional earthquakes can significantly affect the release of radon in the soil. The aim of this work is to investigate the relationship between radon measurements and the daily seismic activity rate and develop a methodology that allows estimating the seismic activity rate using only radon measurements. To carry out this study, the earthquake catalogue of the Vrancea region (Romania) has been used to estimate the daily seismic activity rate during a given time period, in which radon measurements were also recorded, from January 2016 to September 2020. The Vrancea zone represents the most active seismic zone in Europe and is located on the eastern edge of the strongly bent Carpathian arc. In the case of the radon measurements, seasonal behaviours and linear trends due to non-seismic factors have been identified and subsequently removed. The discrete wavelet transform has been used to analyse the radon signal at two different scales: long and short periods. From the analysis carried out on a long-period scale, an approximate linear relationship has been obtained between the radon series and the daily seismic activity rate, which provides insights into the behaviour of the seismic activity in the study region with only the radon information. In addition, the study reveals certain characteristics that could be used as precursors of earthquakes at different scales: weeks in the case of the estimated daily seismic activity rate, and days in the case of the short-period signal obtained by the wavelet analysis. The results obtained for this region allow us to hope that the analysis of the radon time series can become an effective complement to the conventional seismic analysis used in operational earthquake forecasting.

Authors:
Manea E.F., Cioflan C.O., Danciu L.

Abstract:
A newly compiled high-quality ground-shaking dataset of 207 intermediate-depth earthquakes recorded in the Vrancea region of the south-eastern Carpathian mountains in Romania was used to develop region-specific empirical predictive equations for various intensity measures: peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral acceleration up to 10 s. Besides common predictor variables (e.g. moment magnitude, depth, hypocentral distance, and site conditions), additional distance scaling parameters were added to describe the specific attenuation pattern observed at the stations located not only on the back and fore but also along the Carpathian arc. In this model, we introduce a proxy measure for the site as the fundamental frequency of resonance to characterize the site response at each recording seismic station beside the soil classes. To additionally reduce the site-to-site variability, a non-ergodic methodology was considered, resulting in a lower standard deviation of about 25%. Statistical evaluation of the newly proposed ground-motion models indicates robust performance compared to regional observations. The model shows significant improvements in describing the spatial variability (at different spectral ordinates), particularly for the fore-arc area of the Carpathians where a deep sedimentary basin is located. Furthermore, the model presented herein improves estimates of ground shaking at longer spectral ordinates (>1 s) in agreement with the observations. The proposed ground-motion models are valid for hypocentral distances less than 500 km, depths over 70 km and within the moment magnitude range of 4.0–7.4.

Authors:
Apostol B.F., Borleanu F., Cune L.C.

Abstract:
A direct, practical and operative procedure is described for deriving the parameters of the seismic source and earthquakes from the ground displacement of the P and S waves recorded at a local site on Earth’s surface. The procedure gives the seismic-moment tensor, the earthquake energy and magnitude, the orientation of the fault and the direction of the tectonic slip, the duration of the focal seismic activity and the dimension of the focal region (fault). The (previously published) theory underlying this procedure is briefly discussed. The aim of this paper is to provide a detailed description of how this theory can be used for practical purposes. Two specific examples of Vrancea earthquakes (October 10, 2018 and September 23, 2016) are presented.

Authors:
Moldovan I.A., Apostol A., Muntean A., Ghiță C., Toader V.E., Ambrosius B.

Abstract:
In the last 300 years the window of time for two consecutive large and destructive intermediate-depth earthquakes in Vrancea (Romania) was between 36 and 102 years. An explanation for the larger window of time might be a release of stress produced by a slow-slip-event (SSE). In a vertical sinking slab slightly attached from the Earth’s crust both large earthquakes and SSE are expected to generate a downward movement in the vertical displacements of GPS data. The building-up of stress in the asperity preventing a steady aseismic sinking was expected to be transmitted upwards to faults in the crust and recorded based on a magnetotelluric phase splitting effect. A large stress build-up has been suggested around a fault in the years 2012–2013, but no large earthquake was recorded. We supposed a large SSE in the year 2013–2014 with a duration of 13 months released the accumulated stress. GPS stations in the epicentral region of Vrancea seismic active region supported our suggestion by showing a downward displacement of vertical data obtained for the year 2014. However, the vertical displacements are small and other possible causes than SSE need to be taken into account.

Authors:
Năstase E., Muntean A., Nistor S., Dimitriu S., Jecu M.N., Suba N.S.

Abstract:
We describe a comprehensive analysis of permanent Romanian Global Navigation Satellite System (GNSS) sites’ on vertical position time series from data spanning 3–20 years. The GPS observations were computed using Gipsy X software, we apply Global Positioning System (GPS) Imaging, a new technique for robust estimation of the vertical velocity field of the Earth’s surface, and the final estimates to obtain the stations’ vertical deformations velocities were analyzed using Maximum Likelihood Estimation (MLE) and Median Interannual Difference Adjusted for Skewness (MIDAS) trend estimator which is insensitive to undocumented steps, outliers, seasonality, and heteroscedasticity. We focus on the known national GPS observation level model in the Carpathian-Danubian-Pontic area to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates at 45 degrees latitudes. Finally, we interpolate the data using weighted median estimation on a grid. The resulting velocity field is temporally and spatially robust, and edges in the field remain sharp. Our investigation results into a case study and an integrated thematic service of influences that could be applied to the revised analysis strategies of vertical deformations over the Romanian region.

Authors:
Țigănescu A., Craifaleanu I.G., Aldea A., Grecu B., Văcăreanu R., Toma-Dănilă D., Bălan S.F., Dragomir C.S.

Abstract:
The seismic instrumentation of structures in order to assess their condition and to track it over long periods or after representative events has proven to be a topic of large interest, under continuous development at international level. The seismic hazard of Romania poses one of the most dangerous threats for the country, in terms of potential physical and socio-economic losses. In recent years, taking advantage of the new scientific and technological advances, among which the exponential growth in computational resources, significant improvements have been made in extending the seismic networks for structural monitoring and using the data as input for products and services addressed not only to the research community but also to stakeholders. The paper covers focused aspects of the topic for Romania, referring to past developments of the most important institutions and seismic networks in the country and the current status, including the research and regulatory gaps. Currently, three main research and academic institutions perform structural health monitoring of twenty-two buildings in Romania. As the number of monitored buildings grows and new actors in the private sector start to get involved in the process, the need for data standardization and a regulatory framework increases. Ongoing national and international projects (PREVENT, SETTING, TURNkey) address these issues and outline the roadmap for future actions of the main institutions responsible for seismic risk reduction, including authorities, research and academia.

Authors:
Tătaru D., Năstase E., Toma-Dănilă D., Grecu B., Țigănescu A.

Abstract:
The global development of society requires constant updating of the objectives that education pursues and how they are achieved. Science education is an area undergoing advanced transformation, both at the level of objectives and methodologies, with a strong social, economic, and knowledge impact. Research-based education is a well-established term, especially in the higher education system. More studies and key policy documents argue that education must be based on cutting-edge research. Essential in this equation is the existence of dedicated frameworks (tools, events, courses, and strategies) and knowledgeable mentors and developers. Through reliable tools, we refer to real learning contexts created by the parties involved in studies and research together with those who analyze how students receive information at their level of knowledge and understanding. Such a context is also the integration platforms facilitating access to data, products, and research services. There are many such platforms, but not so many of them develop components dedicated to an important user category: pupils, students and their teachers. Considering this category of beneficiaries also means collecting feedback on what is relevant to them, what the platform exposes as information, and what actions they can take to be immersed in the research process. Future 'Environmental Data Scientists' will need to draw on multiple data and information sources, using data analysis, statistics, and models to create knowledge that is communicated effectively to decision-makers in government, industry, and civil society. Platforms that “expose” monitoring data, offer access to research products, and allow both the interoperability and reproducibility of science and the transparency of the process leading to a shared outcome are essential for the much-claimed paradigm shift towards open science.

Authors:
Victorin Toader , Constantin Ionescu , IREN MOLDOVAN , Lucian Palangeanu

Abstract:
The Catalogue is a compilation containing 1299 events (Mw≥3.0) that occurred between 08.01.1223 and 31.12.1989 within the Intra-Carpathians Region of Romania. The focal parameters of imported earthquakes have been revised using all primary data collected from the available sources (macroseismic observations, documents, books, private notes, newspapers, etc.). Historical instrumental data are from digitized analogue seismograms and bulletins collected through EuroSeismos and Sismos-Neries 2006-2010 projects. These data have been processed using modern criteria, methods and recalibrated relationships (eg EMS scales, digital techniques, macroseismic location, Mw estimation). The final catalogue contains several newly identified earthquakes. Also, several events from the Romplus catalogue were evaluated as false, being parameterized with a single macroseismic date (Io), in reality, these are intensity data points for strong earthquakes that occurred within neighbouring countries (see Oros 2011; Oros et al. 2021) The events were relocated by i) the MEEP macroseismic method (Musson&Jimenez, 2008) calibrated by Oros et al (2019) and ii) the grid-search technique using the Seisan program and the IASPEI91 velocity model when instrumental data have been available. The macroseismic locations were validated by comparison with those obtained by the BKW method (Bakun&Wentworth, 1997), recently calibrated by Oros et al (2019a). The macroseismic focal depth was estimated by Blake's relation using a new regional k coefficient computed by Oros et al (2019). When the macroseismic data were insufficient for applying the above-mentioned methods/relationships we used fixed values for the depth values calculated for the major morpho-structural large areas using recent digital data. The moment magnitude, Mw was calculated by i) MEEP/BKW methods or Mw=f (Io; Ri; Mi) conversions when the macroseismic intensity (Io), radii of isoseists (Ri) or instrumental magnitudes (Mi) were available and ii) the scalar moment method or a specific relationship (Oros et al, 2021) when historicl digitized seismograms we used. Mw estimated with MEEP/BKW methods were validated by comparison to those calculated with the relations Mw=f(Io/Imax; Ri; Ai) calibrated by Oros et al (2017).

Authors:
Victorin Toader , Constantin Ionescu , IREN MOLDOVAN , Lucian Palangeanu

Abstract:
'geobs' is a database about geophysical observation (radon, air ionization, CO2 and CO, Black Sea level, magnetic field, meteorological information, infrasound, ULF - VLF radio data, telluric currents, atmospheric static electricity etc.). These data are acquired in real time, displayed ('geobs panel example.jpg') and sent to the database at 5 minute intervals. From hour to hour, complete files are sent in which the sampling period varies from 1 s to 4 hours (in the case of radon). If limits are exceeded, warning messages are sent in real time. Monitoring stations and format of data are described in 'geobs st 5a.accdb' and 'geobs st 5a.inp' files (position, equipment type, data description). An example of data files are in the uploaded archives (format ASCII text with TAB delimiter). The data from data base can be accessed through an API (JSON and csv formats).

Authors:
Moldovan I.A., Toader V.E., Ionescu C.

Abstract:
The location (45.4909o latitude N, 25.945o longitude E) of Muntele Rosu geomagnetic observatory was picked by Dr. Dumitru Enescu (https://ro.wikipedia.org/wiki/Dumitru_Enescu ) in such a way as to ensure an optimum positioning with respect to Vrancea seismic area [1]. Moreover, this site was so chosen as to be distant from rail-roads and any other sources of noise in order to avoid disturbing signals. The geomagnetic observatory consists of: -one three-axis magnetic field sensor (fluxgate; ±70 μT measuring range), produced by “Bartington Instruments” MAG03 (UK) (1996-2019); -two three-axis magnetic field sensor (fluxgate; ±70 μT measuring range), produced by “Bartington Instruments” MAG03 (UK) (2019-2022); - a data logger-acquisition module (six channels, 24 bytes resolution, sample rate programmable), produced also by “Bartington Instruments”; - a router for data transmission; - a computer for data storage and preliminary processing.

Authors:
Zaharia B., Grecu B., Tătaru D.S., Neagoe C.

Abstract:
In the framework of the Romanian Educational Seismic Network project (ROEDUSEIS, 2012–2016), the National Institute for Earth Physics introduced in Romania the globally validated concept of using seismology as a tool for teaching geosciences by installing educational recording instruments in schools. The ROEDUSEIS network has been upgraded in the last year by installing new Raspberry Shake educational seismometers. This type of seismometer is very similar to the professional ones, in terms of performance, data acquisition and technical characteristics, the main difference being the low cost of the educational seismometers. In addition to the development of the ROEDUSEIS network, which allowed the recording of a larger number of earthquakes, several online tools have been implemented for the visualization and analysis of the recorded data. They are available for download and can be run online by teachers and students to improve their programming skills using real seismic data and learn more about Earth Sciences. These developments capitalize on and at the same time ensure the sustainability of the successful ROEDUSEIS projects results.

Authors:
Apostol B.F., Cioflan C.O., Mărmureanu A.

Abstract:
The seismic response recorded at two sites is analyzed, as it results from strong motion generated by Vrancea intermediate-depth seismic source. Three strongest seismic events generated by the Vrancea intermediate-depth seismic zone in the last five decades are chosen for this purpose. The evaluation is made for two areas of interest, as revealed by the spectral features influenced by the geological deposits under seismic excitation. The results are shown as response spectra at BucharestINCERC and Cernavoda downtown seismic stations for three strong earthquakes and other three weaker, collocated as pairs. The manner in which the seismic response for a broader range of magnitudes is affected by the specificity of each site is investigated. The shift of the predominant period is large at INCERC station, where high values are encountered, disposed of on a broader range. At this site, spectral ratios for each of the three pairs of seismic response spectra are performed, in order to showe the seismic source influence on local effects. The observed local amplification in correspondence to the site characteristics is highlighted.

Authors:
Bondar I., Sindelarova T., Ghica D., Mitterbauer U., Liashchuk A., Base J., Chum J., Czanik C., Ionescu C., Neagoe C., Pastzor M., Pichon A.L.

Abstract:
The Central and Eastern European Infrasound Network (CEEIN) has been established in 2018 with the collaboration of four research institutes, the Zentralanstalt für Meteorologie and Geodynamik (ZAMG), Vienna, Austria; the Institute of Atmospheric Physics of the Czech Academy of Sciences (CAS IAP), Prague, Czech Republic; the Research Centre for Astronomy and Earth Sciences of the Eötvös Loránd Research Network (ELKH CSFK), Budapest, Hungary; and the National Institute for Earth Physics (NIEP), Magurele, Romania. The Main Centre of Special Monitoring National Center for Control and Testing of Space Facilities, State Agency of Ukraine joined CEEIN in 2019. We show how the CEEIN infrasound arrays improve the detection capability of the European infrasound network and discuss coherent noise sources observed at CEEIN stations. We present the first CEEIN bulletin (2017-2020) of infrasound-only and seismo-acoustic events and using ground truth events, we demonstrate how adding infrasound observations to seismic data in the location algorithm improves location accuracy.

Authors:
Ghiță C., Tuta L., Moldovan I.A., Ionescu C., Nicolaescu M.

Abstract:
The parameters influencing the sea level measured with ultrasonic devices that are analyzed in this paper are the air temperature, atmospheric pressure and wind speed. As these variations are independent to each other and to the sea level, they can be removed from the measured sea level by applying a filtering algorithm based on independent component analysis (FastICA), adapted and improved for this application. The sound speed increases with temperature, so an internal temperature sensor is required to compensate for the sound-speed variation. Though this may improve the measurement accuracy, it is not enough to achieve the best results because there is a discrepancy between the internal sensor and the actual environment temperature. For high accuracy measurements, an external temperature sensor is required. In our case, we imported temperature datasets from a weather station, along with other datasets regarding atmospheric pressure and wind speed. The use of these external datasets, along with an algorithm based on principal component analysis (PCA) for error removal and the filtering algorithm based on FastICA for environmental phenomena extraction, allows us to achieve more accurate values for the Black Sea level in Constanta (2017–2020), independent of external influences.

Authors:
Plăcintă A.O., Borleanu F., Moldovan I.A., Coman A.

Abstract:
Seismic velocity is the geophysical property that has a key role in characterizing dynamic processes and the state of the stress around the faults, providing valuable information regarding the change in the tectonic regime. The stress in the crust is an important indicator of the possible occurrence of a major earthquake, and the variation of seismic velocities, in time, can provide a clearer picture on the tectonic processes taking place in the region. In the crust, velocities change before, during, and after earthquakes through several mechanisms related to fault deformations, pore pressure, stress changes, and recovery processes. In this study, we investigate the possible correlation between the changes of seismic velocities (Vp/Vs) in time and the occurrence of moderate size crustal and intermediate depth earthquakes from the Vrancea region. Our findings show that there are no significant variations in Vp/Vs for the intermediate depth earthquakes, while crustal events have decreased seismic activity prior to the main earthquake and no high Vp/Vs anomalies. Our results indicate key aspects, and such analyses should be carried out in real-time to continuously explore any unusual pattern pointed out by the seismic velocity changes. Vp/Vs and their standard errors can also be used to describe seismic activity patterns that shape the tectonic evolution of the area.

Authors:
Czirok L.,Kuslits L., Bozsó I., Radulian M., Gribovszki K.

Abstract:
The goal of this paper is to describe cluster analyses of the focal mechanism solutions estimated from local and teleseismic measurements and stress inversions to support the recent and previously published studies in the investigated region, that is the Vrancea seismic zone. We have applied different established clustering methods—e.g. hierarchical density-based clustering for applications with noise (HDBSCAN) and agglomerative hierarchical analysis—to the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the gathered seismic events. We have attempted to develop a fully automated algorithm for the classification of earthquakes and to support the further investigation of stress inversions. This algorithm does not call for the setting of hyper-parameters by the users, thus the contribution from any bias of the user can be reduced significantly and the time required to carry out the clustering can also be decreased. In most cases, the resulting stress tensors are in close agreement with those we found in the literature.

Authors:
Petrescu L., Moldovan I.A.

Abstract:
We designed a convolutional neural network application to detect seismic precursors in geomagnetic field records. Earthquakes are among the most destructive natural hazards on Earth, yet their short-term forecasting has not been achieved. Stress loading in dry rocks can generate electric currents that cause short-term changes to the geomagnetic field, yielding theoretically detectable pre-earthquake electromagnetic emissions. We propose a CNN model that scans windows of geomagnetic data streams and self-updates using nearby earthquakes as labels, under strict detectability criteria. We show how this model can be applied in three key seismotectonic settings, where geomagnetic observatories are optimally located in high-seismicity-rate epicentral areas. CNNs require large datasets to be able to accurately label seismic precursors, so we expect the model to improve as more data become available with time. At present, there is no synthetic data generator for this kind of application, so artificial data augmentation is not yet possible. However, this deep learning model serves to illustrate its potential usage in earthquake forecasting in a systematic and unbiased way. Our method can be prospectively applied to any kind of three-component dataset that may be physically connected to seismogenic processes at a given depth.

Authors:
Ardeleanu L., Neagoe C., Plăcintă A.O., Coman A.

Abstract:
1-D models for the quality factor along a few profiles crossing the Vrancea region and the adjacent extra-Carpathian zone have been recently developed, to reconstruct the ground motion generated by weak-to-moderate crustal earthquakes of Vrancea. The retrieved Q-structures reveal a consistent pattern of high attenuation at the bend of the Southeastern Carpathians. We discuss this result in relation with the outcomes of several studies that analyze wave attenuation along travel paths crossing both crustal and upper mantle structures of the study region, to emphasize the contribution of the shallow structure to the observed attenuation pattern.

Authors:
Mihai A., Roban R.D., Toader V.E., Lingvay I., Ciogescu O.

Abstract:
In absence of core samples and open-hole well-log data, the broken bits of rock removed from the borehole during the drilling process represent in many cases the only lithological data that is recovered from a well. The main objective of this study was to build up a lithological profile and to use the data in order to improve the knowledge about the local geology (Quaternary deposits). Lithological information at shallow depth is generally used to better understand the local site effects, known to play an important role in modifying the intensity of ground shaking. The Quaternary sediments of Ramnicu Valcea city were penetrated recently by a 12'' drill hole down to 40 m depth. During the drilling process, the drill cuttings were sampled, labeled, and packed up. Drill cuttings were caught as composite samples that reflect the various lithologies drilled over a 3 m interval. In the last 4 m, the sample rate increase to 1 sample per meter. To do this, the grain size analysis was performed in order to obtain the mass percentages for gravel, sand, mud for each sample. The wet sieve procedure was performed to obtain the textural classes, then the samples have been dried and weighed. The resulted lithology of the borehole profile is given as a mass percentage of different textural classes. The main propose of this study was to obtain lithological information of Ramnicu Valcea seismic site (RMGV) by analysing the drill cuttings. The grain size analysis was chosen method because it was the most reliable method to get lithological information from the soft quaternary sediments high mixed by the drilling process. The results show the mass concentration of gravel, sand, and mud of all sampled intervals from 0 to 40m depth. To see the predominant lithology of analysed samples, the results were plotted in a Folk triangular diagram. The result of the grain size analysis shows that at the upper top and at the bottom part of the profile predominates the gravel and that the middle part is mostly muddy. This study represents the first step in dynamic properties of quaternary sedimentary rocks of Ramnicu Valcea seismic site. The lithological information obtained in this study will be correlated with the future seismic measurements to define a better dynamic and elastic properties of the Quaternary sedimentary strata.

Authors:
Ghiță C., Raicu R., Constantinescu E.G, Moldovan I.A,

Abstract:
The purpose of this study consists in the evaluation of completeness magnitude (Mc), b value spatial variation and seismic energy release in Vrancea crustal seismogenic area, during the period between 1990 and 2021. This parameters are essential for a correct interpretation of seismicity analysis. For the analyses, we have selected from the Romplus seismic catalog (www.infp.ro) the crustal events with depth 0<h<52 Km, and magnitudes 0.1 <Mw <5.4,recorded from 01 January 1990 to 01 March 2021, in the area bordered by 44.5 N - 46.5 N latitude and 26.0 E - 27.5 E longitude.The method we used to calculate Mc is based on the Goodnes of Fit test (GFT).The Mc completeness magnitude parameter is essential in seismology studies and represents the minimum value of the magnitude for which all events in a given region are correctly detected. The b value parameter is calculated taking into account the magnitude of completeness Mc and the average value of the magnitudes of events above the threshold value Mc The seismic energy release in Vrancea zone was calculated in the period 1990-2020 only for crustal depth earthquakes using Mw resulted from the seismic moment (Mo), parameter that measures the overall deformation in the source.

Authors:
Placintă A.O., Borleanu F., Popescu E., Radulian M.

Abstract:
The Vrancea zone, located in Romania, at the sharp bend of the Southeastern Carpathians, is a well-defined seismic region in a continental convergence area with unique properties and generating the most destructive subcrustal earthquakes in Europe. The seismicity is concentrated in a confined, high-velocity, focal volume at 60–200 km depth range. The increasing number and quality of waveforms digitally recorded in the last time by the National Institute for Earth Physics (NIEP) provide the opportunity to better constrain individual source properties and to systematically investigate collective scaling properties. These are fundamental elements to understand the overall seismogenic process in this particular geotectonic area. The purpose of the present paper is to investigate the source parameters and clustering properties for the moderate subcrustal earthquakes recorded between 2016 and 2018 using the Empirical Green’s function and spectral ratios techniques and to see how the results comply with the scaling laws characterizing the Vrancea subcrustal activity. In order to apply the relative deconvolution techniques, we selected a set of Green’s events, recorded between 2016 and 2018, in association with the main events, the largest earthquakes occurred in 2018 in the Vrancea intermediate-depth source: March 14, 2018 (Mw=4.2), April 25, 2018 (Mw=4.1) and October 28, 2018 (Mw=5.5). The application of relative deconvolution techniques shows relatively simple source time function and source spectrum, compatible with a circular source model with homogeneous rupture process. The scaling of seismic moment with source dimension resulted from our analysis on a set of 30 small and moderate earthquakes reproduces well (within inherent errors) the scaling obtained on larger data sets and the theoretical scaling generally adopted for simple source models.

Authors:
Craiu A., Ferrand T.P., Manea E.F., Vrijmoed J.C., Mărmureanu A.

Abstract:
The Vrancea slab, Romania, is a subducted remnant of the Tethyan lithosphere characterized by a significant intermediate-depth seismicity (60&ndash;170 km). A recent study showed a correlation between this seismicity and major dehydration reactions, involving serpentine minerals up to 130 km depth, and high-pressure hydrated talc deeper. Here we investigate the potential link between the triggering mechanisms and the retrieved focal mechanisms of 940 earthquakes, which allows interpreting the depth distribution of the stress field. We observe a switch from horizontal compression to vertical extension between 100 and 130 km depth, where the Clapeyron slope of serpentine dehydration is negative. The negative volume change within dehydrating serpentinized faults, expected mostly sub-horizontal in the verticalized slab, could well explain the vertical extension recorded by the intermediate-depth seismicity. This apparent slab pull is accompanied with a rotation of the main compressive stress, which could favour slab detachments in active subduction zones.

Authors:
Toma-Dănilă D., Țigănescu A., D'Ayala D., Armaș I., Sun L.

Abstract:
Earthquakes can generate a significant number of casualties within seconds, as well as high economic losses. The lack of rapid and coordinated emergency intervention can contribute to much greater losses. In this paper we develop a framework taking advantage of the ArcGis Network Analyst extension, able to account for post-earthquake conditions and reflect travel times. By combining 1) network characteristics with 2) direct seismic damage information, 3) models to determine road obstruction potential, 4) traffic information and time-dependent post-earthquake modeling but also 5) emergency intervention facilities (hospitals or fire stations) and considerations regarding their functional limitations, this framework can provide important support for the management of emergency intervention but also for risk reduction planning. Main results consist of maps showing travel times for various scenarios and moments after an earthquake, inaccessible areas, vital roads for access or an identification of important facilities. As case study we chose Bucharest, one of Europe’s most endangered capitals considering the seismic risk level. The city was and could be considerably affected by earthquakes in the Vrancea Seismic Zone, being characterized by a high number of vulnerable buildings and by one of the greatest typical traffic congestion levels in the world. Compared to previous network studies for Bucharest, the new approach is more complex and customable, providing means for real-time integration and time-dependent analysis. Results, for a worst-case scenario, prove that the risks could be even greater than expected, but also what should be done to mitigate them, such as the construction of a new hospital in the western part of the city, ensuring safe delimited routes for emergency vehicles or expanding the treatment capacity of actual hospitals—some of which also need seismic retrofitting. Results of this study will be integrated in the revised version of the National Conception for Post-Earthquake Response—an operational framework which will lead to risk mitigation through the improvement of post-disaster reaction.

Authors:
Chiaraluce L., Festa G., Bernard P., Caracausi A., Carluccio I., Clinton J., Di Stefano R., Elia L., Evangelidis C., Ergintav S., Jianu O., Kaviris G., Mărmureanu A., Sebela S., Sokos E.

Abstract:
The Near Fault Observatories (NFOs) community is one of the European Plate Observing System (EPOS, http://www.epos-eu.org) Thematic Communities, today consisting of six research infrastructures that operate in regions characterised by high seismic hazard originating from different tectonic regimes. Earthquakes respond to complex natural systems whose mechanical properties evolve over time. Thus, in order to understand the multi-scale, physical/chemical processes responsible for the faulting that earthquakes occur on, it is required to consider phenomena that intersect different research fields, i.e., to put in place multidisciplinary monitoring. Hence, NFOs are grounded on modern and multidisciplinary infrastructures, collecting near fault high resolution raw data that allows generation of innovative scientific products. The NFOs usually complement regional backbone networks with a higher density distribution of seismic, geodetic, geochemical and other geophysical sensors, at surface and sometimes below grade. These dense and modern networks of multi-parametric sensors are sited at and around active faults, where moderate to large earthquakes have occurred in the past and are expected in the future. They continuously monitor the underlying Earth instability processes over a broad time interval. Data collected at each NFO results in an exceptionally high degree of knowledge of the geometry and parameters characterizing the local geological faults and their deformation pattern. The novel data produced by the NFO community is aggregated in EPOS and is made available to a diverse set of stakeholders through the NFO Federated Specific Data Gateway (FRIDGE). In the broader domain of the Solid Earth sciences, NFOs meet the growing expectations of the learning and communication sectors by hosting a large variety of scientific information about earthquakes as a natural phenomenon and a societal issue. It represents the EPOS concept and objective of aggregating and harmonising the European research infrastructures capabilities to facilitate broader scientific opportunity. The NFOs are at the cutting edge of network monitoring. They conduct multidisciplinary experiments for testing multi-sensor stations, as well as realise robust and ultra-low latency, transmission systems that can routinely accommodate temporary monitoring densification. The effort to continuously upgrade the technological efficiency of monitoring systems positions the NFO at the centre of marketing opportunities for the European enterprises devoted to new sensor technology. The NFOs constitute ideal test beds for generating expertise on data integration, creating tools for the next generation of multidisciplinary research, routine data analysis and data visualization. In particular focus is often on near-real time tools and triggering alarms at different levels are tested and implemented, strengthening the cooperation with the Agencies for risk management. NFOs have developed innovative operational actions such as the Testing Centre for Earthquake Early Warning and Source Characterisation (CREW) and detailed fast ground shaking and damage characterization. Complementing the recent growth of modern laboratory and computational models, the NFOs can provide interdisciplinary observations of comparable high resolution to describe the behaviour of fault slip over a vast range of spatial and temporal scales and aiding to provide more accurate earthquake hazard characterizations.

Authors:
Nistor S., Suba N.S., Năstase E., Muntean A.

Abstract:
Daily coordinate time series from Global Navigation Satellite System (GNSS) exhibits important seasonal signals for the horizontal and vertical component. These essential signals must be estimated because they play a very important role in the final estimates, especially for site velocity. The article is analyzing in terms of seasonality and noise, 152 stations from 5 different Continuously Operating Reference Stations (CORS) that have GNSS stations in Romania. The importance of this study is twofold: the first one is given by the relevance of separating various geophysical signals which truthfully reflect critical crustal deformations or the effect of different surface mass loadings, and second, is to compare relatively close stations which are part of two different CORS networks. Due to the fact that the underlying noise of the GNSS station is related to the seasonal signal, using Maximum Likelihood Estimation (MLE) we are able to estimate both seasonal signals, the type of noise and its amplitude for the Romanian GNSS CORS network. The results of the noise analysis show that at low frequencies we have spectral indices that varies between –2 and 0, which reveals that the dominant type of noise is flicker and random noise

Authors:
Oros E., Popa M., Paulescu D., Plăcintă A.O., Ghiță C.

Abstract:
We present a refined and the most complete catalogue of the focal mechanisms for the Intra-Carpathian region of Romania. It contains the high-quality solutions computed for 1217 earthquakes recorded between 1909 and 2018. Primary data gathered from the original seismograms and seismic bulletins have been used to compute the source parameters and focal mechanisms solutions. The focal mechanisms have been obtained using the HASH method by the polarities and S/P amplitudes ratios inversion. Our catalogue provides data necessary for the investigation of the contemporary stress field at different scales with high spatial and temporal resolution. We determined the stress field characteristics through formal inversion of focal mechanisms and also computed the reactivation potential of the active fault systems using the Win&#8209;Tensor program. The stress field is heterogeneous, with SHmax significantly deviating from the first-order stress field direction and also with strong local variations in the stress regime.

Authors:
Apostol B.F.

Abstract:
The tensorial force acting in a localized seismic focus is introduced and the corresponding seismic waves are derived, as solutions of the elastic wave equation in a homogeneous and isotropic body. The deconvolution of the solution for a structured focal region is briefly discussed. The far-field waves are identified as P and S seismic waves. These are spherical-shell waves, with a scissor-like shape, and an amplitude decreasing with the inverse of the distance. The near-field seismic waves are spherical-shell waves, decreasing with the inverse of the squared distance. The amplitudes and the polarizations of the near-field seismic waves are given. The determination of the seismic-moment tensor and the earthquake parameters from measurements of the P and S seismic waves at Earth’s’ surface is briefly discussed. Similarly, the mainshock generated by secondary waves on Earth’s surface is reviewed. The near-field static deformations of a homogeneous and isotropic half-space are discussed and a method of determining the seismic-moment tensor from epicentral near-field (quasi-) static deformations in seismogenic regions is presented.

Authors:
Craiu A., Craiu M., Mihai M., Manea E.F., Mărmureanu A.

Abstract:
The Vrancea seismic zone, located in the bend region of the South-Eastern Carpathians, is a unique area with both crustal and intermediate-depth seismic activity and is known as one of the most active seismic area in Europe. Moderate crustal seismicity is recorded all over the Carpathian region, but the far more intense activity occurs in a small subcrustal seismogenic volume beneath the SE&#8208;bend of the Carpathian arc with about 20&times;50 km lateral and 110 km vertical extent (70&ndash;180 km depth). A unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region. The main focus of this study is to determine the focal mechanisms for events with a magnitude larger than 2.7, between 2005 and 2020 and evaluate the current stress feld along the Vrancea subcrustal region, from the derived fault plane solutions. The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the frst one with the nodal planes, oriented NE&ndash;SW parallel with the Carpathian Arc and the second one with the nodal planes, oriented NW&ndash;SE perpendicular on the Carpathian Arc. The results of stress inversion indicate a dominant thrust faulting style, with an average stress regime index of 2.87. The stress pattern shows similar partitioning with vertical extension in the slab and no preferred orientation in the overlying crust, showing a transition regime from the extensional regime in the Moesian Platform to the compressional regime in the Vrancea subcrustal zone.

Authors:
Mărmureanu G., Cioflan C.O., Apostol B.F.

Abstract:
The seismic response of the ground motion is analysed using processed recordings and related spectral characteristics. The analysis is carried out for few representative different sites, with different geological local conditions. Data used are recordings from the last strongest seismic events (1986, August 30, Mw = 7.1, 1990, May 30, Mw = 6.9 and 1990, May 31, Mw=6.4). The approach used herein to assess the particular features of the seismic effects could open a new perspective in microzoning and risk studies. In the context of Vrancea-intermediate depth seismicity, whose effects are encountered at long epicentral distances, the choice of these sites is fully justified. Therefore the paper intends to focus on the particularities in the site effects that occur due to the sedimentary deposits&rsquo; oscillation under strong seismic ground motion for different areas. The spectral amplification factors are introduced in order to have a quantitative representation with respect to the variability of site effects.

Authors:
Toma-Dănilă D., Tătaru D., Năstase E.

Abstract:
In order for strategies in seismic risk mitigation to be effective, they need to consider both the level of risk but also the needs and attitude of people subjected to the desired change. Questionnaires are one of the most common tools to assess the perception and preparedness of people to earthquakes, however we found that many designs and interpretations are limited to the obvious remarks and are not conceived or analyzed in ways enabling the determination of sociological profiles and geospatial patterns. Through this paper we show the potential of new questionnaire-based approaches and interpretations, highlighting aspects such as i) how well prepared in case of an earthquake people think and actually are depending also on their age, ii) does living in an area with high hazard values influences perception of risk and what is the difference between risk in locality versus individual risk, iii) is there a difference between how people with earthquake knowledge would behave in case of having an earthquake early warning solution compared to people with less knowledge or iv) which ways of communicating risk is considered more appropriate for different age groups. As input, we use more than 410 responses collected for most of Romania (out of which around half are for Bucharest Area), through two easy-to-fill online questionnaires: one focusing on earthquake perception as well as the level of knowledge and vision toward preparedness strategies, and another shaped as a checklist test, related to the individual level of preparedness.

Authors:
Bălan S.F., Apostol B.F., Țigănescu A.

Abstract:
The paper presents the seismic monitoring network of the TURNKey Project (Towards more Earthquake-resilient Urban Societies through a Multi-sensor-based Information System enabling Earthquake Forecasting, Early Warning and Rapid Response Actions) in Bucharest. TURNkey aims to contribute to the mitigation of earthquake risks through European and global scientific collaborations. To reach its objectives the project brings together a strong multidisciplinary team of experts geophysicists/seismologists, geologists, engineers, disaster risk managers and sociologists) from 21 partner institutions covering 10 European countries. &ldquo;Testbed 1&rdquo; (Bucharest) is described in the paper, with its five monitored locations and the deployed seismic sensors and GNSS. The choice of monitored buildings is based upon the characteristics of the design code used in their construction. The paper considers the possible influence of local conditions at the sites of the monitored buildings.

Authors:
Özcebe A.G., Țigănescu A., Ozer E., Negulescu C., Galiana-Merino J.J., Tubaldi E., Toma-Dănilă D., Molina S., Kharazian A., Bozzoni F., Borzi B., Bălan S.F.

Abstract:
The Internet of things concept empowered by low-cost sensor technologies and headless computers has upscaled the applicability of vibration monitoring systems in recent years. Raspberry Shake devices are among those systems, constituting a crowdsourcing framework and forming a worldwide seismic network of over a thousand nodes. While Raspberry Shake devices have been proven to densify seismograph arrays efficiently, their potential for structural health monitoring (SHM) is still unknown and is open to discovery. This paper presents recent findings from existing buildings located in Bucharest (Romania) equipped with Raspberry Shake 4D (RS4D) devices, whose signal recorded under multiple seismic events has been analyzed using different modal identification algorithms. The obtained results show that RS4D modules can capture the building vibration behavior despite the short-duration and low-amplitude excitation sources. Based on 15 RS4D device readings from five different multistorey buildings, the results do not indicate damage in terms of modal frequency decay. The findings of this research propose a baseline for future seismic events that can track the changes in vibration characteristics as a consequence of future strong earthquakes. In summary, this research presents multi-device, multi-testbed, and multi-algorithm evidence on the feasibility of RS4D modules as SHM instruments, which are yet to be explored in earthquake engineering.

Authors:
Țigănescu A., Grecu B., Neagoe C., Toma-Dănilă D., Tătaru D., Ionescu C., Bălan S.F.

Abstract:
The PREVENT project's main objective is to systemize the research outcomes and the computational capabilities in order to develop, implement and test an integrated dynamic platform for civil structures monitoring. The present paper focuses on the description of the instrumentation setup, dataflow, the platform architecture and preliminary results for the most recent Vrancea intermediate-depth earthquakes. The expected outcomes of the project will consist of the first high-quality database recorded on structures and will provide a valuable tool to the research community, earthquake engineering community, authorities and stakeholders as well as to teachers and students, for educational purposes.

Authors:
Petrescu L., Borleanu F., Plăcintă A.O.

Abstract:
The Black Sea is the largest European back-arc basin connected to the subduction and final closure of the Tethys ocean. Its origin and type of crust are widely debated, with contrasting views suggesting it is either a relic of Paleotethys or a rifted back-arc basin formed within the thick and cold Precambrian lithosphere. To investigate the structure of this atypical intra-continental basin, we constructed the highest resolution seismic tomography of the region using the latest techniques of probabilistic inversion of ambient noise data recorded at seismic stations around the sea. Our results indicate the presence of thinned continental crust beneath the basin, likely of Precambrian lithospheric origin, thus invalidating the existence of either a relic Paleotethys fragment or younger oceanic crust. Extension and rifting probably exploited pre-existing sutures, but the rheologically strong lithosphere resisted transition to seafloor spreading. Seismic anisotropy shows complex paleo-deformational imprints within the crust and upper mantle related to the closure of Tethys. Extension caused by subduction roll-back generated anisotropic lithospheric fabric parallel to the rifting axis within the thinnest sections of the crust in the western basin. The eastern part developed on a distinct lithospheric domain that preserves paleo-extension anisotropy signatures in the form of lower crustal viscous deformation. Further south, anisotropy orients along the Balkanide-Pontide collisional system that records the final stages of Neotethys closure. Our results place key constraints on the type of deformations that occurred throughout the Tethyan realm, with fundamental implications for the development and evolution of back-arc basins and continental break-up.

Authors:
Mihai A., Roban R.D., Toader V.E., Lingvay I., Ciogescu O.

Abstract:
In absence of core samples and open-hole well-log data, the broken bits of rock removed from the borehole during the drilling process represent in many cases the only lithological data that is recovered from a well. The main objective of this study was to build up a lithological profile and to use the data in order to improve the knowledge about the local geology (Quaternary deposits). Lithological information at shallow depth is generally used to better understand the local site effects, known to play an important role in modifying the intensity of ground shaking. The Quaternary sediments of Ramnicu Valcea city were penetrated recently by a 12'' drill hole down to 40 m depth. During the drilling process, the drill cuttings were sampled, labeled, and packed up. Drill cuttings were caught as composite samples that reflect the various lithologies drilled over a 3 m interval. In the last 4 m, the sample rate increase to 1 sample per meter. To do this, the grain size analysis was performed in order to obtain the mass percentages for gravel, sand, mud for each sample. The wet sieve procedure was performed to obtain the textural classes, then the samples have been dried and weighed. The resulted lithology of the borehole profile is given as a mass percentage of different textural classes. The main propose of this study was to obtain lithological information of Ramnicu Valcea seismic site (RMGV) by analysing the drill cuttings. The grain size analysis was chosen method because it was the most reliable method to get lithological information from the soft quaternary sediments high mixed by the drilling process. The results show the mass concentration of gravel, sand, and mud of all sampled intervals from 0 to 40m depth. To see the predominant lithology of analysed samples, the results were plotted in a Folk triangular diagram. The result of the grain size analysis shows that at the upper top and at the bottom part of the profile predominates the gravel and that the middle part is mostly muddy. This study represents the first step in dynamic properties of quaternary sedimentary rocks of Ramnicu Valcea seismic site. The lithological information obtained in this study will be correlated with the future seismic measurements to define a better dynamic and elastic properties of the Quaternary sedimentary strata.

Authors:
Mărmureanu A., Ionescu C., Grecu B., Toma-Dănilă D., Țigănescu A., Neagoe C., Toader V.E., Craifaleanu I.G., Dragomir C.S., Meiţă V., Liashchuk O.I., Dimitrova L., Ilieş I.

Abstract:
The aim of this article is to analyze the background, current status, and outlook of seismic monitoring products and services in Bulgaria, Moldova, Romania, and Ukraine. These countries manage seismic networks that contribute to the European Integrated Data Archive node in the framework of the bservatories and Research Facilities for European Seismology, which represents a collaborative effort in coordinating observational seismology across the European region through the collection, archiving, and dissemination of seismic waveform data, metadata, and related products. All of the aforementioned countries share a common threat: strong earthquakes occurring in the Vrancea area located in central-eastern Romania at intermediate depths (usually in the 60–180 km interval). Events such as the ones on 10 November 1940 and 4 March 1977 generated high damage in Romania, northern Bulgaria, and Moldova. In addition to Vrancea, crustal earthquakes in areas such as Shabla or Dulovo can lead to cross-border damage. Therefore, understanding the way national seismic networks are distributed, how they cooperate, and the products and services that they provide in (near) real time and their terms is of significant interest in the context of necessary hazard harmonization and joint emergency intervention and risk mitigation actions.

Authors:
Shimojo K., Enescu B., Yagi Y., Takeda T.

Abstract:
The 2011 magnitude (M) 9.0 Tohoku-oki earthquake was followed by seismicity activation in inland areas throughout Japan. An outstanding case is the M6.2 Northern Nagano earthquake, central Japan, occurred 13-h after the megathrust event, approximately 400 km away from its epicenter. The physical processes relating the occurrence of megathrust earthquakes and subsequent activation of relatively large inland earthquakes are not well understood. Here we use waveform data of a dense local seismic network to reveal with an unprecedented resolution the complex mechanisms leading to the occurrence of the M6.2 earthquake. We show that previously undetected small earthquakes initiated along the Nagano earthquake source fault at relatively short times after the Tohoku-oki megathrust earthquake, and the local seismicity continued intermittently until the occurrence of the M6.2 event, being likely 'modulated' by the arrival of surface waves from large, remote aftershocks off-shore Tohoku. About 1-h before the Nagano earthquake, there was an acceleration of micro-seismicity migrating towards its hypocenter. Migration speeds indicate potential localized slow-slip, culminating with the occurrence of the large inland earthquake, with fluids playing a seismicity-activation role at a regional scale.

Authors:
Crowley H., Despotaki V., Silva V., Dabbeek J., Romao X., Pereira N., Castro J.M., Daniell J., Veliu E., Bilgin H., Adam C., Deyanova M., Ademovic N., Atalic J., Riga E., Karatzetou A., Bessason B., Shendova V., Țigănescu A., Toma-Dănilă D., Zugic Z., Akkar S., Hancilar U.

Abstract:
As part of the development of a European Seismic Risk Model 2020 (ESRM20), the spatial and temporal evolution of seismic design across Europe has been studied in order to better classify reinforced concrete buildings (which represent more than 30% of the approximately 145 million residential, commercial and industrial buildings in Europe) and map them to vulnerability models based on simulated seismic design. This paper summarises the model that has been developed to assign the years when different seismic design levels (low code, moderate code and high code) were introduced in a number of European countries and the associated lateral forces that were specified spatially within each country for the low and moderate codes for typical reinforced concrete mid-rise buildings. This process has led to an improved understanding of how design regulations evolved across Europe and how this has impacted the vulnerability of the European residential building stock. The model estimates that similar to 60% of the reinforced concrete buildings in Europe have been seismically designed, and of those buildings similar to 60% have been designed to low code, similar to 25% to moderate code and 15% to high code. This seismic design model aims at being a dynamic source of information that will be continuously updated with additional feedback from local experts and datasets. To this end, all of the data has been made openly available as shapefiles on a GitLab repository.

Authors:
Ferrand T.P., Manea E.F.

Abstract:
Vrancea, Eastern Romania, presents a significant intermediate-depth seismicity, between 60 and 170 km depth, i.e. pressures from 2 to 6.5 GPa. A debate has been lasting for decades regarding the nature of the seismic volume, which could correspond to the remnant of a subducted slab of Tethyan lithosphere or a delamination of the Carpathians lithosphere. Here we compile the entire seismicity dataset (&#8776; 10,000 events with 2 &#8804; Mw &#8804; 7.9) beneath Vrancea for P > 0.55 GPa (> 20 km) since 1940 and estimate the pressure and temperature associated with each hypocenter. We infer the pressure and temperature, respectively, from a depth-pressure conversion and from the most recent tomography-based thermal model. Pressure&ndash;temperature diagrams show to what extent these hypocentral conditions match the thermodynamic stability limits for minerals typical of the uppermost mantle, oceanic crust and lower continental crust. The stability limits of lawsonite, chloritoid, serpentine and talc minerals show particularly good correlations. Overall, the destabilization of both mantle and crustal minerals could participate in explaining the observed seismicity, but mantle minerals appear more likely with more convincing correlations. Most hypocentral conditions match relatively well antigorite dehydration between 2 and 4.5 GPa; at higher pressures, the dehydration of the 10-&Aring; phase provides the best fit. We demonstrate that the Vrancea intermediate-depth seismicity is evidence of the current dehydration of an oceanic slab beneath Romania. Our results are consistent with a recent rollback of a W-dipping oceanic slab, whose current location is explained by limited delamination of the continental Moesian lithosphere between the Tethyan suture zone and Vrancea.

Authors:
Plăcintă A.O., Borleanu F., Popescu E., Radulian M.

Abstract:
The Vrancea zone, located in Romania, at the sharp bend of the Southeastern Carpathians, is a well-defined seismic region in a continental convergence area with unique properties and generating the most destructive subcrustal earthquakes in Europe. The seismicity is concentrated in a confined, high-velocity, focal volume at 60-200 km depth range. The increasing number and quality of waveforms digitally recorded in the last time by the National Institute for Earth Physics (NIEP) provide the opportunity to better constrain individual source properties and to systematically investigate collective scaling properties. These are fundamental elements to understand the overall seismogenic process in this particular geotectonic area. The purpose of the present paper is to investigate the source parameters and clustering properties for the moderate subcrustal earthquakes recorded between 2016 and 2018 using the Empirical Green's function and spectral ratios techniques and to see how the results comply with the scaling laws characterizing the Vrancea subcrustal activity. In order to apply the relative deconvolution techniques, we selected a set of Green's events, recorded between 2016 and 2018, in association with the main events, the largest earthquakes occurred in 2018 in the Vrancea intermediate-depth source: March 14, 2018 (Mw=4.2), April 25, 2018 (Mw=4.1) and October 28, 2018 (Mw=5.5). The application of relative deconvolution techniques shows relatively simple source time function and source spectrum, compatible with a circular source model with homogeneous rupture process. The scaling of seismic moment with source dimension resulted from our analysis on a set of 30 small and moderate earthquakes reproduces well (within inherent errors) the scaling obtained on larger data sets and the theoretical scaling generally adopted for simple source models.

Authors:
Ghiță C., Raicu R.D., Constantinescu E., Moldovan I.A.

Abstract:
The purpose of this study consists in the evaluation of completeness magnitude (Mc), b value spatial variation and seismic energy release in Vrancea crustal seismogenic area, during the period between 1990 and 2021. This parameters are essential for a correct interpretation of seismicity analysis. For the analyses, we have selected from the Romplus seismic catalog (www.infp.ro) the crustal events with depth 0<h<52 Km, and magnitudes 0.1 <Mw <5.4,recorded from 01 January 1990 to 01 March 2021, in the area bordered by 44.5 N - 46.5 N latitude and 26.0 E - 27.5 E longitude.The method we used to calculate Mc is based on the Goodnes of Fit test (GFT).The Mc completeness magnitude parameter is essential in seismology studies and represents the minimum value of the magnitude for which all events in a given region are correctly detected. The b value parameter is calculated taking into account the magnitude of completeness Mc and the average value of the magnitudes of events above the threshold value Mc The seismic energy release in Vrancea zone was calculated in the period 1990-2020 only for crustal depth earthquakes using Mw resulted from the seismic moment (Mo), parameter that measures the overall deformation in the source.

Authors:
Mihai A,., Roban R.D., Toader V.E., Lingvay I., Ciogescu O.

Abstract:
In absence of core samples and open-hole well-log data, the broken bits of rock removed from the borehole during the drilling process represent in many cases the only lithological data that is recovered from a well. The main objective of this study was to build up a lithological profile and to use the data in order to improve the knowledge about the local geology (Quaternary deposits). Lithological information at shallow depth is generally used to better understand the local site effects, known to play an important role in modifying the intensity of ground shaking. The Quaternary sediments of Râmnicu Vâlcea city were penetrated recently by a 12'' drill hole down to 40 m depth. During the drilling process, the drill cuttings were sampled, labeled, and packed up. Drill cuttings were caught as composite samples that reflect the various lithologies drilled over a 3 m interval. In the last 4 m, the sample rate increase to 1 sample per meter. To do this, the grain size analysis was performed in order to obtain the mass percentages for gravel, sand, mud for each sample. The wet sieve procedure was performed to obtain the textural classes, then the samples have been dried and weighed. The resulted lithology of the borehole profile is given as a mass percentage of different textural classes. The main propose of this study was to obtain lithological information of Râmnicu Vâlcea seismic site (RMGV) by analysing the drill cuttings. The grain size analysis was chosen method because it was the most reliable method to get lithological information from the soft quaternary sediments high mixed by the drilling process. The results show the mass concentration of gravel, sand, and mud of all sampled intervals from 0 to 40m depth. To see the predominant lithology of analysed samples, the results were plotted in a Folk triangular diagram. The result of the grain size analysis shows that at the upper top and at the bottom part of the profile predominates the gravel and that the middle part is mostly muddy. This study represents the first step in dynamic properties of quaternary sedimentary rocks of Râmnicu Vâlcea seismic site. The lithological information obtained in this study will be correlated with the future seismic measurements to define a better dynamic and elastic properties of the Quaternary sedimentary strata.

Authors:
Toader V.E., Mihai A., Circiumaru G., Ciogescu O., Voina A., Lingvay I.

Abstract:
An assessment of the tectonic activity in V&acirc;lcea-F&acirc;g&acirc;ra&#351;-C&acirc;mpulung seismic area is presented, with a direct impact on the power facilities operational safety - especially of the numerous hydropower plants in this area. The analysis of the acquired data revealed that the seismic activity in this mountainous area (with a high hydropower potential) shows an intensifying trend. As the seismic hazard is significant, in order to increase the operational safety of energy equipment and installations, to reduce the damage caused by crustal earthquakes specific to the area, it is strongly recommended that energy equipment and installations to be provided with complex adequate protection systems as warning systems based on local assessment of seismic events.

Authors:
Zheng Y., Enescu B., Zhuang J., Yu C.

Abstract:
Missing early aftershocks following relatively large or moderate earthquakes can cause significant bias in the analysis of seismic catalogs. In this paper, we systematically address the aftershock missing problem for five earthquake sequences associated with moderate-size events that occurred inland Japan, by using a stochastic replenishing method. The method is based on the notion that if a point process (e.g., earthquake sequence) with time-independent marks (e.g., magnitudes) is completely observed, it can be transformed into a homogeneous Poisson process by a bi-scale empirical transformation. We use the Japan Meteorological Agency (JMA) earthquake catalog to select the aftershock data and replenish the missing early events using the later complete part of each aftershock sequence. The time windows for each sequence span from 6 months before the mainshock to three months after. The semi-automatic spatial selection uses a clustering method for the epicentral selection of earthquakes. The results obtained for the original JMA catalog and replenished datasets are compared to get insight into the biases that the missing early aftershocks may cause on the Omori-Utsu law parameters’ estimation, characterizing the aftershock decay with time from the mainshock. We have also compared the Omori-Utsu law parameter estimates for two datasets following the same mainshock; the first dataset is the replenished sequence, while the second dataset has been obtained by waveform-based analysis to detect early aftershocks that are not recorded in the JMA catalog. Our results demonstrate that the Omori-Utsu law parameters estimated for the replenished datasets are robust with respect to the threshold magnitude used for the analyzed datasets. Even when using aftershock time windows as short as three days, the replenished datasets provide stable Omori-Utsu law parameter estimations. The p-values for all the analyzed sequences are about 1.1 and c-values are significantly smaller compared to those of original datasets. Our findings prove that the replenishment method is a fast, reliable approach to address the missing aftershock problem.

Authors:
Bălă A., Toma-Dănilă D.

Abstract:
The contribution of local site effects to seismic hazard is significant in cities located on thick stack of loose Quaternary layers of sediments such as Bucharest City. Here, strong-motion recordings of major intermediate-depth Vrancea earthquakes in 1986 and 1990, as well as the disastrous effects of previous major earthquakes (in 1940 or 1977) proved the necessity and importance of microzonation maps not only for new building design, but also for a great part of Bucharest old buildings stock, which is in a critical need for urgent retrofitting. Some studies emphasized the conclusion that mean shear-wave velocities (Vs) corresponding to the main 7 geological layers in the Bucharest underground: i) are important and must be known until deeper depth of 100-150 m, making Vs-30 an insufficient and obsolete proxy for the explanation of spectral acceleration peaks at surface (Bala et al., 2014); ii) in surface the values of Vs may vary considerably across the city in just a few hundreds of meters.

Authors:
Lenhardt W.A., Pesaresi D., Zivi M., Costa G., Fiket T., Bondar I., Duni L., Spacek P., Dimitrova L., Neagoe C., Malyskyy D., Csicsay K.

Abstract:
The complex tectonic setup of eastern Europe resulting in strong spatial variations of the local seismic hazard caused relevant institutions of neighboring countries to form a research cooperation to ease seismological research cooperations across borders. Here,we briefly introduce the original and newCentral and Eastern Europe Earthquake Research Network (CE3RN) parties, with a synthesis of thecommon results achieved so far and an indication of possible future developments. Since the formal establishment of CE3RN, severalcommon projects have been initiated, such as the SeismoSAT Project for the seismic data center connection over satellite and the Historical and Recent Earthquakes in Italy and Austria Project, both funded by the European Union INTERREG Italy Austria Program. The most recent 22 March 2020 earthquake near Zagreb, resulting in considerable damage in the capital of Croatia, demonstrated the importance of fast data exchange, thus facilitating reliable analysis of the earthquake. In addition, a recent breakdown of data lines in Austria demonstrated the usefulness of alternative data transmission via satellite.

Authors:
Poiată N., Tătaru D., Borleanu F., Grecu B.

Abstract:
The intermediate-depth seismicity from Vrancea seismic region in Romania represents the main source of seismic hazard for Romania and neighbouring countries, with the most recent largest events (M 7.7 and 7.4) known to have caused significant and widespread destruction. The particular characteristics of Vrancea seismogenic volume that fall into category of, so called, “seismic nests”, make it as well of great scientific interest in seismology. In this study we present first results evaluating the performance and capability of an automated network-based full-waveform earthquake detection and location scheme for building a detailed view of seismic activity in space and time with the focus on the intermediate-depth earthquakes from Vrancea seismic source Romania. We make use of case-specific synthetic examples for testing the parameters of the detection and location scheme and analysing the influence of station configuration on the accuracy of events location.

Authors:
Năstase E., Muntean A., Jecu M., Radulescu V., Stanciu I., Drăgășanu C., Ion M., Dimitriu S.

Abstract:
The latest years reveal to us the necessity and the interest to develop an integrated research platform to improve skills in answering fundamental scientific questions in the field of Earth sciences and questions in the socioeconomic field related to geo-hazards and geo-resources at the European level, a platform known by EPOS - European Plate Observing System. Main objectives such as the implementation of thematic services (TCS) for different communities in EPOS, the development of integrated services (ICS) for interoperability, data management and access to services, ensuring the long-term financial and legal sustainability of EPOS - ERIC and implementing services lead to the harmonization of EPOS implementations with the national strategy. As a result, many European states mirror the EPOS platform at the national level and Romania is one of them (Integrated thematic services in the field Earth Observation - A national platform for innovation &ndash; SETTING). An electronic research infrastructure was developed for data integration of products and services and offered to users. This contributed to building a community for Earth Sciences by promoting cooperation with complementary projects in geosciences (Geo, ICT, and environmental sciences) and offering services to different users and authorities.

Authors:
Mateciuc N.D., Bălă A.

Abstract:
The present paper aims to analyze the state of crustal deformation in the Vrancea area using GPS measurement data. Unlike previous approaches that used station networks, uniaxial deformations method on profiles has now been used. A brief description of the extended Vrancea network was made, whose nodes were used to draw the measurement alignments. For each subnet Northern Vrancea and Southern Vrancea respectively, separate alignments were drawn, the analysis being carried out for each subnet separately. The analysis takes into consideration 21 alignments, 8 in the Northern Vrancea subnet and 13 in Southern Vrancea subnet. The results are presented in the form of result tables, in which the uniaxial strains and the variation of the angle with respect to the North direction at the two moments of the determinations, t1 and t2 were determined. For each measurement alignment, a graphic representation that contains all the calculated elements was made. The conclusions refer to the characteristics of the two subnets in terms of calculated values, to the strain magnitudes and to their possible connection with the local fault system.

Authors:
Adina V., Popa M., Ionescu C., Paulescu D.

Abstract:
The science of seismology is relatively new. In the last 100 years, important milestones were achieved both in the understanding of the geological particularities which influences the earthquakes occurrences and in the development of seismological instruments. In Romania, the seismological service was founded at the end of XIX century by the initiative of some dedicated researchers in the field of astronomy, geosciences, mathematics and physics. In 1902 in Romania there were two seismological services at Bucharest and Timisoara. Through hard work and devotement, these earthquake study initiatives extended in organizing the first seismic stations in Romania. In time, the seismic stations activity was organized in a more durable context, by creating the Romanian Seismic Network. Nowadays, the Romanian Seismic Network has over 200 stations both in Romania and in neighboring countries, fully equipped with digital instruments of high precision.

Authors:
Tolea A., Grecu B., Neagoe C.

Abstract:
In this paper, we analyze eleven years of continuous data (January 2010–December 2020) from 119 stations of the Romanian Seismic Network using the power spectral densities and their corresponding probability density functions (PSD PDF) in order to construct a new version of the Romanian PSD PDF mode low-noise model (RONM).

Authors:
Dinescu R., Ghica D., Popa M., Munteanu I., Radulian M.

Abstract:
The Romanian Seismic Catalogue has been contaminated in the last period with events from anthropic sources, especially in the regions with active quarry activities. In this paper, we chose as the study area the Targu-Jiu zone, located in Southern Carpathians, where the National Seismic Network (RSN) recorded both crustal events and quarry blasts. For discrimination purposes, the events recorded in a 10-km radius circle around each quarry will be analysed through several methods, to properly identify the quarry blasts. Thus, statistical methods are used, as well as the cross-correlation technique for the recordings of Gura Zlata (GZR) seismic station. In the first stage, a statistical analysis of the events recorded in the quarries area is performed, based on depth intervals, magnitude, working hours and days of the week. The spectrogram analyses are investigated with the DTK-GPMCC and DTK-DIVA extended CTBTO NDC-in-a-box packages developed by the CEA-DASE. The events identified on the seismic recordings are used as templates for the cross-correlation method applied to the events recorded by the GZR for the 2010–2020 time interval.

Authors:
Apostol B.F.

Abstract:
Bath’s empirical law is derived from the magnitude-difference statistical distribution of earthquake pairs. The pair (two-event, bivariate) distribution related to earthquake correlations is presented. The single-event distribution of dynamically-correlated earthquakes is derived, by means of the geometric-growth model of energy accumulation in the focal region. It is shown that the dynamical correlations may account, at least partially, for the roll-off effect in the Gutenberg-Richter distributions. The extension of the magnitude difference to negative values (by observing the order of the members of the pair) leads to a vanishing mean value of the magnitude difference and to the standard deviation as a measure of its variations. It is suggested that the standard deviation of the magnitude difference is the average difference in magnitude between the main shock and its largest aftershock (foreshock), thus providing an insight into the nature and the origin of Bath’s law. Earthquake purely statistical correlations and deterministic time-magnitude correlations of the accompanying seismic activity are also presented.

Authors:
Toma-Dănilă D., Țigănescu A., Cioflan C.O., Ionescu C., Bălan S.F.

Abstract:
In 2011, the Near Real-Time System for Estimating the Seismic Damage in Romania (SeisDaRo), became operational at the National Institute for Earth Physics, Romania. This system based on the SELENA software, PAGER and ShakeMap methodologies provides, within minutes after an earthquake with magnitude ≥ 3, loss estimates in terms of affected buildings and population, at city level or even smaller. Up to now, three subsequent versions have been developed and implemented - each one being scientifically and also technically improved. 10 years apart after the first version is a good moment to document the lessons learned during SeisDaRo’s exploitation, its effective contribution to seismic risk evaluation in Romania and also its potential in the management of emergency situations. As new recent international projects such as TURNkey (with the capital city - Bucharest as testbed) or REDACt (with Constanta City as testbed) are progressing, we also present how these will contribute to improved rapid earthquake loss estimations in Romania, along with a new version of SeisDaRo that will take advantage of the new developments and research initiatives at national, European and worldwide level.

Authors:
Bălan S.F., Apostol B.F., Țigănescu A.

Abstract:
Some buildings need special attention in attempting to protect them against strong seismic movements. Seismic isolation comes as a suitable solution to protect the integrity of the construction. For this accomplishment are needed some thorough data about the dynamic characteristics of the structure and site specificity. The characteristics of the buildings can be found from either design data, or from subsequent measurements on its structure. The study of seismic waves has become a design criterion in advanced seismic codes, using design spectra compatible with local conditions differentiated on qualitative stratigraphic description and quantitative waves velocity-based criteria. The results of the later important geophysical measurement campaigns are described and used in this work. To identify whether seismic isolation for buildings is efficient in an earthquakes-prone environment, very important is the analysis of the location they are, or will be. One of the most important elements to be evaluated is the natural period of the site. The conditions for an efficient seismic isolation are presented and discussed with examples. In the paper are also described the different types of seismic isolated structures in Bucharest, and the reason for selecting them.

Authors:
Bălă A., Radulian M., Toma-Dănilă D.

Abstract:
Vrancea seismogenic zone in the South-Eastern Carpathians is characterized by localized intermediate-depth seismicity. Due to its complex geodynamics and large strain release, Vrancea represents a key element in the Carpatho-Pannonian system. Data from a recently compiled catalogue of fault plane solutions (REFMC) are inverted to evaluate stress regime in Vrancea on depth. A single predominant downdip extensive regime is obtained in all considered clusters, including the crustal layers located above the Vrancea slab. The prevalent stress regime confirms previous investigations and requires some mantle-crust coupling. The S3 principal stress is close to vertical, while S1 and S2 are horizontal, oriented perpendicularly and respectively tangentially to the Carpathians Arc bend. This configuration is present at any depth level. According to seismicity patterns, there are two main active segments in the Vrancea intermediate-depth domain, at 55 – 105 km and 105 – 180 km, both able to generate major events. The configuration of the tectonic stresses as resulted from inversion is similar in both segments. Also, high fault instability (I > 0.95) is characterizing the segments. The only notable difference is given by the friction and stress ratio parameters which drop down in the bottom segment from μ = 0.95 to μ = 0.55 and from R = 0.51 to R = 0.29. This variation is attributed to possible weakening processes activated below 100 km depth and can explain the intensification of seismicity production as earthquake rate and average energy release in the lower segment versus the upper segment.

Authors:
Lanzano G., Luzi L., Cauzzi C., Bienkowski J., Bindi D., Clinton J., Cocco M., D'Amico M., Douglas J., Faenza L., Felicetta C., Gallovic F., Giardini D., Ktenidou O.J., Lauciani V., Manakou M., Mărmureanu A., Maufroy E., Michelini A., Ozener H., Puglia R., Rupakhety R., Russo E., Shahvar M., Sleeman R., Theodoulidis N.

Abstract:
Strong groundmotion records and free open access to strong-motion data repositories are fundamental inputs to seismology, engineering seismology, soil dynamics, and earthquake engineering science and practice. This article presents the current status and outlook of the Observatories and Research Facilities for European Seismology (ORFEUS) coordinated strong-motion seismology services, namely the rapid raw strong-motion (RRSM) and the engineering strong-motion (ESM) databases and associated web interfaces andwebservices.Wecompare and discuss the role and use of these two systems using theMw 6.5 Norcia (Central Italy) earthquake that occurred on 30 October 2016 as an example of a well-recorded earthquake that triggered major interest in the seismological and earthquake engineeringcommunities. The RRSM is a fully automated system for rapid dissemination of earthquake shaking information, whereas the ESM provides qualitychecked, manually processed waveforms and reviewed earthquake information. The RRSM uses only data from the European Integrated Waveform Data Archive, whereas the ESM also includes offline data from other sources, such as the ITalian ACcelerometric Archive (ITACA). Advanced software tools are also included in the ESM to allow users to process strong-motion data and to select ground-motion waveform sets for seismic structural analyses. The RRSM and ESM arecomplementary services designed for a variety of possible stakeholders, ranging fromscientists to the educated general public. The RRSM and ESM are developed, organized, and reviewed by selected members of the seismologicalcommunity in Europe, including strong-motion data providers and expert users. Global access and usage of the data is encouraged. The ESM is presently the reference database for harmonized seismic hazard and risk studies in Europe. ORFEUS strong-motion data are open, "Findable, Accessible, Interoperable, and Reusable," and accompanied by licensing information. The users are encouraged to properly cite the data providers, using the digital object identifiers of the seismic networks.

Authors:
Strollo A., Cambaz D., Clinton J., Danecek P., Evangelidis C.P., Mărmureanu A., Ottemöller L., Pedersen H., Sleeman R., Stammler K., Armbruster D., Bienkowski J., Boukouras K., Evans P.L., Fares M., Neagoe C., Heimers S., Heinloo A., Hoffmann M., Kaestli P., Lauciani V., Michalek J., Muhire E.O., Ozer M., Pălăngeanu L., Pardo C., Quinteros J., Quintiliani M., Salvador J.A.J., Schaeffer J., Schloemer A., Triantafyllis N.

Abstract:
The European Integrated Data Archive (EIDA) is the infrastructure that provides access to the seismic‐waveform archives collected by European agencies. This distributed system is managed by Observatories and Research Facilities for European Seismology. EIDA provides seamless access to seismic data from 12 data archives across Europe by means of standard services, exposing data on behalf of hundreds of network operators and research organizations. More than 12,000 stations from permanent and temporary networks equipped with seismometers, accelerometers, pressure sensors, and other sensors are accessible through the EIDA federated services. A growing user base currently counting around 3000 unique users per year has been requesting data and using EIDA services. The EIDA system is designed to scale up to support additional new services, data types, and nodes. Data holdings, services, and user numbers have grown substantially since the establishment of EIDA in 2013. EIDA is currently active in developing suitable data management approaches for new emerging technologies (e.g., distributed acoustic sensing) and challenges related to big datasets. This article reviews the evolution of EIDA, the current data holdings, and service portfolio, and gives an outlook on the current developments and the future envisaged challenges.

Authors:
Ionescu C., Popa M., Neagoe C., Ghica D.V.

Abstract:
Constantin Ionescu, Mihaela Popa, Cristian Neagoe and Daniela Veronica Ghica report on seismic monitorig at the National Institute for Earth Physics in Măgurele, Romania, for the Summary of the Bulletin of the ISC.

Authors:
Țigănescu A., Toma-Dănilă D., Grecu B., Craifăleanu I.G., Bălan S.F., Dragomir C.S.

Abstract:
The management of emergency situations generated by natural or man-made disasters is a worldwide critical task for both public and private entities. In Romania, seismic hazard represents one of the most dangerous threats, in terms of potential physical and socio-economic losses. In recent years, taking advantage of the new technology developments and increase of the computational power, significant improvements have been done for seismic risk mitigation, using automatic systems and real-time data. There are two main institutions that perform real-time seismic monitoring of structures in Romania: INFP and URBAN-INCERC. A system for rapid damage and loss assessment (Seisdaro) is currently running at INFP, using post-earthquake generated ShakeMaps, while URBAN-INCERC is in the process of implementing a structural health monitoring system for instrumented buildings in its network, based on the ARTeMIS software. A brief history on the evolution of seismic monitoring of building structures and rapid seismic loss assessment in Romania will be presented. The paper also covers general lessons learned from previous earthquakes that affected the country, data regarding past and present exposure datasets, country-specific fragility functions and various methods and algorithms used for structural health monitoring over the time. Through international and national projects, constant improvements have been done regarding the seismic monitoring of structures and loss estimation. The roadmap for future developments involving the main institutions in charge of the seismic risk reduction, including research, academia and authorities, will be also outlined. Finally, given the complex situations revealed by the pandemic and its potential conjunction with other hazards, some reflections are presented about new multi-disciplinary methods and concepts that should be developed, implemented and tested, taking into account more variables such as: social vulnerability, influence of transportation networks and hospital capacities. The validation of these methods should help both private and public entities to increase life safety, to reduce economic losses and downtime.

Authors:
Diaconescu M., Craiu A., Toma-Dănilă D., Constantinescu E.G.

Abstract:
The main purpose of the paper is to highlight the crustal seismicity of the Black Sea, taking into account and the tsunamigenic potential. According to the distribution map of earthquakes epicenters and as well as to the map of the areas with active faults, were established nine seismic sources such as Central Dobrogea (S1), Shabla (S2), Istanbul (S3), North Anatolian Fault (S4), Georgia (S5), Novorossjsk (S6), Crimea (S7), West Black Sea (S8) and Mid Black Sea (S9). The maximum possible magnitude of the seismic source was made on seismotectonic and geological database, concerning international practice and IAEA recommendation or applying empirical formulas of Wells and Coopersmith. From the seismological point of view, the types of faults (earthquakes types) which are responsible for a tsunami are the thrust fault (associated with subduction zones), normal/inverse faults, and less strike-slip fault, if the oblique-slip and deep slip components are a predominant, magnitude higher than 6.5 and depth, a crustal one, less than 40 km depth. The major contribution to the total seismic hazard in the western part of the Black Sea is given by the Shabla crustal source with a maximum epicentral intensity equal to VIII ½

Authors:
Craiu M.G., Craiu A., Mihai M., Mărmureanu A.

Abstract:
The seismicity of Romania is significantly affected by earthquakes produced by the Vrancea seismic source with intermediate depth events (3 shocks/century with magnitude Mw greater than 7.0). The seismic activity on the Romanian territory consists of both shallow and intermediate-depth earthquakes. The crustal seismicity is moderate and more scattered in comparison with the intermediate-depth one. The recent upgrade of the seismic network in Romania with high dynamic range velocity sensors (150 real time seismic stations equipped with broadband and short period sensors) allows recording of moderate to large magnitude earthquakes at very close epicentral distances (less than 10-20 km). The purpose of this work consists mainly in the estimation of moment magnitude Mw along with other source parameters (M0, f0, and the focal mechanisms) using the velocity network of the NIEP. A stable and automatic method was developed by [1] and has been implemented in the real time data acquisition and processing system (ANTELOPE) [2] to estimate in real time the seismic moment, the moment magnitude and the corner frequency of events recorded by the velocity sensors, using Andrews (1986) method applied to S waves [3]. The main goals are the independent estimation of seismic moment and the common characterization for all events recorded by the velocity network. In this study were analyzed 329 seismic events recorded in Romania with 1.7?ML?6.0, during 2004-2021.

Authors:
Mihai M.,Craiu M.G., Craiu A., Mărmureanu A.

Abstract:
Romanian seismicity, is characterized by a moderate rate of tectonic origin earthquakes, with an increase in density and higher magnitudes, within the Vrancea region, located at the South-Eastern Carpathians bend, at the conjunction of three major tectonic units: East European Plate, Intra-Alpine Plate and Moesian Plate. First-motion focal mechanism solutions are a good proxy for the initial rupture and they provide important additional information on the source mechanism. The data compiled in the present paper provides earthquake parameters for individual events of interest to contribute, as a valuable source of information, for further studies as seismotectonic investigations and stress distribution maps. We calculated the focal mechanisms using as a reference the phase pickings reported in the Romplus Catalogue, for intermediate depth earthquakes recorded in Vrancea region during 2015 – 2021. To determine fault planes solutions was implemented the FPFIT code [1] (code that generates parameters: strike, dip, rake, etc.) in ANTELOPE 5.6, software developed by Kinemetrics. This code (FPL) uses the classic criteria to determine the focal mechanisms, namely P wave polarities, systematic tests of all possible fault plane solutions, so will validate only those solutions who met the required criteria. Estimating the near-real-time fault planes solutions using dedicated programs, a few minutes after the event occurrence is done by generating locations of the seismic events with magnitude ML?3.5 for seismic events occurred at intermediate depths (H>60 km).

Authors:
Craiu A., Aldea A., Rădulescu V., Drăgășanu C., Mihnea I.

Abstract:
The field of Earth Sciences has always been at the border between fundamental and applied research. If the fundamental part remains the complexity and unpredictability of research on Earth and natural phenomena, development and applied innovation are anchored in society and give a norm of the impact of research for society. The SETTING project aims to coordinate a distributed infrastructure that owns and can provide data, products and services (DPS) relevant to the field of Earth Sciences, to a wide and diverse community of users, through a scalable IT platform. In order to have a clear picture of this vast field of geosciences, the platform will contain and make accessible comprehensive information (e.g. formats, applied standards, their volume, regime and availability) about the main infrastructures and institutions involved in monitoring and research in this field. They will be organized in a database and access (query, selective search, etc.) will be done through specialized tools (web interfaces). This project is built on monitoring infrastructures, data and research available at national level, developed through own financing or from the budget, as well as through the implementation of national projects and /or financed by the EU framework. Furthermore, the project aims to create a framework for governance and management of data and services in the field of Earth Sciences, to ensure their interoperability and integration into a distributed national platform, in order to facilitate innovation and the development of new services based on inter and multidisciplinary data. Also, the IT platform will help researchers, practitioners and administration to critically evaluate the quantity and quality of available data, to identify needs and propose improvement solutions. Last but not least, the IT platform will allow the development of consortiums aiming to solve specific challenges and/or to perform research at national or international level.

Authors:
Craiu A., Ionescu C., Drăgan M.A.

Abstract:
The European Plate Observing System (EPOS), is a multidisciplinary, distributed research infrastructure that facilitates the integrated use of data, data products, and facilities from the solid Earth science community in Europe. The EPOS pan-European dimension is corroborated by 25 countries, 5 international organizations, 149 national research organizations and 256 research infrastructures involved in the data and service provision. The legal and governance framework designed during the Preparatory Phase and developed during the Implementation Phase has now to be consolidated and formally established to enable the European Plate Observing System – European Research Infrastructure Consortium (EPOS ERIC) governance of the EPOS Delivery Framework. Romania's involvement in EPOS is in line with the national strategy for consolidating, integrating and insuring of an adequate use for research infrastructures, and in full compliance with the main requests for technological and scientific research. Romania, represented by the Romanian National Institute for Research and Development for Earth Physics (INCDFP), was involved in the EPOS project from the very beginning and participated in all phases of the project (Preparation Phase, Implementation Phase and Sustainability Phase) along with other universities and European research institutions. To accomplish and develop a distributed infrastructure in the field of Earth sciences at the national level, a Romanian consortium was established between 7 research institutions and universities (National Institute for Research and Development for Earth Physics - INCDFP, National Institute for Research and Development on Marine Geology and Geo-ecology – GeoEcoMar, Romanian Geological Institute – IGR, University of Bucharest - UB - Faculty of Geology and Geophysics/ Faculty of Physics, INCD in Construction, Urbanism and Sustainable Territorial Development - URBAN-INCERC, Technical University of Civil Engineering Bucharest - UTCB, Romanian Academy, Institute of Geodynamics "Sabba S. Stefanescu"), in 2014. The new infrastructure EPOS-RO will ensure the possibility for inter and multi-disciplinary research that will use seismological, geophysics and geodesical data combined with geological and satellite data, resulting a simple analysis for natural hazards and precise estimations of the natural resources potential and a better understanding of the dependencies between different components of the natural environment.

Authors:
Kovacs I.J., Liptai N., Koptev A., Cloetingh S.A.P.L., Lange T.P., Matenco L., Szakacs A., Radulian M., Berkesi M., Patko L., Molnar G., Novak A., Wesztergom V., Szabo C., Fancisk T.

Abstract:
Apart from the lithosphere-asthenosphere boundary (LAB), mid-lithospheric discontinuities (MLDs) in thick and old continental lithospheres appear to play an important role in global plate tectonics. Initiation of intracontinental subduction, delamination of the lower continental lithospheric mantle and removal of cratonic roots are likely to occur along MLDs. Here we introduce the 'pargasosphere' hypothesis which could account for the origin of both boundaries. The observation that pargasitic amphibole is stable even at very low bulk 'water' concentration (-a few hundreds ppm wt.) implies that the solidus of the shallow upper mantle (< 3 GPa) is usually the pargasite dehydration solidus at -1100 degrees C. In young continental and oceanic lithosphere (< 70 Ma) this solidus defines the LAB. The LAB separates the deeper, partial melt bearing asthenosphere from the shallower melt barren lithosphere, explaining their contrasting rheology. In old continents pargasite breaks down at the sub-solidus pargasite dehydration boundary at similar to 3 GPa and liberates 'water'-rich fluids. This latter process may be responsible for the formation of MLDs. The occurrence of partial melts or fluids beyond the pargasite stability field can explain commonly observed geophysical anomalies associated with the LAB and MLDs. We present forward modelled variations of shear wave velocity and resistivity at the LAB and MLDs for idealised lithospheric columns. These columns are constructed based on the 'pargasosphere' hypothesis and geotherms corresponding to continental lithospheres with various tectono-thermal ages. The 'pargasosphere' hypothesis offers a number of other empirically testable implications. For instance, cooling asthenosphere beneath young extensional continental and oceanic lithosphere settings can be the source of surface CO2 emanations even at locations distant from areas with active volcanoes. The Vrancea zone (Eastern Europe) appears to be a suitable site for testing the 'pargasosphere' hypothesis for elucidating the origin of intermediate-depth earthquakes (70-300 km) and to explain the delamination of the lower continental lithospheric mantle.

Authors:
Petrescu L., Borleanu F., Radulian M., Ismail-Zadeh A., Matenco L.

Abstract:
Earthquake nests are anomalous clusters of seismicity located far from active collisional systems in intraplate, locked suture zones, or the deep part of relic subducted slabs, challenging classic earthquake generation mechanism theories. The Vrancea Seismic Zone in Romania is such an upper-mantle seismic nest located in the SE Carpathians, releasing the largest strain in continental Europe. To better understand earthquake generation and the relationship with lithospheric deformation, we estimate earthquake source parameters in Vrancea and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. In the crustal domain, maximum horizontal stress is in agreement with surface fault kinematics and GPS-derived S-SE trending horizontal plate velocities relative to Eurasia, implying that tectonic stress is vertically coherent on a crustal scale. The stress regime changes from transpression beneath the orogen to transtension towards the foreland where movement is accommodated along major crustal faults, and tension further away from the epicentre, in the Moesian Platform and the North Dobrogea Orogen. Inside the seismogenic body vertical tension and an overall compressive regime dominates, implying that vertical elongation may be the driving mechanism for brittle failure and that stress is transmitted along the sinking slab to the surface. However, the retrieved stress ratios are low: similar to 0.2 for mantle earthquakes Mw>4 and similar to 0.4 for Mw<4, challenging the brittle failure assumption. Increased pore fluid pressure has been shown to lower stress ratios, implying that dehydration embrittlement may contribute to generating intermediate-depth seismicity in the Vrancea slab. Comparisons with seismic tomography and anisotropy studies show excellent correlations between maximum horizontal stress directions, possible slab strike orientation, and seismic anisotropy, especially below similar to 130 km depth, suggesting ambient mantle flow may also promote in-slab stress build-up and seismic potential.

Authors:
Țigănescu A., Craifăleanu I.G., Bălan S.F.

Abstract:
The post-earthquake evaluation of structural integrity is a critical point to be addressed in case of emergency situations triggered by the occurrence of seismic events. A valuable method that can provide important indices to experts performing this operation is the monitoring of structures with seismic sensors that record how the structure responds to earthquake ground motion. In the case of permanent monitoring systems, reliable information can be obtained by comparing the data recorded before, during and after the earthquake, and checking if any abnormal vibrations of the structure or dynamic parameter changes have occurred. The presented study analysed comparatively, for an 11-story reinforced concrete building, vibration data recorded before, during and after the October 28th, 2018 earthquake (MW = 5.5). Continuously recorded data was used to determine the hourly values of the fundamental frequency of the building. The short-term behaviour (72 hours) was assessed, highlighting the modal parameters variation during, before and after the earthquake. In addition, an analysis of the data recorded one and a half hours before the earthquake and one and a half hours after the earthquake provided useful information on the evolution of the building state and on how this "recovered" after the earthquake.

Authors:
Grecu B., Borleanu F., Țigănescu A., Poiată N., Dinescu R., Tătaru D.

Abstract:
After the World Health Organization declared COVID-19 a pandemic in March 2020, Romania followed the example of many other countries and imposed a series of restrictive measures, including restricting people's mobility and closing social, cultural, and industrial activities to prevent the spread of the disease. In this study, we analyze continuous vertical component recordings from the stations of the Romanian Seismic Network - one of the largest networks in Europe, consisting of 148 stations - to explore the seismic noise variation associated with the reduced human mobility and activity due to the Romanian measures against COVID-19 in detail. We focused our investigation on four frequency bands - 2-8, 4-14, 15-25 and 25-40 Hz - and found that the largest reductions in seismic noise associated with the lockdown correspond to the high-frequency range of 15-40 Hz. We found that all the stations with large reductions in seismic noise (> similar to 40 %) are located inside and near schools or in buildings, indicating that at these frequencies the drop is related to the drastic reduction of human activity in these edifices. In the lower-frequency range (2-8 and 4-14 Hz) the variability of the noise reduction among the stations is lower than in the high-frequency range, corresponding to about 35 % on average. This drop is due to reduced traffic during the lockdown, as most of the stations showing such changes in seismic noise in these bands are located within cities and near main or side streets. In addition to the noise reduction observed at stations located in populated areas, we also found seismic noise lockdown-related changes at several stations located far from urban areas, with movement of people in the vicinity of the station explaining the noise reductions.

Authors:
Toader V.E., Nicolae V., Moldovan I.A., Ionescu C., Mărmureanu A.

Abstract:
This study analyzes the possibility to use geophysical and geochemical parameters in an OEF (Operational Earthquake Forecasting) application correlated with short-term changes in seismicity rates using a magnitude-frequency relationship. Tectonic stress over the limits of rock elasticity generates earthquakes, but it is possible that the emission of gases increases as a result of the breaking process. The question is how reliable is the emission of radon-222 and Carbon Dioxide (CO2), with effects on air ionization and aerosol concentration, in an OEF application? The first step is to select the seismic area (in our study this is the Vrancea area characterized by deep earthquakes at the bend of the Carpathian Mountains), then determine the daily and seasonal evolution of the forecast parameters, their deviations from the normal level, the short-term changes in seismicity rates using a magnitude-frequency relationship and finally to correlate the data with recorded seismic events. The results of anomaly detection, effect evaluation and data analysis alert the beneficiaries specialized in emergency situations (Inspectorate for Emergency Situations, organizations involved in managing special events). Standard methods such as the standard deviation from the mean value, time gradient, cross correlation, and linear regression are customized for the geological specificity of the area under investigation. For detection we use the short-time-average through long-time-average trigger (STA/LTA) method on time-integral data and the daily-seasonal variation of parameters is correlated with atmospheric conditions to avoid false decisions. The probability and epistemic uncertainty of the gas emissions resulting from this study, in addition to other precursor factors such as air ionization, time between earthquakes, temperature in the borehole, telluric currents, and Gutenberg Richter "a-b" parameters, act as inputs into a logical decision tree, indicating the possibility of implementing an OEF application for the Vrancea area. This study is novel in its analysis of the Vrancea area and performs a seismic forecasting procedure in a new form compared to the known ones.

Authors:
Borleanu F., Petrescu L., Enescu B., Popa M., Radulian M.

Abstract:
The Trans-European Suture Zone (TESZ) is the most important and extensive continental suture in Europe, marking the edge of the East European Craton (EEC), from the North Sea to the Black Sea. It corresponds to significant changes in surface geology and deep crustal structure, evident in seismic, gravitational and magnetic studies. However, the TESZ disappears beneath the Eastern Carpathians accretionary nappes and Neotethys ophiolites, thrusted over the subducted EEC passive margin in Romania that may have experienced progressive southward break-off generating post-collisional volcanism and anomalous seismicity in the Vrancea region of the South-East Carpathians. To illuminate the missing TESZ section and investigate the change in crustal properties from the Precambrian EEC across the collisional orogen and the impact of related volcanism, we determined a 3D seismic model of P and S wave velocities of the Eastern Carpathians in Romania. With the advent of new permanent broadband and short-period seismic stations of the Romanian Seismic Network, we were able to lower the earthquake magnitude detection threshold to 0.5 M-L, largely expanding the earthquake database and create seismic images of the crust across the Carpathians. Using double-difference tomography and waveform cross correlation differential times, we relocated local crustal earthquakes between 2010 and 2017 and jointly inverted for the 3D P and S-wave velocity structure down to the Moho discontinuity. Our study provides the highest resolution 3D crustal seismic model of this area to date and emphasizes the manifestation of surface tectonic boundaries at lower crustal depths. The TESZ is highlighted at mid-to lower-crustal depths beneath the Carpathian nappes, east of the post-collisional volcanic belt, as a gently-dipping transition from high Vp in the eastern footwall, the dipping Precambrian basement, to low Vp beneath the Carpathian Orogen to the west and a downward decrease in Vp/Vs. In parts of the volcanic region, Vp/Vs ratios increase suggesting the presence of fluids, mafic material and partial melts that may have altered the seismic structure of the TESZ. Relocated hypocenters are vertically distributed in the velocity transition zone from low to high especially beneath the youngest volcanoes in the south, consistent with a hypothetically active magmatic plumbing system. In the northern segment, where volcanoes are older, relatively high velocities are estimated and seismicity tends to cluster in the top 10 km, likely connected to a recently reactivated fault system. Seismicity in the foreland of the East Carpathians aligns along the NW-SE trending major crustal faults and continues beneath the thrust belt, suggesting the East European Craton basement extends beneath the orogen as far as the volcanic belt.

Authors:
Mihai A., Moldovan I.A., Toader V.E., Radulian M.

Abstract:
This paper discusses the use of ground magnetometer data to seismogenic zones and presents the relationship between anomalous geomagnetic variations and the occurrence of the intermediate-depth earthquakes. The present paper highlights the geomagnetic anomalies recorded at Muntele Rosu Seismological Observatory (MLR), between 2008 and 2013. To distinguish the global magnetic variations from possible seismo-electromagnetic anomalies presented in a seismic area like Vrancea zone, the data recorded on MLR were analyzed comparatively with the data recorded by the Surlari National Geomagnetic Observatory (SUA) which is located outside the Vrancea zone (150 km South-Est to Vrancea zone). Also, the geomagnetic indices taken from NOAA/Space Weather Prediction Center were plotted in order to separate these global variations caused by solar-terrestrial interaction. To highlight the relation between the geomagnetic anomalies and seismic activity of Vrancea zone, daily energy release, and total energy release calculations for each anomaly were performed.

Authors:
Plăcintă A.O., Borleanu F., Popescu E., Radulian M., Munteanu I.

Abstract:
Romanian seismicity is mainly confined to the Eastern Carpathians Arc bend (ECAB), where strong subcrustal earthquakes (magnitude up to 7.9) are generated in a narrow lithospheric body descending into the mantle. The seismic activity in the overlying crust is spread over a larger area, located mostly toward the outer side of the ECAB. It is significantly smaller than subcrustal seismicity, raising controversies about possible upper mantle-crust coupling. A significant earthquake sequence took place in the foreland of the ECAB triggered on 22 November 2014 by a mainshock of magnitude 5.7 (the greatest instrumentally recorded earthquake in this region) located in the lower crust. The mainshock triggered a significant increase in the number of small-magnitude events spread over an unusually large area in the ECAB. The paper's goal is to compute the source parameters of the earthquakes that occurred during the aforementioned sequence, by empirical application of Green's function and spectral ratio techniques. Fault plane solutions are determined using multiple methods and seismicity evolution at regional scale is investigated. Our results highlight a still active deformation regime at the edge of the EE Craton, while the source parameters reveal a complex fracture of the mainshock and a very high-stress drop.

Authors:
Manea E.F., Coman A., Cioflan C.O.

Abstract:
In this study, the predominant frequency of resonance was identified, interpreted and mapped along the National Seismic Networks of Romania, Republic of Bulgaria and Republic of Moldova, for the November 22, 2014, M-L = 5.7 crustal event generated at 40 km depth in the Vrancea seismogenic area. The horizontal-to-vertical spectral ratio technique was applied on the three-component single station measurements to investigate the local variability at each site. The observed predominant peaks are matching the fundamental frequency of resonance at some sites located on a superficial sedimentary cover and reach higher frequencies for the ones on deep sedimentary basins.

Authors:
Apostol B.F., Cune L.C.

Abstract:
The entropy of earthquakes is derived by using the Gutenberg-Richter statistical distributions. Both canonical and microcanonical earthquake distributions are given, and Einstein's fluctuation formula is deduced for earthquakes. The seismic activity of Vrancea in the period 1980-2019 is analyzed, for earthquakes with magnitude greater than two, and the results are compared with the theoretical results. It is shown that the parameter of the magnitude distribution exhibits a tendency of increasing with time, due to the accumulation of small-magnitude earthquakes, interrupted from time to time by ruptures towards smaller values, caused by earthquakes with greater magnitudes. These variations do not obey the normal distribution of the fluctuations. The (small) time variations of the distribution parameter provide a measure of the departure of the seismic activity from an equilibrium process. For Vrancea, these deviations are very small (up to 1% per year).

Authors:
Diaconescu M., Ghiță C., Moldovan I.A., Oros E., Constantinescu E.G., Marius M.

Abstract:
The main target of this paper is to established a correlation between the seismicity of the Western part of Southern Carpathians (Romania) and the active tectonic (faults systems) of the area, the second target is to create a specific database of the faults (ROmanian DAtabase of SEismogenic Faults-RODASEF) in SHARE manner, for seismic hazard assessment process. In the studied area, we highlit the main faults form Hateg Basin, Moldova Noua-Oravita Basin, Caransebes-Orsova basin (Teregova) and Orsova-Mehadia-Cornereva faults system, which generate seismic sequences such as: 2002 Moldova Noua, 1991 Mehadia-Baile Herculane, 2014 Teregova, 2011 and 2013 Hateg seismic sequences.

Authors:
Ghiță C., Diaconescu M., Raicu R., Moldovan I.A., Roșu G.

Abstract:
The purpose of this study consists in the analyses of ETAS (Epidemic-Type Aftershock Sequence) parameters for the sequence recorded on November 22nd , 2014 in Marasesti area. The main shock of the sequence, a moderate-size earthquake with M-L = 5.7, at 40.9 km depth, is the largest crustal event instrumentally recorded at the bending of the Eastern Carpathians. The ETAS model parameters for the Marasesti area were estimated using the seismic events from the Romplus catalogue, between January 1, 2010 (00:00:00) and November 17, 2017 (00:00:00), with magnitude between 1.2 < M-w < 5.4 and depth 0.6 < h < 70 km. The estimated model is applied further on an independent data set recorded in the same area, for automatic identification of Marasesti sequences using the residual analysis techniques. The studied model encourages research for evaluation of the real-time probability earthquake occurrence and sustains the international initiatives such as the Operational Earthquake Forecast (OEF)

Authors:
Oros E., Plăcintă A.O., Moldovan I.A.

Abstract:
The paper presents a seismotectonic model of the Southern Carpathians obtained from the analysis of the seismicity-stress field-geology and tectonics relationship. The seismicity model is based on a revised earthquake catalogue. The distribution of b-values in the 3D space facilitated the identification of stressed areas and asperities with reactivation potential and their correlation with geological structures. The stress field has been modelled using the parameters of the stress tensor calculated by the formal inversion of the focal mechanisms. The reactivation potential of geological structures was estimated depending on the relationship between the fault planes geometry and the principal stress axes.

Authors:
Țigănescu A., Craifăleanu I.G., Bălan S.F.

Abstract:
The paper presents results from a study on monitoring the long-term variation of the dynamic characteristics of an 11-story reinforced concrete building located near Bucharest. Since the deployment, in December 2013, of a permanent monitoring system, 89 seismic events with a moment-magnitude (MW) larger than 3.8 were reported. Out of these, 80 were recorded properly by the seismic sensors and the data was used to extract the fundamental frequency and the damping ratio of the building for each event. The main method used to compute the dynamic parameters was the Random Decrement Technique. A dependency of the resulting fundamental frequencies on the maximum accelerations at the base and on top of the building was observed. Due to the structural peculiarities, the fundamental frequency of the building on the transverse direction was lower than the one on the longitudinal direction, this being reflected also by the experimental results. The maximum drop in the fundamental frequency was reported for the MW=5.5 October 28th, 2018 seismic event. By performing this type of analyses, the dynamic parameters of buildings can be tracked over long periods of time and their variation under seismic excitation can be assessed, allowing rapid detection of structural health alterations.

Authors:
Oros E., Plăcintă A.O., Moldovan I.A.

Abstract:
We present the study of the earthquakes sequence from 25 June to 6 July 2020 occurred in the western South Carpathians. The main shock had I-o = V degrees MSK, M-w = 4.1, occurred at h = 16 km, was preceded by a foreshock (M-w = 3.2) and has 16 after-shocks (M-w = 1.6-4.1) concentrated in the depth range 14-21 km. The focal mechanisms are characterized by strike-slip faults and P axes oriented N76 degrees E. The causative fault is dextral strike-slip oriented NE-SW, known as Cerna- Jiu Fault. The macroseismic data partially match the intensities attenuation and conversion acceleration-intensity relationships.

Authors:
Constantin A.P., Moldovan I.A., Partheniu R., Grecu B., Ionescu C.

Abstract:
The goal of this paper is to develop a new empirical relationship between observed macroseismic intensity and strong ground motion parameters such as peak ground acceleration (PGA) and velocity (PGV) for the Vrancea subcrustal earthquakes. The recent subcrustal earthquakes provide valuable data to examine these relationships for Vrancea seismogenic region. This region is one of the most active seismic zones in Europe and it is well-known for the strong subcrustal earthquakes. We examine the correlation between the strong ground-motion records and the observed intensities for major and moderate earthquakes with Mw >= 5.4 and epicentral intensity in the range VI to IX MSK degrees that occurred in Vrancea zone in the period 1977-2009. The empirical relationships between maximum intensity and ground parameters obtained and published by various authors have shown that these parameters do not always show a one-to-one correspondence, and the errors associated with the intensity estimation from PGA/PGV are sometimes +/-2 MSK degree. In the present study, the relation between macroseismic intensity and PGA/PGV will be given both as a mathematical equation, but also as corresponding ground motion intervals. Because of the intensity data spreading and errors related to mathematical approximations, it is necessary to systematically monitor not only the acceleration and velocity but also all the other ground motion parameters. The mathematical relation between these parameters might be used for the rapid assessment of ground shaking severity and potential damages in the areas affected by the Vrancea earthquakes.

Authors:
Poiată N., Vilotte J.P., Shapiro N.M., Supino M., Obara K.

Abstract:
We derive an extensive catalog of low-frequency earthquakes (LFEs) in western and central Shikoku applying an automatic, coherency-based detection and location method to 4-year long continuous data from selected seismic stations. Our catalog is the first LFE catalog in this area that does not rely on a priory templates and results from a homogeneous data processing scheme. It allows investigating in detail main characteristics of LFE activity in space and time. We observe clear heterogeneity of the LFE space distribution in the along-strike direction of the subducting Philippine Sea plate corresponding to segments with different sizes, some of which are highly productive in LFE generation. More detailed statistical and correlation-based analysis of LFE occurrence patterns allows quantification of the along-strike segmentation and examination of the migration and event interaction during the LFE sequences and inter-sequence periods. The analysis indicates that a strong interaction exists among LFE sources during slow slip events, but it otherwise varies significantly among the along-strike segments. We suggest that the observed segmentation of LFE activity is related to static heterogeneity, such as structural property variations along the subduction interface, or dynamic heterogeneity, corresponding to memory-dependent stress variations or possible fluid transients. We also confirm that regions with the highest LFE productivity correspond to spots of tectonic tremor triggered by teleseismic earthquakes' surface waves supporting a localized fluid-rich environment with possible fluid transients. Our results illustrate how high-resolution LFE catalog can contribute to the characterization and quantification of slow earthquake processes through detailed statistical analysis of their activity.

Authors:
Coman A., Manea E.F., Radulian M.

Abstract:
In this study, we investigate how the recorded seismic ground motion is influenced by the local/regional geological structure for sites located in the centre and western Romania. The Horizontal-to-Vertical Spectral Ratio (HVSR) technique was applied for 3.1–5.7 Mw events, to extract characteristics of the seismic wavefield and to evaluate the predominant frequency of resonance (fpred). The amplitudes of the HVSR curves computed for the events located along the Carpathian arc are strongly reduced by back-arc attenuation while no effects were observed for the others. The fpred matches relatively well the fundamental frequency at sites deployed on a superficial layer of sediments while a migration to higher frequencies were observed for complex sedimentary structures.

Authors:
Nistor S., Suba N.S., El-Mowafi A., Apollo M., Malkin Z., Năstase E.I., Kudrys J., Maciuk K.

Abstract:
The seasonal signal determined by the Global Navigation Satellite System (GNSS), which is captured in the coordinate time series, exhibits annual and semi-annual periods. This signal is frequently modelled by two periodic signals with constant amplitude and phase-lag. The purpose of this study is to explore the implication of different types of geophysical events on the seasonal signal in three stages—in the time span that contains the geophysical events, before and after the geophysical event, but also the stationarity phenomena, which is analysed on approximately 200 reference stations from the EPN network since 1995. The novelty of the article is demonstrated by correlating three different types of geophysical events, such as earthquakes with a magnitude greater than 6◦ on the Richter scale, landslides, and volcanic activity, and analysing the variation in amplitude of the seasonal signal. The geophysical events situated within a radius of 30 km from the epicentre showed a higher seasonal value than when the timespan did not contain a geophysical event. The presence of flicker and random walk noise was computed using overlapping Hadamard variance (OHVAR) and the non-stationary behaviour of the time series of the CORS coordinates in the time frequency analysis was done using continuous wavelet transform (CWT).

Authors:
Toader V.E., Mihai A., Moldovan I.A., Ionescu C., Mărmureanu A., Lingvay I.

Abstract:
Large‐scale radon monitoring is carried out due to the fact that it is directly responsible for public health. European Directive 2013/59/EURATOM has been transposed into the legislation of several countries and provides for the need for long‐term monitoring of radon in homes and workplaces by setting the average annual reference level at 300 Bq/m3. At the same time, radon is a precursor factor, its emission being correlated with seismic and volcanic activity. In this case, the protection of the population is ensured by a forecast similar to a meteorological one. The NIEP (Na-tional Institute for Earth Physics) is developing a multidisciplinary real‐time monitoring network in the most dangerous seismic area in Romania, Vrancea. This is located at the bend of the Carpathian Mountains and is characterized by deep earthquakes (over 80 km), with destructive effects over large distances. Implementing a multidisciplinary monitoring network that includes radon, in-volves finding the locations and equipment that will give the best results. There is no generic solution for achieving this, because the geological structure depends on the monitoring area, and in most cases the equipment does not offer the ability to transmit data in real time. The positioning of the monitoring stations was based on fault maps of the Vrancea area. Depending on the results, some of the locations were changed in pursuit of a correlation with zonal seismicity. Through re-peated tests, we established the optimal sampling rate for minimizing errors, maintaining measurement accuracy, and ensuring the detection of anomalies in real time. The radon222 Rn was determined by the number of counts and ROI1 (region of interest) values, depending on the particulari-ties of the equipment. Finally, we managed to establish a real‐time radon monitoring network which transmits data to geophysical platforms and makes correlations with the seismicity in the Vrancea area. The equipment, designed to store data for long periods of time then manually download it with manufacturers’ applications, now works in real time, after we implemented software designed specifically for this purpose.

Authors:
Manea E.F., Cioflan C.O., Danciu L.

Abstract:
A newly compiled high-quality ground-shaking dataset of 207 intermediate-depth earthquakes recorded in the Vrancea region of the south-eastern Carpathian mountains in Romania was used to develop region-specific empirical predictive equations for various intensity measures: peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral acceleration up to 10 s. Besides common predictor variables (e.g. moment magnitude, depth, hypocentral distance, and site conditions), additional distance scaling parameters were added to describe the specific attenuation pattern observed at the stations located not only on the back and fore but also along the Carpathian arc. In this model, we introduce a proxy measure for the site as the fundamental frequency of resonance to characterize the site response at each recording seismic station beside the soil classes. To additionally reduce the site-to-site variability, a non-ergodic methodology was considered, resulting in a lower standard deviation of about 25%. Statistical evaluation of the newly proposed ground-motion models indicates robust performance compared to regional observations. The model shows significant improvements in describing the spatial variability (at different spectral ordinates), particularly for the fore-arc area of the Carpathians where a deep sedimentary basin is located. Furthermore, the model presented herein improves estimates of ground shaking at longer spectral ordinates (>1 s) in agreement with the observations. The proposed ground-motion models are valid for hypocentral distances less than 500 km, depths over 70 km and within the moment magnitude range of 4.0–7.4.

Authors:
Constantin A.P., Moldovan I.A., Partheniu R., Ionescu C.

Abstract:
The correlations between macroseismic intensity (MI) and strong ground motion parameters such as Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) for the Vrancea subcrustal earthquakes are compared. The recent Romanian earthquakes, especially Vrancea earthquakes provide valuable data to examine the correlation relationships between these parameters for the entire territory of Romania. The goal of this study is to develop a new empirical relationships between the strong ground-motion records and the observed intensities for major and moderate earthquakes with Mw ≥ 5.4 and epicentral intensity in the range VI to IX MSK degrees that occurred in the period 1977–2009. For each instrumental record we assigned a macroseismic intensity based on the proximity of the site where reported value are available (no more than 3 km distance around the station). The obtained relations between macroseismic intensity and PGA/PGV will be given both as a mathematical equations, but also as corresponding ground motion intervals. The most prominent results available in the literature have shown that macroseismic intensity and ground parameters do not always show a one-to-one correspondence, and the errors associated with the intensity estimation from PGA/PGV are sometimes +/–2 MSK degree. These relations can be used as near real-time response regarding ground shaking severity, and potential damages in the areas affected by the Vrancea earthquakes.

Authors:
Nistor S., Suba N.S., Maciuk K., Kudrys J., Năstase E.I., Muntean A.

Abstract:
This study evaluates the EUREF Permanent Network (EPN) station position time series of approximately 200 GNSS stations subject to the Repro 2 reprocessing campaign in order to characterize the dominant types of noise and amplitude and their impact on estimated velocity values and associated uncertainties. The visual inspection on how different noise model represents the analysed data was done using the power spectral density of the residuals and the estimated noise model and it is coherent with the calculated Allan deviation (ADEV)-white and flicker noise. The velocities resulted from the dominant noise model are compared to the velocity obtained by using the Median Interannual Difference Adjusted for Skewness (MIDAS). The results show that only 3 stations present a dominant random walk noise model compared to flicker and powerlaw noise model for the horizontal and vertical components. We concluded that the velocities for the horizontal and vertical component show similar values in the case of MIDAS and maximum likelihood estimation (MLE), but we also found that the associated uncertainties from MIDAS are higher compared to the uncertainties from MLE. Additionally, we concluded that there is a spatial correlation in noise amplitude, and also regarding the differences in velocity uncertainties for the Up component.

Authors:
Šindelářová T., De Carlo M., Czanik C., Ghica D., Kozubek M., Podolská K., J.Baše, Chum J., Mitterbauer U.,

Abstract:
The Central and Eastern European Infrasound Network (CEEIN) detects significant irregularities in microbarom arrivals between 15 and October 18, 2017. The processes driving the irregular microbarom arrivals are searched in the microbarom source region in the North Atlantic and in the stratospheric waveguide. Generation of microbaroms is simulated using ocean WAVEWATCHIII wave-action model and an updated source theory which combines the effects of both finite depth ocean and source directivity. Signal propagation in a uniform range independent atmosphere is considered. In the studied time interval, a dominant moving microbarom source occurs at the tail of the post-tropical storm Ophelia. The storm Ophelia provides an opportunity to study the development of an intense microbarom source on the open ocean and particularly in coastal waters. Discrepancies between observations and modelling results are identified and discussed. This study shows that the state-of-the-art wave-action models are underestimated in coastal areas during storms which can pose a problem for civil security in coastal areas. The capability of the CEEIN stations to monitor microbaroms is proved. Measurement biases and uncertainties associated with the configurations of the CEEIN stations and current limitations of the processing method are discussed and improvements are suggested.

Authors:
Namjesnik D., Kinscher J., Gunzburger Y., Poiată N., Dominique P., Bernard P., Contrucci I.

Abstract:
In post-mining regions with seismic hazard, timely decision making for risk management faces the challenge of quick and reliable detection and location of seismic events. As a response to the increasing density of monitoring stations, generating large volumes of seismic data, automatic, full waveform-based methods have been developed in recent years in global seismology. Such methods often cannot be directly applied to post-mining monitoring with a limited station coverage, as it is the case when temporarily networks are installed as an emergency response. In this paper we propose a new methodology that bridges this gap and enables the application of a full waveform, backprojection based method (BackTrackBB) to data of sparse network. The methodology was successfully tested on an abandoned and flooded underground coalmine in South-eastern France. Steps preceding BackTrackBB application were implemented in order to remove the coherent noise that otherwise results in numerous false detections. First results indicate that seismic activity in the study area is controlled by water level variation within former room-and-pillar mine works and fault segments (re)activation below them.

Authors:
Eeken T., Goes S., Petrescu L., Altoe I.

Abstract:
The origin of 3-D seismic heterogeneity in Precambrian lithosphere has been enigmatic, because temperature variations in old stable shields are expected to be small and seismic sensitivity to major-element compositional variations is limited. Previous studies indicate that metasomatic alteration may significantly affect average 1-D structure below shields. Here, we perform a grid search for 3-D thermochemical structure, including variations in alteration, to model published Rayleigh wave phase velocities between 20 and 160 s for the eastern part of the Archean Superior and Canadian Proterozoic Grenville Provinces. We find that, consistent with constraints from surface heat flow and xenoliths, the lithosphere is coolest (Moho heat flow 12–17 mW/m2) and the thermal boundary layer thickest (>250 km) in the northeastern Superior and warmest in the southeastern Grenville (Moho heat flow 20–25 mW/m2, thermal boundary thickness 160–200 km). Compositionally, the phase velocities for most of the Superior within our study region require little alteration, but in a few regions, fast velocities need to overlie slower velocities. These can be modeled with an eclogite layer in the midlithosphere, consistent with active seismic and xenolith evidence for remnants of subducted Archean crust. The phase velocities from the Grenville Province require significant metasomatic modification to explain the relatively low velocities of the shallow lithosphere, and the required intensity of alteration is highest in parts of the Grenville associated with arc accretion. Thus, the composition of the northeastern Canadian Shield appears to reflect different stages and styles of craton assembly.

Authors:
B. F. Apostol, S. F. Balan, A. Tiganescu

Abstract:
The seismic response and local seismic effects are analysed in terms of spectral accelerations, peak ground acceleration (PGA) and site’s oscillation periods for city of Bucharest. By means of these parameters we may characterize the seismic hazard generated over the city area by Vrancea intermediate-depth seismic source. A data set consisting of the available seismic recordings is used for the last strong Vrancea earthquakes (Mw > 6.4). Also, the geological description and interpretation of data contained in detailed geological maps is employed as the main and most basic information necessary to perform such an investigation. The existence of down-hole data complements the geological information. The necessity of defining a dominant period-value range corresponding to seismic movements for each site is highlighted, by comparing some terrain characteristics induced by strong events (acceleration, response spectra, oscillating period of the superficial soil deposit) and their changes related to the magnitude of the earthquake. Despite the fact that seismic effects may not be characterized entirely by critical values in the range of the nonlinear effects, the particular geological features of the Romanian capital Bucharest may induce various amplifications, as a response to major earthquakes. These data about soil deposits behaviour could be used as input data for seismic risk mitigation. They provide an important contribution, in a very effective way, to getting solutions toward a safer seismic design.

Authors:
Țigănescu A., Grecu B., Craifăleanu I.G.

Abstract:

Authors:
Plăcintă A.O, Popescu E., Moldovan I.A., Radulian M., Mihai A

Abstract:
The seismic hazard studies of the last 30 years have been largely carried out taking into account the needs of the construction engineers, by linking the specific quantities of soil movement with the physical parameters determined instrumentally, namely, with the maximum values of soil acceleration. At present, interest in the results of hazard studies has increased and has extended to other areas such as insurance or design companies, environmental protection, etc. A fundamental element in the estimation of seismic hazard is the variation of the amplitude of the movement of the soil according to the distance, magnitude and local conditions. To understand and prevent the effects of the strong Vrancea earthquakes in the dam sites located in the South West of Romania, we study the seismic waves attenuation relations using the accelerations recorded by the national network of K2 accelerometers, following the moderate Vrancea intermediate earthquakes. The study area includes the largest agglomeration of dams in Romania, with almost 100 dams out of the 250 large dams. One of the most important specific requirements towards dams' safety is the seismic risk and hazard assessment and the computation of attenuation relationships is one of the most important steps of the work. The main objective of the present work is the evaluation of the specific attenuation relationships of the seismic wave propagating from Vrancea subcrustal focus toward south-west, with direct application for the dams situated in the area.

Authors:
N. D. Mateciuc, A. Bălă

Abstract:
The studies for Recent Crustal Movements by the aid of space geodesy techniques are integrated into the researches on the Earth’s crust dynamics, as a reflection of the complex geodynamic phenomena that occur in the crust and in the subcrustal lithosphere. In addition to the fundamental nature, the research in this field presents a practical characteristic, competing alongside geology and geophysics to the shaping of new energy sources or solid mineral substances, to the determination of the soil stability degree in inhabited areas or in those in which large industrial targets and utilities are intended to be placed in. The knowledge of movements affecting the Earth’s upper crust, movements that precede, accompany or follow the earthquakes, is also a topical issue. The paper presents some of the most important research projects developed in Romania, which were based on the measurement data obtained exclusively by space geodesy methods. There are presented some of the most significant results achieved in the framework of each research project together with the limitations imposed by the used acquisition technology. In chronological order are mentioned first GPS measurements in Romania, started in 1994, in a network centered on the Dealul Piscului observatory, followed by Romania's involvement in a regional geodynamic project, CERGOP and finally a major international project, CRC461, also continued after 2003 with the continuous help of the University of Delft (Nederland), a project that led to the development of an extended network of GPS permanent stations in Romania, all in operating status and whose results are a valuable support for the geodynamic studies. There are made brief references to the first application of the Finite Element Method in a GPS subnet from the Vrancea extended network together with some of the most important obtained results. The strong earthquakes with their catastrophic consequences, which have taken place in recent years on a global scale, similar to that of 4 March 1977 in Romania, have fully demonstrated the need for the knowledge of these types of crust movements in order to contribute, together with other methods, to solve the very complex problem of the earthquake forecasting.

Authors:
Constantin, A. P.; Manea, E. F.; Moldovan, I. A.; Partheniu, R.

Abstract:
The aim of the present paper is to test intensity attenuation relationships for subcrustal earthquakes occurred in Vrancea (Romania) seismogenic zone in relation with some important dams situated in extra-Carpathian area. During centuries, the Romanian territory has been shaken by strong earthquakes, most of them being centered within Vrancea Zone, which is situated at the bending area of the South-Eastern Carpathians. Most of the zones from extra-Carpathian area are affected by the subcrustal seismic events, where many hydro-technical structures exist, being also exposed to earthquakes action. A detailed analysis of the intensity attenuation laws developed for subcrustal seismic sources was performed using the most recent and complete intensity datasets. We use an extended and combined intensity data including historical and modern, qualitative and quantitative data, i.e. a number of 11 earthquakes occurred during the period 1738-2009 with epicentral/maximum intensities ranging from VII-X MSK degrees, and magnitude Mw from 5.4 to 7.9. All the input data used for testing are resulted after the reevaluation and evaluation of the macroseismic effects produced by the seismic events included in the present study (8697 IDP). The selected attenuation laws were tested for different values of epicentral intensity and with reference to twelve and twenty four azimuthal directions. Besides the testing of the relationships, isoseismal maps based on the selected attenuation laws were accomplished, associated to the biggest possible earthquake (worst scenario) for the Vrancea subcrustal zone, also highlighting the calculated intensities in the selected dam sites. Brief description of the study and used methods. Brief description of the study and used methods.

Authors:
Ardeleanu L., Neagoe C., Ionescu C.

Abstract:
Empirical relationships between MSK macroseismic intensity and several engineering ground motion parameters are developed using the macroseismic and instrumental data available for five significant earthquakes (Mw magnitude 6 and above), which occurred during the past half-century in Vrancea region, Romania. The relations are suitable for the Carpathian bend zone and surroundings, and they are valid for intensity values between 5 and 8; in this range, the MSK intensity is basically defined by the level of structural damage. The capability of the selected ground motion parameters to predict the macroseismic intensity is evaluated by observing the standard deviations associated with the proposed regression models. Generally, the parameters which take into account the ground motion duration appear to be more stable predictors than the parameters based on the peak ground motion. The most reliable damage indicator appears to be the Arias intensity. The proposed regression relationships provide intensity predictions with uncertainty close to one-half unit; therefore, they are reliable tools for rapid loss estimation and emergency response coordination following a strong earthquake of Vrancea region. The derived equations represent also useful instruments for seismic risk assessment by methodologies based on macroseismic intensity, since in current practice the earthquake hazard and seismic impact are mainly given in terms of engineering ground motion parameters.

Authors:
Palgunadi K.H., Poiată N., Kinscher J., Bernard P., De Santis F., Contrucci I.

Abstract:
Recent studies have demonstrated the success of automatic full-waveform detection and location methods in analyzing and monitoring natural and induced seismicity. These approaches have been shown to provide a significant improvement in events detectability, increasing the significance of statistical analysis that permits to identify small changes of seismicity rates in space and time. Although currently nontrivial and by far nonstandard, application of such methods to seismic monitoring of active mines could significantly improve forecasting of potential destructive rockburst events. The main challenges of such applications are related to the presence of a wide range of seismic noise sources that have to do with mining activity and a high sampling rate of recorded data (several kHz), posing problems for real-time data transfer and processing. In this study, we propose an adapted full-waveform-based automatic method for the detection and location of microseismic events that makes use of continuous seismic records from an in-mine seismic network and can be adjusted to a near-real-time monitoring scheme. The method consists of two steps: (1) event extraction and amplitude ratio-based preliminary location and (2) event relocation using a coherency-based back-projection approach. The event extraction, based on multiband signal characterization implemented in the first step, allows us to overcome the challenge of high sampling rate data (8 kHz), reducing the overall volume of transferred data and providing an energy-based signal classification scheme. This allows us to remove a significant number of machinery noise sources. The technique is developed and tested on the case study of the Garpenberg mine (Sweden) monitored by a local seismic network that is maintained by Ineris. We demonstrate the improvement in event detection capacity by a factor of 50, compared with the standard triggered-based monitoring schemes. This increased number of detected microseismic events permits us to investigate the migration pattern of induced microseismicity that is generated in response to production blast.

Authors:
Oros E., Plăcintă A.O., Popa M., Diaconescu M.

Abstract:
The paper represents a multidisciplinary investigation of the relation between seismicity, active stress field and geological structure for the West of Romania. The study is based on revised and updated catalogues of earthquakes (3572 events) and focal mechanisms (89 solutions). The large spatio-temporal variations of the stress tensor parameters, b-value (b=0.74-0.81) and fractal dimensions of seismicity (D=1.05-2.34) highlight both clustering patterns along active fault systems and scattered epicentres within planes or volumes. A tectonic model with at least three blocks bordered by active faults is proposed controlling SHmax trend: it rotates clockwise in time and 3D space by up to 900 along with the changes of the stress regime from the compressional to extensional and activity migration between two major and complex fault systems. Low b-values characterize the regardless of the size of data source, but the smaller source/dataset, with or without aftershocks included, ensures a more realistic estimation of seismic hazard that is confirmed by seismic history (Tr_Mw5.5 = 76 years).

Authors:
Ghiță C., Diaconescu M., Moldovan I.A., Oros E., Constantinescu E.G.

Abstract:
In this paper, we have studied the seismic activity in relation with geology, and tectonics in order to highlight seismogenic processes recorded in Danubian area and Hateg-Strei Basin. The Danubian seismogene area presents a complex geological structure, being characterized by the following tectonic units: Median Dacides (Getic and Supra-Getic nappes), Marginal Dacides (Danubian Unit) and External Dacides (Severin nappe). The recent seismic activity in this area, starting from 1990 until present, is described by the seismic sequence from 2002, in the Moldova Noua area, in connection to Oravita-Moldova Noua fault and by the seismic sequence from 1991, in the Baile Herculane area, belonging to the Cerna-Jiu fault system. Also, the Teregova area is present with the seismic sequence from 2014 and another two smaller sequences. From a statistical point of view, the seismicity is mainly described by the b-value coefficients from the empirical relation between the frequencies and magnitudes. Determination of spatial and temporal variations of the b-value is thought to reflect the stress conditions in the crust.

Authors:
Năstase E. I., Muntean A., Nistor S., Grecu B., Tătaru D.

Abstract:
Nowadays, advances in GNSS receivers technology and computational algorithms such as 1 Hz acquisition rate (and even more, up to 50 Hz), that are commonly available, make us search worldwide for systems & algorithms that would make possible a real‐time estimation of waveforms and coseismic displacements. The present paper highlights the results obtained in recent years by looking at the Romanian GNSS data over 3 different study cases from another perspective, aims to elaborate on a number of issues and provide some directions for future work that involve nontraditional seismological sensors such as GPS and tiltmeters following the implementation of the new generation of tools into GNSS permanent reference network data processing, in help for a more accurate assessment of the Vrancea earthquakes impact.

Authors:
Oros E., Plăcintă A.O., Popa M., Diaconescu M.

Abstract:
The paper represents a multidisciplinary investigation of the relation between seismicity, active stress field and geological structure for the West of Romania. The study is based on revised and updated catalogues of earthquakes (3572 events) and focal mechanisms (89 solutions). The large spatio-temporal variations of the stress tensor parameters, b-value (b=0.74-0.81) and fractal dimensions of seismicity (D=1.05-2.34) highlight both clustering patterns along with active fault systems and scattered epicentres within planes or volumes. A tectonic model with at least three blocks bordered by active faults is proposed controlling SHmax trend: it rotates clockwise in time and 3D space by up to 90 degrees along with the changes of the stress regime from the compressional to extensional and activity migration between two major and complex fault systems. Low b-values characterize the regardless of the size of data source, but the smaller source/ dataset, with or without aftershocks included, ensures a more realistic estimation of seismic hazard that is confirmed by seismic history (Tr_Mw5.5 = 76 years).

Authors:
Ardeleanu, L., Neagoe, C., Ionescu, C.

Abstract:
Empirical relationships between MSK macroseismic intensity and several engineering ground motion parameters are developed using the macroseismic and instrumental data available for five significant earthquakes (Mw magnitude 6 and above), which occurred during the past half-century in Vrancea region, Romania. The relations are suitable for the Carpathian bend zone and surroundings, and they are valid for intensity values between 5 and 8; in this range, the MSK intensity is basically defined by the level of structural damage. The capability of the selected ground motion parameters to predict the macroseismic intensity is evaluated by observing the standard deviations associated with the proposed regression models. Generally, the parameters which take into account the ground motion duration appear to be more stable predictors than the parameters based on the peak ground motion. The most reliable damage indicator appears to be the Arias intensity. The proposed regression relationships provide intensity predictions with uncertainty close to one-half unit; therefore, they are reliable tools for rapid loss estimation and emergency response coordination following a strong earthquake of Vrancea region. The derived equations represent also useful instruments for seismic risk assessment by methodologies based on macroseismic intensity, since in current practice the earthquake hazard and seismic impact are mainly given in terms of engineering ground motion parameters.

Authors:
Metaxian J.P., Santoso A.B., Caudron C., Cholik N., Labonne C., Poiată N., Beauducel F., Monteiller V., Fahmi A.A., Rizal M.H., Nandaka I.G.M.A.

Abstract:
Phreatic activity of Merapi started after nearly 2 years of quiescence following the October–November 2010 eruption which was the largest in more than 100 years. A dozen eruptions identified by visual and/or seismic observations took place between August 2012 and April 2014. We present in this work the results of a detailed analysis of the April 20, 2014 phreatic eruption. We attempted to reconstruct the eruptive process, which lasted for over 30 min. To this end, we determined the wavefield composition by polarization analysis, located high-frequency earthquakes occurring in the initial part of the eruption process and then determined the seismic source migration of low-frequency part of the tremor-like signal [0.3–3 Hz] over time. Source depth of low-frequency signal was obtained by comparing the slowness vector calculated using 3 stations of the seismic antenna with a slowness vector model obtained by ray tracing in the structure, taking into account the topography and a 1D velocity model obtained by spatial auto-correlation analysis. The results allow to distinguish 3 different phases: 1) High-frequency transients interpreted as the result of a sudden decompression caused by the transition of the volcanic fluid to a gaseous phase that occurred approximately 1.5 km deep. This decompression process in the hydrothermal system generated a migration of the low-frequency seismic source from 900 m to 1800 m above sea level; 2) A second decompression process revealed by high-frequency micro-seismicity and associated to the migration of the low-frequency tremor source which is marked first by a descent phase, followed by a sharp ascent until reaching the surface. The evolution of the back-azimuth during the migration process indicates a slight inclination of the conduit, presumably in the orientation of the dome fracture, in the NW-SE direction. This direction is consistent with the alignment of regional tectonic structures and with the directivity of eruption deposits. 3) The seismic source then remains positioned at the altitude of the dome for over 10 min. This phase probably corresponds to the ash emission process. The average migration speed of the low-frequency seismic source from the starting eruptive process to ash emission is about 5 m/s.

Authors:
Petrescu L., Stuart G., Houseman G., Bastow I.

Abstract:
Since the Mesozoic, central and eastern European tectonics have been dominated by the closure of the Tethyan Ocean as the African and European plates collided. In the Miocene, the edge of the East European Craton and Moesian Platform were reworked in collision during the Carpathian orogeny and lithospheric extension formed the Pannonian Basin. To investigate the mantle deformation signatures associated with this complex collisional-extensional system, we carry out SKS splitting analysis at 123 broad-band seismic stations in the region. We compare our measurements with estimates of lithospheric thickness and recent seismic tomography models to test for correlation with mantle heterogeneities. Reviewing splitting delay times in light of xenolith measurements of anisotropy yields estimates of anisotropic layer thickness. Fast polarization directions are mostly NW–SE oriented across the seismically slow West Carpathians and Pannonian Basin and are independent of geological boundaries, absolute plate motion direction or an expected palaeo-slab roll-back path. Instead, they are systematically orthogonal to maximum stress directions, implying that the indenting Adria Plate, the leading deformational force in Central Europe, reset the upper-mantle mineral fabric in the past 5 Ma beneath the Pannonian Basin, overprinting the anisotropic signature of earlier tectonic events. Towards the east, fast polarization directions are perpendicular to steep gradients of lithospheric thickness and align along the edges of fast seismic anomalies beneath the Precambrian-aged Moesian Platform in the South Carpathians and the East European Craton, supporting the idea that craton roots exert a strong influence on the surrounding mantle flow. Within the Moesian Platform, SKS measurements become more variable with Fresnel zone arguments indicating a shallow fossil lithospheric source of anisotropy likely caused by older tectonic deformation frozen in the Precambrian. In the Southeast Carpathian corner, in the Vrancea Seismic Zone, a lithospheric fragment that sinks into the mantle is sandwiched between two slow anomalies, but smaller SKS delay times reveal weaker anisotropy occurs mainly to the NW side, consistent with asymmetric upwelling adjacent to a slab, slower mantle velocities and recent volcanism.

Authors:
Li L., Tan J.Q., Schwarz B., Stanek F., Poiata N., Shi P.D., Diekmann L., Eisner L., Gajewski D.

Abstract:
Source locations provide fundamental information on earthquakes and lay the foundation for seismic monitoring at all scales. Seismic source location as a classical inverse problem has experienced significant methodological progress during the past century. Unlike the conventional traveltime-based location methods that mainly utilize kinematic information, a new category of waveform-based methods, including partial waveform stacking, time reverse imaging, wavefront tomography, and full waveform inversion, adapted from migration or stacking techniques in exploration seismology has emerged. Waveform-based methods have shown promising results in characterizing weak seismic events at multiple scales, especially for abundant microearthquakes induced by hydraulic fracturing in unconventional and geothermal reservoirs or foreshock and aftershock activity potentially preceding tectonic earthquakes. This review presents a comprehensive summary of the current status of waveform-based location methods, through elaboration of the methodological principles, categorization, and connections, as well as illustration of the applications to natural and induced/triggered seismicity, ranging from laboratory acoustic emission to field hydraulic fracturing-induced seismicity, regional tectonic, and volcanic earthquakes. Taking into account recent developments in instrumentation and the increasing availability of more powerful computational resources, we highlight recent accomplishments and prevailing challenges of different waveform-based location methods and what they promise to offer in the near future.

Authors:
Coman A., Manea E.F., Cioflan C.O., Radulian M.

Abstract:
The purpose of this study is to identify and to map the fundamental frequency of resonance for the Transylvanian Basin using the computation of H/V spectral ratios from 20 three-component single station measurements of ambient vibrations. This spectral curve exhibits multiple peaks suggesting lateral variations within the subsoil of this area. The fundamental frequency of resonance along Transylvanian Basin varies from very low values (0.07 Hz) up to 11.2 Hz. For some stations, higher mode peaks are detected in the frequency domain of 0.35-4.9 Hz.

Authors:
Coman A., Manea E.F., Cioflan C.O., Radulian M.

Abstract:
The purpose of this study is to identify and to map the fundamental frequency of resonance for the Transylvanian Basin using the computation of H/V spectral ratios from 20 three-component single station measurements of ambient vibrations. This spectral curve exhibits multiple peaks suggesting lateral variations within the subsoil of this area. The fundamental frequency of resonance along Transylvanian Basin varies from very low values (0.07 Hz) up to 11.2 Hz. For some stations, higher mode peaks are detected in the frequency domain of 0.35-4.9 Hz.

Authors:
Toma-Dănilă D., Armas I., Țigănescu A.

Abstract:
Due to their widespread and continuous expansion, transportation networks are considerably exposed to natural hazards such as earthquakes, floods, landslides or hurricanes. The vulnerability of specific segments and structures among bridges, tunnels, pumps or storage tanks can translate not only into direct losses but also into significant indirect losses at the systemic level. Cascading effects such as post-event traffic congestion, building debris or tsunamis can contribute to an even greater level of risk. To support the effort of modeling the natural hazards' implications at the full transportation network scale, we developed a new applicable framework, relying on (i) GIS to define, analyze and represent transportation networks; (ii) methods for determining the probability of network segments to fail due to natural-hazard effects; (iii) Monte Carlo simulation for multiple scenario generation; (iv) methods to analyze the implications of connectivity loss on emergency intervention times and transit disruption; and (v) correlations with other vulnerability and risk indicators. Currently, the framework is integrated into ArcGIS Desktop as a toolbox entitled “Network-risk”, which makes use of the ModelBuilder functions and is free to download and modify. Network-risk is an attempt to bring together interdisciplinary research with the goal of creating an automated solution to deliver insights on how a transportation network can be affected by natural hazards, directly and indirectly, assisting in risk evaluation and mitigation planning. In this article we present and test Network-risk at the full urban scale for the road network of Bucharest. This city is one of Europe's most exposed capitals to earthquakes, with high seismic-hazard values and a vulnerable building stock but also significant traffic congestion problems not yet accounted for in risk analyses and risk reduction strategies.

Authors:
Crowley H., Despotaki V., Rodrigues D., Silva V., Toma-Danila D., Riga E., Karatzetzou A., Fotopoulou S., Zugic Z., Sousa L., Ozcebe S., Gamba P.

Abstract:
Building exposure and vulnerability models for seismic risk assessment have been the focus of a number of European projects in recent years, but there has never been a concerted effort among the research community to produce a uniform European risk model. The European Commission’s Horizon 2020 SERA project has a work package that is dedicated to that objective, through the development of an exposure model, an associated set of fragility/vulnerability models, and a database of socioeconomic indicators in order to calculate probabilistic integrated seismic risk at a European scale. This article provides details of the development of the first versions of the European exposure model that describe the distribution of the main residential, industrial and commercial building classes across all countries in Europe, as well as their occupants and replacement costs. The v0.1 of the European exposure model has been integrated within the Global Earthquake Model’s global exposure and risk maps. Preliminary analyses using the model show that almost 35% of the residential population in Europe is exposed to a 475-year return period peak ground acceleration (PGA) hazard of at least 0.1 g, thus highlighting the importance of European seismic risk modeling and mitigation.

Authors:
Bala A., Radulian M., Toma-Dănilă D.

Abstract:
Analyzing the partitioning of stress and deformation in active orogenic settings is of fundamental importance for understanding the mechanisms driving the geodynamic evolution and seismicity, particularly in complex orogenic settings. In this respect, a quantitative understanding is obtained by coupling the large-scale geodynamic evolution with partitioning of local deformation and stress patterns derived from analyzing the seismicity character, focal plane solutions and kinematics of genetically related active structures. The goal of the present paper is to investigate the stress field characteristics in relation with the specific geotectonics and seismogenic zones of Romania. The principal stress components are computed by inverting the fault plane solutions provided by a completed and updated catalogue for the crustal earthquakes recorded since 1929 up to 2012. Our investigation is justified to the extent that the basic hypothesis of properly representing the seismic area partitioning by individual clusters of events is relevant at the scale of each earthquake-prone area and from statistical point of view (minimum 20–30 events). The catalogue covers mostly the area in front of the Carpathians Arc: Moesian Platform, Barlad Depression, North Dobrogean Orogen, Southern Carpathians belt (Făgăraş-Câmpulung, Central Southern Carpathian and Danubian seismogenic zones) and western part of Romania (Banat region). The seismicity is sporadic and the available fault plane solutions are less representative for the entire area in the inner side of the Carpathians and for the Dobrogea region, located between Danube river and Black Sea. Therefore, for these last two regions the resulted stress field properties are considered as preliminary. The formal stress inversion applied on groups of focal mechanisms proved to be a better estimation of the tectonic stress orientation that can be achieved in the study region in comparison with single focal mechanism, as shown in the World Stress Map Project 2016.

Authors:
Mărmueanu G., Borcia I.S., Mărmureanu A., Cioflan C.O., Toma-Dănilă D., Ilieș I., Craiu G.M., Stoian I.

Abstract:
We report on peak ground accelerations (PGAs) recorded for three strong earthquakes in Vrancea, Romania (August 30, 1986, moment magnitude Mw = 7.1; depth h = 131.4 km; May 30, 1990, Mw = 6.9 depth 90.9 km; May 31, 1990, Mw = 6.4 depth 86.9 km & October 28, 2018, Mw = 5.5 depth 147.8 km). The PGAs increase with increasing epicentral distance, and then decrease for larger distances. These real data may be a new chalenge for the probabilistic seismic hazard studies or other methodologies, which take the epicentral PGA as a basic input parameter. To our knowledge, this phenomenom has not been reported elsewhere. Its spatial regularity leaves open the possibility of ascribing it to the soil particularities, like non-linearities.

Authors:
Bălan S.F., Țigănescu A., Apostol B.F.

Abstract:
The paper intends to evaluate and analyze the accelerometric data recorded on certain buildings located in the Bucharest metropolitan area, one of the most exposed in Europe, with three strong earthquakes with magnitude MW>7 in the last century. Starting from information comprised by databases for soils and buildings existing in Bucharest, certain types of structures were selected, according to their specificity (old buildings, retrofitted, etc.) and being continuously seismic monitored. The selected three buildings are equipped with seismic isolators and viscous dampers. The response of these structures, at the ground level, subjected to medium intensity earthquakes will be discussed in terms of peak accelerations and spectral accelerations. Based on the currently accepted standpoint that the dynamic response of certain structures subjected to earthquakes is strongly dependent of the ratio between the natural period of the structure and the dominant period at the construction site, a comparative analysis against free-field data is presented. There would be presented the improvement of seismic response of isolated buildings in Bucharest and the reason these buildings were protected choosing this method. The aim is to provide warnings regarding the severity of seismic events, by means of characteristics of the ground motion, gathered from the response spectra, which may be given soon after the seismic event took place. All the data recorded on instrumented structures during two seismic events (MW = 5.5 and MW = 4.8), together with the subsequent analysis, can represent a reference study for future earthquakes with similar magnitude. The integration of near-realtime seismology with performance-based earthquake engineering allows for providing the information useful for earthquake engineers and decision makers and can enhance the mitigation of seismic risk.

Authors:
Lecocq T., Hicks S.P., Van Noten K., Van Wijk K., Koelemeijer P., De Plaen R.S.M., Massin F., Hillers G., Antony R.E., Apoloner M.T., Arroyo-Solorzano M., Assink J.D., Buyukakpinar P., Cannata A., Cannovo F., Carrasco S., Caudron C., Chaves E.J., Cornwell D.G., Craig D., Den Ouden O.F.C., Diaz J., Donner S., Evangelidis C.P., Evers L., Fauville B., Fernandez G.A., Giannopoulos D., Gibbons S.J., Girona T., Grecu B., Grunberg M., Hetenyi G., Horleston A., Inza A., Irving J.C.E., Jamalreyhani M., Kafka A., Koymans M.R., Labedz C.R., Larose E., Lindsey N.J., McKinnon M., Megies T., Miller M.S., Minarik W., Moresi L., Marquez-Ramirez V.H., Mollhoff M., Nesbitt I.M., Niyogy S., Ojeda J., Oth A., Proud S., Piulli J., Retailleau L., Rintamaki A.E., Satriano C., Savage M.K., Shani-Kadmiel S., Sleeman R., Sokos E., Stammler K., Stott A.E., Subedi S., Sorensen M.B., Taira T., Tapia M., Turhan F., Van der Pluijm B., Vanstone M., Vergne J., Vuorinen T.A.T., Warren T., Wassermann J., Xiao H.

Abstract:
Noise from trains, airplanes, industrial processes, and other sources is recorded on seismometers worldwide. Disentangling this noise is important for extracting out natural signals, but the noise can also roughly track population movements. Lecocq et al. compiled seismic observations around the world and found a substantial decrease in noise resulting from lockdown measures imposed in response to the coronavirus disease 2019 pandemic (see the Perspective by Denolle and Nissen-Meyer). These observations tightly correspond to when the measures went into effect and offer a way to track aggregate behavior. This quiet period also offers the chance to extract anthropogenic sources of noise from those of natural processes.

Authors:
Manea E.F., Cioflan C.O., Coman A., Michel C., Poggi V., Fah D.

Abstract:
Local site evaluation is an essential step in understanding the amplification of seismic motion induced by the complex geological structure and their estimation for future strong earthquakes in urban regions. One of the critical parameters on evaluating amplification effects is the depth of the geophysical bedrock, whose interface to soft sediments is responsible for the development of destructive resonance phenomena. The present study is focused on the estimation of the geophysical bedrock depth along the extra-Carpathian area of Romania (Moesian Platform and surroundings) by correlating and interpolating the results obtained from single station measurements with the available geological/geophysical data. Each site was investigated through the computation of horizontal-to-vertical (H/V) spectral ratios from three-component single station measurements of ambient vibrations. The geophysical bedrock depth was computed using a two-step inversion scheme, based on the retrieval of the Rayleigh-wave ellipticity peak at each seismic station using a regional generic velocity profile. The fundamental frequency of resonance reaches the lowest value in the deepest side (0.07 Hz) and is rising to 13 Hz in the South of the Moesian Platform, where a shallow bedrock is present. The computed bedrock depths (from 30 to ~ 3100 m) show a dipping tendency towards the Southern Carpathians and complex features such as local outcrops and lateral depth variations superpose this gradually dipping trend. In the Carpathian foreland, the bedrock is interpreted as the transition between different sediment layers of Neogene, while outside this area as the Neogene—Cretaceous transition.

Authors:
Apostol B.F.

Abstract:
The problem of vibrations generated in a homogeneous and isotropic elastic half-space by spatially concentrated forces, known in Seismology as (part of) the Lamb problem, is formulated here in terms of Helmholtz potentials of the elastic displacement. The method is based on time Fourier transforms, spatial Fourier transforms with respect to the coordinates parallel to the surface (in-plane Fourier transforms) and generalized wave equations, which include the surface values of the functions and their derivatives. This formulation provides a formal general solution to the problem of forced elastic vibrations in the homogeneous and isotropic half-space. Explicit results are given for forces derived from a gradient, localized at an inner point in the half-space, which correspond to a scalar seismic moment of the seismic sources. Similarly, explicit results are given for a surface force perpendicular to the surface and localized at a point on the surface. Both harmonic time dependence and time pulses are considered (where stands for the Dirac delta function). It is shown that a -like time dependence of the forces generates transient perturbations which are vanishing in time, such that they cannot be viewed properly as vibrations. The particularities of the generation and the propagation of the seismic waves and the effects of the inclusion of the boundary conditions are discussed, as well as the role played by the eigenmodes of the homogeneous and isotropic elastic half-space. Similarly, the distinction is highlighted between the transient regime of wave propagation prior to the establishment of the elastic vibrations and the stationary-wave regime.

Authors:
Petrescu L., Pondrelli S., Salimbeni S., Faccenda M.

Abstract:
The Alpine chain in western and central Europe is a complex orogen developed as a result of the African–Adriatic plate convergence towards the European continent and the closure of several Tethys oceanic branches. Seismic tomography studies detected high-wave-speed slabs plunging beneath the orogen to variable depths and a potential change in subduction polarity beneath the Central Alps. Alpine subduction is expected to leave a significant imprint on the surrounding mantle fabrics, although deformation associated with the Hercynian Orogeny, which affected Europe prior to the collision with Adria, may have also been preserved in the European lithosphere. Here we estimate SKS anisotropy beneath the central and greater Alpine region at 113 broadband seismic stations from the AlpArray experiment as well as permanent networks from Italy, Switzerland, Austria, Germany, and France. We compare the new improved dataset with previous studies of anisotropy, mantle tomography, lithospheric thickness, and absolute plate motion, and we carry out Fresnel analysis to place constraints on the depth and origin of anisotropy. Most SKS directions parallel the orogen strike and the orientation of the Alpine slabs, rotating clockwise from west to east along the chain, from −45 to 90∘ over a ∼700 km distance. No significant changes are recorded in Central Alps at the location of the putative switch in subduction polarity, although a change in direction variability suggests simple asthenospheric flow or coupled deformation in the Swiss Central Alps transitions into more complex structures beneath the Eastern Alps. SKS fast axes follow the trend of high seismic anomalies across the Alpine Front, far from the present-day boundary, suggesting slabs act as flow barriers to the ambient mantle surrounding them for hundreds of km. Further north across the foreland, SKS fast axes parallel Hercynian geological structures and are orthogonal to the Rhine Graben and crustal extension. However, large splitting delay times (>1.4 s) are incompatible with a purely lithospheric contribution but rather represent asthenospheric flow not related to past deformational events. West of the Rhine Graben, in northeastern France, anisotropy directions are spatially variable in the proximity of a strong positive seismic anomaly in the upper mantle, perhaps perturbing the flow field guided by the nearby Alpine slabs.

Authors:
Kinscher J.L., De Santis F., Poiată N., Bernard P., Palgunadi K.H., Contrucci I.

Abstract:
Seismic repeaters are a phenomenon rarely observed in mining environments. In this study, we show that repeaters and associated aseismic slip can be the governing mechanism behind seismic triggering in response to excavation mining, providing new perspectives for rethinking and improving standard procedures for seismic rock burst hazard assessment and mining monitoring. Evidence comes from an extensive multiplet analysis on dense spatiotemporal microseismic event clusters (−2.5 < Mw < 1) that was recorded by a local microseismic network at the Lappberget orebody in the Garpenberg mine in Sweden at around 1 km depth. Analysis involved template matching, clustering, double-difference relocation, source parameter and mechanism estimation, as well as interevent time analysis. The results show that almost 80 per cent of the analysed events can be interpreted as seismic repeaters. Source mechanisms demonstrate systematic strike-slip faulting with a significant reverse faulting component, indicating that triggering of the repeaters is sensitive to increases in the horizontal compressive stresses. We suggest that seismic repeaters represent brittle frictional parts (asperity) of creeping, planar shaped, pre-exiting structures of several metres composed of weak rock-mass materials (e.g. talc) associated with strengthening friction behaviours. This repeater model and the here used definition of asperity thus slightly differs from its meaning in classical seismological models where repeating events are related to the locked fault patches along a creeping fault. In addition, we identified different asperity types for the different repeater families that we interpret as different friction properties. Some multiplet families represent rather a transitional case between multiplet and repeater occurrences that might imply a mixture of weakening and strengthening friction processes, that is, creep and brittle rupture along neighboured plane shaped anisotropies in a heterogeneous rock mass. The exact nature of asperities and seismic and aseismic coupling of the rock mass as well as the propagation mechanism of strain and stress associated with short-term (days to weeks) and long-term (months to years) post-blast creep remains uncertain and needs to be addressed by future investigations. The understanding of these processes is particularly important for assessing hazard of larger dynamic ruptures.

Authors:
Aden-Antoniow F., Satriano C., Bernard P., Poiată N., Aissaoui E.M., Vilotte J.P., Frank W.B.

Abstract:
The 2014 Iquique seismic crisis in Chile, culminating with a Mw 8.1 earthquake on 1 April, highlights a complex unlocking of the Northern Chilean subduction that has been considered a seismic gap since 1877. During the year preceding this event, at least three clusters of seismic activity have been reported: in July 2013 and January and March 2014. Recent studies have proposed large-scale slab deformation as a potential trigger for the megathrust earthquake, and these clusters possibly indicate aseismic slip transients accompanying the progressive destabilization of the plate contact. However, no evidence of gradual unlocking of the interface or transient deformation has yet been found in the seismicity rate. To address this question, we develop a dense earthquake catalog covering 15 months preceding the mainshock and derived from the continuous waveform data set recorded by the Integrated Plate Boundary Observatory Chile (IPOC) and Iquique Local Network (ILN) networks. After declustering the seismicity, a space-time analysis highlights a large-scale acceleration of the seismicity along the interface accompanied by a deceleration of intermediate-depth earthquakes. We demonstrate the existence of a seismic quiescence downdip of the mainshock rupture before the July 2013 cluster. We propose that this seismic quiescence potentially highlights fluid circulation and/or aseismic motion along upper-plate crustal fault(s).

Authors:
Supino M., Poiată N., Festa G., Vilotte J.P., Satriano C., Obara K.

Abstract:
Low-frequency earthquakes are a particular class of slow earthquakes that provide a unique source of information on the physical processes along a subduction zone during the preparation of large earthquakes. Despite increasing detection of these events in recent years, their source mechanisms are still poorly characterised, and the relation between their magnitude and size remains controversial. Here, we present the source characterisation of more than 10,000 low-frequency earthquakes that occurred during tremor sequences in 2012–2016 along the Nankai subduction zone in western Shikoku, Japan. We show that the scaling of seismic moment versus corner frequency for these events is compatible with an inverse of the cube law, as widely observed for regular earthquakes. Their radiation, however, appears depleted in high-frequency content when compared to regular earthquakes. The displacement spectrum decays beyond the corner frequency with an omega-cube power law. Our result is consistent with shear rupture as the source mechanism for low-frequency earthquakes, and suggests a self-similar rupture process and constant stress drop. When investigating the dependence of the stress drop value on the rupture speed, we found that low-frequency earthquakes might propagate at lower rupture velocity than regular earthquakes, releasing smaller stress drop.

Authors:
Bălan S.F., Apstol B.F.

Abstract:
The paper analyses the behaviour of the soil/subsoil characteristics in the Metropolis of Bucharest under seismic movements with the goal of highlighting the potential damage induced by future strong events. For better understanding the specificity of seismic effects from earthquakes originating in Vrancea region were carried out several national and international research works to assess seismic hazard for Bucharest. Will be presented the last results of the 21st century research programs, with a lot of practical results: several drills in the most critical zones of the city, with hundreds of samples on which were done dynamic tests, static ones and downhole measurements for vp and vs profiles. An analysis of the continuously recordings by accelerometers was done, over the Bucharest area. The paper emphasizes the importance of the accumulated data for understanding the dynamic behaviour of the soil under Bucharest and how it influences the impact of future seismic hazards. Better knowledge of seismic hazard will lead to mitigation of building vulnerability to future seismic movements.

Authors:
Apostol B.F., Cune L.C.

Abstract:
Short-term seismic activity in Vrancea is analyzed by means of the inter-event magnitude distributions (distributions of the next seismic event following a conditional seismic event). This seismic activity in Vrancea is fitted by Omori-type time-power laws, with possible correlations over a range of 20−25 days, for magnitudes M < 4−5. Such temporal patterns can be employed in seismic hazard and risk estimation, providing the data set is statistically significant.

Authors:
Vanciu-Rău A., Țigănescu A., Tătaru D., Rău D.

Abstract:
Earthquakes are natural phenomena, triggered by the sudden release of energy inside the Earth, as a result of rock fracturing. Understanding this phenomenon, especially its impact on the built environment, represents a key component of seismic education. A seismic simulator (shake table) was developed in order to facilitate the learning process of the general public and also to bring forward, in an interactive manner, the educational purpose of this instrument. By using this interactive instrument, the basic concepts of seismology and earthquake engineering can be easily explained, such as: ground motion, peak ground acceleration, fundamental period of an earthquake / building and the soil-structure interaction. Moreover, this educational tool can be used to illustrate practical methods of reducing the lateral forces induced in a building subjected to earthquake, by the use of base isolation systems and damping devices. The results of these educational activities can contribute to a better understanding of soil-structure behavior during an earthquake. In addition, it can be underlined how different types of buildings respond to earthquakes, depending on the building and earthquake characteristics and also what means of seismic protection are adequate in the given situation. Using the seismic simulator to demonstrate the physical phenomena that occurs during an earthquake and its effects on buildings, in conjunction with events on seismic risk awareness, can significantly increase the society’s resilience to natural disasters.

Authors:
Constantin A.P., Manea E.F., Moldovan I.A., Partheniu R.

Abstract:
The aim of the present paper is to test intensity attenuation relationships for subcrustal earthquakes occurred in Vrancea (Romania) seismogenic zone in relation with some important dams situated in extra-Carpathian area. During centuries, the Romanian territory has been shaken by strong earthquakes, most of them being centered within Vrancea Zone, which is situated at the bending area of the South-Eastern Carpathians. Most of the zones from extra-Carpathian area are affected by the subcrustal seismic events, where many hydro-technical structures exist, being also exposed to earthquakes action. A detailed analysis of the intensity attenuation laws developed for subcrustal seismic sources was performed using the most recent and complete intensity datasets. We use an extended and combined intensity data including historical and modern, qualitative and quantitative data, i.e. a number of 11 earthquakes occurred during the period 1738-2009 with epicentral/maximum intensities ranging from VII-X MSK degrees, and magnitude Mw from 5.4 to 7.9. All the input data used for testing are resulted after the reevaluation and evaluation of the macroseismic effects produced by the seismic events included in the present study (8697 IDP). The selected attenuation laws were tested for different values of epicentral intensity and with reference to twelve and twenty four azimuthal directions. Besides the testing of the relationships, isoseismal maps based on the selected attenuation laws were accomplished, associated to the biggest possible earthquake (worst scenario) for the Vrancea subcrustal zone, also highlighting the calculated intensities in the selected dam sites. Brief description of the study and used methods. Brief description of the study and used methods.

Authors:
Oros E., Constantinescu E., Paulescu D., Popa M., Plăcintă A.O.

Abstract:
We present a study of the strongest historical earthquakes (Mw > 5.0) occurred in West Romania between 1900 and 1980 to review and homogenize the Romanian Earthquakes and Focal Mechanisms Catalogues on instrumental data basis. New hypocenters relocation, moment magnitudes, Mw and focal mechanisms solutions are obtained on historical instrumental data basis (seismograms, bulletins, catalogues). The vectorized seismograms were analysed to pick up the arrival times of the body and surface waves after careful identification of the phases as a function of the velocity model, first P wave polarity, amplitudes and corresponding periods. We located the hypocenters of 15 events by a grid search algorithm often using S-P differences instead of absolute times. The magnitude was estimated from displacement spectra by the scalar seismic moment method. The focal mechanisms for 9 events were obtained by polarities and sometimes by full-wave inversions depending on the data quality. The solutions based on polarities data are high quality being constrained through the comparative analysis of the observed and computed waveforms. On average, the P axes are NE oriented (N67OE) like the regional trend of the horizontal component of the stress field and the general orientation of the nodal planes

Authors:
Oros E., Plăcintă A.O., Popa M., Rogozea M., Paulescu D.

Abstract:
The purpose of the present study is to elaborate a new model of the macroseismic intensity attenuation using all observed intensities data for the crustal earthquakes in Romania and then, based on this relationship, to calibrate the Bakun-Wentworth method, one of the modern methods most used to estimate the parameters of the historical earthquakes (localization, moment magnitude-Mw). The study is based on 14 calibrating earthquakes (4.5 < Mw < 5.7, 811 IDPs, II < Ii < VIIIO EMS) and 7 validation earthquakes (3.5 < Mw < 5.4, 215 IDPs, II

Authors:
Partheniu R., Craiu A., Diaconescu M., Ioane D., Moldovan I.A.

Abstract:
Previous studies have shown that the Black Sea was subject to tsunami waves generation in the past (Altinok, 1999), with a total of twenty-two events generated. According to recent studies of Diaconescu et al. (2008), the Black Sea is divided in nine seismic sources. A more recent approach structures the area in ten different seismic sources, given by Moldovan et al. (2016, 2017). This study focuses mostly on the Istanbul seismic source, which triggered in the past high magnitude earthquakes followed by tsunami waves. The most recent event generated in the Black Sea was on 15 th of October 2016, with a magnitude Mw = 5.1, at a depth of 10 km, with the following location: Latitude 42.19° N, Longitude 30.68° E. The focal mechanism determined through the moment tensor inversion (U.S. Geological Survey-USGS) indicates a reverse faulting type. For this event, few tsunami modeling scenarios were run. When using the exact parameters of the earthquake (Mw = 5.3), the simulations show no results. More simulations were computed, increasing the magnitude with steps of 0.2, from 7.0 up to 7.8. The modeling was accomplished using the Tsunami Analysis Tool (TAT), software provided by the Joint Research Center (JRC) from Ispra, Italy. The results of these tsunami simulations show low wave heights for a magnitude of 7.2, of maximum 0.42 m in Eregli (Turkey), 0.36 m in Zonguldak Eregli (Turkey), and 0.32 m in Kilimli (Turkey). For a magnitude of 7.6, the maximum wave heights are higher, considered to be moderate, of 1.59 m in Zonguldak Eregli (Turkey), 1.21 m in Eregli (Turkey). Moreover, there are three locations from the Romanian shoreline affected, as follows: 0.83 m in Mangalia, 0.5 m in Techirghiol and 0.39 m in Constanţa. In order to obtain a correlation of these simulations to real events of high magnitude, we will compare them with two past earthquakes from the Istanbul seismic area, generated on 12 th of November 1999 (Mw = 7.2) and 17 th of August 1999 (Mw = 7.6). Due to their location inland, the results for these two earthquakes display very low wave heights, of maximum 0.18 m. These events were also modeled using the same software, same methodology, considering as location an offshore position of the earthquakes, assumed as being generated on similar faults. The results were compared to the modeling output of the 2016 earthquake from October. For a better evaluation of the tsunami waves possibility of occurrence in the Istanbul seismic area, more information regarding the parameters of high magnitude earthquakes, their location and focal mechanism type, are necessary.

Authors:
Radulian M., Dinescu R., Popa M.

Abstract:
The paper brings together all existing data related to seismic monitoring in order to characterize the earthquake-prone areas in Romania. A review of previous works on this subject is also carried out. The impetuous development of the Romanian seismic network in the recent years as number and quality of instruments makes it possible today to identify with a high degree of confidence the geometrical configuration of seismicity patterns able to generate strong earthquakes. At the same time, we are now able to separate the tectonic active zones from those contaminated by human activity and to define with higher accuracy the earthquake-prone areas. By increasing the range of magnitude completeness and by assessing specific variations in time and space of seismicity, the paper brings a significant contribution to improve our ability to evaluate seismic hazard in Romania.

Authors:
Țigănescu A., Bălan S. F., Toma-Dănilă D., Apostol B. F.

Abstract:
The purpose of this research is to analyze the data recorded on instrumented structures in Bucharest and adjacent free-field seismic stations during the last moderate earthquake that occurred on 28th of October 2018 in the Vrancea seismic zone. The earthquake had a 5.5 moment-magnitude, a depth of 147.8 km, and it was felt on a large area of Romania, generating very little damage in Bucharest. In the last five years, the National Institute for Earth Physics has deployed permanent instrumentation (accelerometers) at key stories of five buildings in Bucharest metropolitan area that recorded the seismic motion of the mentioned earthquake. Three of the buildings have been equipped with seismic isolators and dampers and the performance of this earthquake-protection system was assessed based on earthquake data. The data recorded by four free-field seismic stations located in Bucharest were used as reference motion. In order to assess the amplification or reduction of the seismic waves when propagating in the structure, acceleration and velocity data were analyzed, both in time domain and in frequency domain, for selected frequency ranges. The paper presents also the acquisition setup, the dataflow and the data-processing methods. This study highlights the amplification / reduction of the seismic signal recorded at the ground level by the building structure. In the framework of previous studies on data recorded on buildings located in Bucharest, this study adds new valuable information and contribute to a better understanding of seismic response of buildings.

Authors:
Apostol B.

Abstract:
We describe a procedure of determining the seismic-moment tensor from the measurements of the far-field elastic waves (known in Seismology as P and S-waves). These elastic waves are produced by a tensorial point-like force distribution with a short temporal duration (pulse-like time dependence), which corresponds to a double couple representation of the seismic forces. The inverse problem involves more unknowns than (algebraic) equations, and the Kostrov representation is used for the seismic-moment tensor of a faulting source, together with the energy conservation and a covariance condition, in order to reduce the number of unknowns and to determine the system of equations. The explicit solution of this system of equations is obtained and the components of the seismic-moment tensor are given in terms of the far-field elastic waves. Also, the fault geometry and force mechanism are determined.

Authors:
Bala A., Toma-Dănilă D.

Abstract:
In the years 1999 - 2000 two regional seismic refraction lines were performed within a close cooperation with German partners from University of Karlsruhe. One of these lines is Vrancea 2001, with 420 km in length, almost half of them recorded in Transylvanian Basin. The structure of the crust along the seismic line revealed a very complicated crustal structure beginning with Eastern Carpathians and continuing in the Transylvanian Basin until Medias. As a result of the development of the National Seismic Network in the last ten years, more than 100 permanent broadband stations are now continuously operating in Romania. Complementary to this national dataset, maintained and developed in the National Institute for Earth Physics, new data emerged from the temporary seismologic networks established during the joint projects with European partners in the last decades. The data gathered so far is valuable both for seismology purposes and crustal structure studies, especially for the western part of the country, where this kind of data were sparse until now. Between 2009 and 2011, a new reference model for the Earth's crust and mantle of the European Plate was defined through the NERIES project from existing data and models. The database gathered from different kind of measurements in Transylvanian Basin and eastern Pannonian Basin were included in this NERIES model and an improved and upgraded model of the Earth crust emerged for western part of Romania. Although the dataset has its origins in several periods over the last 50 years, the results are homogeneous and they improve and strengthen our image about the depth of the principal boundaries in the crust. In the last chapter two maps regarding these boundaries are constructed, one for mid-crustal boundary and one for Moho. They were build considering all the punctual information available from different sources in active seismic and seismology which are introduced in the general maps from the NERIES project for Romania. The depths maps in the study region are presented with all their regional peculiarities as they appear, projected on the local tectonic structure for the area under examination.

Authors:
Bala A., Toma-Dănilă D., Radulian M.

Abstract:
Fault plane solutions for earthquakes recorded in Romania (1929–2012) are analysed on three depth levels: crust (0–50 km), upper (50–110 km) and lower segment (110–201 km). For the Vrancea intermediate-depth source reverse faulting is predominant. However, local-scale variations occur at the upper and lower limits of the active volume: normal faulting (upper side) and strike-slip with normal faulting (lower side). These edge effects are probably caused by the interaction of cold descending lithosphere with hot surrounding asthenosphere acting there. Fault plane solutions of crustal earthquakes reflect complicated patterns associated to local stress sources perturbing the regional field. One important result of our analysis is the delimitation of specific active alignments in North Dobrogea Orogen, Bârlad Depression, Danubian and Banat zones, while seismicity is diffuse and close to random distribution in the other seismogenic zones. The polar diagrams for azimuthal and dip angle distributions and the ternary diagrams for P, T and B axes show prevalence of reverse faulting in Vrancea intermediate-depth source, strike-slip in combination with normal faulting in South Carpathians and Banat region and a deficit of strike-slip faulting south-east of Carpathians. Lack of strike-slip component makes us believe that the deformation field is controlled in the Carpathians Foredeep not by transcurrent deformation along the major faults crossing the region, but rather by subsidence and folding processes as stress release mechanisms in the crust in response to the intense tectonic processes beneath Vrancea region.

Authors:
Toader V.-E., Biagi P. F., Moldovan I. A., Mărmureanu A., Mihai A.

Abstract:
The solar radiation affects the life on Earth and it is important in meteorology, climatology, solar energy, agriculture, hydrology and seismology, too. The Sun warms the earth which reflects a part of the energy. An effect of tectonic stress increases the ground temperature that is radiated into the atmosphere. We study the possibility to use the variation of reflected energy in correlation with seismicity, radon concentration, CO2 emission, ULF radio waves, telluric currents, air ionization, temperature in borehole and acoustic noise. In this case, the solar radiation is a precursor factor. This research is important to study the effects of climate change. Analyzing the solar energy budget we find information about the atmosphere: aerosols, ozone, sulfur dioxide, carbon dioxide, nitrogen dioxide and pollution. Our multidisciplinary network (AeroSolSys) monitors Vrancea, a Romanian area characterized by deep earthquakes. For this study, we use two stations, Plostina and Vrancioaia, where we have a net radiometer and a pyranometer. The first sensor includes two pyranometers (up and low) and two pyrgeometers (up and low), a Pt-100 and a Thermistor. The spectral range covers both the Solar Radiation, 0.3 to 3 micrometers, and the Far Infrared Radiation, 4.5 to 42 micrometers. In this case, we measure and determine the temperature of sensor necessary for pyrgeometers, pyranometer short-wave radiation up and low EyU - EyL, pyrgeometers long-wave radiation up and low EgU - EgL, Albedo, net solar radiation NSR, net far infrared radiation NFIR, net total radiation NTR, sky temperature SkyT and, land surface temperature LST. In Vrancioaia, we have a pyranometer with range 0.3 – 2.8 micrometers and maxim 1600 W/m2. Two video cameras monitor the sky and the measurements are correlated with meteorological equipment installed in each location. We use information about solar activity from NOAA satellites and Copernicus CAMS. The humidity of ground is important in energy budget and it is estimated from meteorological data and telluric currents. The interval of analysis is 3 hours, between 2016.01.01 – 2018.05.31. It is difficult to notice the effect of tectonic stress since the daily and seasonal variations of solar radiation are high but global warming is obvious. Solar radiation monitoring helps us to understand other phenomena like radon emission or air ionization.

Authors:
Bălan S.F., Țigănescu A., Apostol B.F., Dăneț A.

Abstract:
Post-earthquake crisis management is a key capability for a country to be able to recover after a major seismic event. Instrumental seismic data transmitted and processed in a very short time can contribute to better management of the emergency and can give insights on the earthquake's impact on a specific area. Romania is a country with a high seismic hazard, mostly due to the Vrancea intermediate-depth earthquakes. The elastic acceleration response spectrum of a seismic motion provides important information on the level of maximum acceleration the buildings were subjected to. Based on new data analysis and knowledge advancements, the acceleration elastic response spectrum for horizontal ground components recommended by the Romanian seismic codes has been evolving over the last six decades. This study aims to propose a framework for post-earthquake warning based on code spectrum exceedances. A comprehensive background analysis was undertaken using strong motion data from previous earthquakes corroborated with observational damage, to prove the method's applicability. Moreover, a case-study for two densely populated Romanian cities (Focsani and Bucharest) is presented, using data from a $5.5M_W$ earthquake (October 28, 2018) and considering the evolution of the three generations of code-based spectral levels for the two cities. Data recorded in free-field and in buildings were analyzed and has confirmed that no structural damage occurred within the two cities. For future strong seismic events, this tool can provide useful information on the effect of the earthquake on structures in the most exposed areas.

Authors:
Besuțiu L., Diaconescu M., Zlăgnean L., Craiu A.

Abstract:
The Galati-Izvoarele region, located in eastern Romania, came into the public attention relatively recent, when hosted an unusual intense earthquake sequence. During September–November 2013, several hundred shallow crust earthquakes were recorded in the area. There were several attempts to explain the phenomenon, and hypotheses more or less documented have been formed. Some speculations occurred on the potential connection between the seismic swarm and oil industry activities. The paper summarizes the results of local geophysical surveys conducted in the area, jointly analysed with the observed seismicity. The main results of the study reveal the Galati-Izvoarele region as a seismic-active area belonging to the northwest prolongation of North Dobrogea mobile zone. The earthquakes were generated mainly in a highly fragmented local graben-like structure, transversally superposed on the descending slope of the North Dobrogea Promontory. The graben fault system was and might be (re)activated each time when tectonic forces acting in the Carpathians foreland intensify. Changes in the intensity of tectonic forces may reflect in the slip acceleration along Peceneaga–Camena Fault, as observed at the Baspunar Geodynamic Observatory. For example, the paroxysmal phase of the Galati-Izvoarele swarm was shortly preceded by a significant increase of the Peceneaga–Camena Fault slip rate recorded at Baspunar Geodynamic Observatory. To conclude, the Galati-Izvoarele region must be seen as a seismic-prone area and any significant increase of the tectonic stress in the Carpathians foreland may generate another seismic sequence in an unpredictable future.

Authors:
Manea E.F., Predoiu A., Cioflan C.O., Diaconescu M.

Abstract:
In this study, we mapped the depth of the fundamental frequency of resonance for the Moldavian and Scythian Platforms using the available data at 18 seismic stations. Each site was investigated through the computation of H/V spectral ratios from three-component single station measurements of ambient vibrations. The observed resonance peaks were interpreted according with the available geological information.

Authors:
Mărmureanu A., Moldovan I.A., Toader V.E., Mărmureanu G.H.,Ionescu C.

Abstract:
The seismic early warning system (SEWS) in Romania uses a mixed regional approach, based on the national seismic network and local sensors to obtain a fast location for recorded events and estimate the actual earthquake magnitude. In order to assess the performance of the alarm system for the 3 dams studied in this paper: Poiana Uzului – Bacău County, Râpa Albastra – Vaslui County and Izvorul Muntelui – Neamț County, there have been made offline simulations on seismic recordings for estimating the actual warning time in the three locations mentioned above. There have been chosen four representative earthquakes ML > 5.0, occurred in the last years in Vrancea seismic zone, for which there are enough records, one crustal from 23rd of September 2017 (ML = 5.7) and three subcrustal from: 22nd November 2016 (ML = 5.8), 27th December 2016 (ML = 5.8) and 2nd February 2017 (ML = 5.0).

Authors:
Mihai A., Moldovan I.A., Toader V.E., Radulian M., Plăcintă A.O.

Abstract:
In the present paper, a relationship between geomagnetic anomalies recorded at one magnetometer located inside Vrancea seismogenic zone and the occurrence of intermediate earthquakes is examined. To better distinguish the regional anomalies from global geomagnetic storms, the datasets were correlated with the geomagnetic indices taken from NOAA/Space Weather Prediction Center. During five years of investigations (2013–2018), three intermediate depth earthquakes with a moment magnitude Mw larger than 5.0 occurred in the Vrancea zone and were accompanied by significant anomalies on the E-W component of the local geomagnetic field (By) measured at Muntele Rosu (MLR) Observatory. The anomalies recorded at MLR were also analyzed along with the seismic energy distribution, providing good opportunity to distinguish the anomaly morphology, and were correlated with the radon emissions and temperature variations, during the detector operating time, in 2016.

Authors:
Nicolae V., Talianu C., Andrei S., Antonescu B., Ene D., Nicolae D., Dandocsi A., Toader V.E., Ștefan S., Savu T., Vasilescu J.

Abstract:
In this study, AERONET (Aerosol Robotic Network) and EARLINET (European Aerosol Research Lidar Network) data from 17 collocated lidar and sun photometer stations were used to characterize the optical properties of aerosol and their types for the 2008–2018 period in various regions of Europe. The analysis was done on six cluster domains defined using circulation types around each station and their common circulation features. As concluded from the lidar photometer measurements, the typical aerosol particles observed during 2008–2018 over Europe were medium-sized, medium absorbing particles with low spectral dependence. The highest mean values for the lidar ratio at 532 nm were recorded over Northeastern Europe and were associated with Smoke particles, while the lowest mean values for the Angstrom exponent were identified over the Southwest cluster and were associated with Dust and Marine particles. Smoke (37%) and Continental (25%) aerosol types were the predominant aerosol types in Europe, followed by Continental Polluted (17%), Dust (10%), and Marine/Cloud (10%) types. The seasonal variability was insignificant at the continental scale, showing a small increase in the percentage of Smoke during spring and a small increase of Dust during autumn. The aerosol optical depth (AOD) slightly decreased with time, while the Angstrom exponent oscillated between “hot and smoky” years (2011–2015) on the one hand and “dusty” years (2008–2010) and “wet” years (2017–2018) on the other hand. The high variability from year to year showed that aerosol transport in the troposphere became more and more important in the overall balance of the columnar aerosol load

Authors:
Partheniu R., Ghiță C., Toader V.E., Năstase E., Muntean A., Murat E., Moldovan I.A., Ionescu C.

Abstract:
The Black Sea is prone area to natural hazards: earthquakes, tsunamis, storms, strong winds and other meteorological conditions. In order to monitor them, the National Institute for Earth Physics (NIEP) has installed different types of equipments, implemented into a system that can send warnings for tsunamis and earthquakes generated in the Black Sea. As part of the routine monitoring, the first tsunami early-warning system in the Black Sea was accomplished in 2013, providing sea level and seismic data exchange with the Black Sea surrounding countries. A number of 3 sea level monitoring stations and 7 GPS/GNSS stations are installed in different locations in Dobrogea area. An infrasound micro-barometer, a meteorological station and a vertical electric field monitor were also installed. Various parameters are measured, from water level variations to temperature, wind speed and direction, precipitations, etc. In order to centralize all data, a web portal for worldwide and regional tsunami monitoring was developed (tsunami.infp.ro), with a focus on the Black Sea. Some other objectives of NIEP are to continue monitoring the natural hazards triggered in the area, to increase regional and international collaboration, and to add seismic, GPS/GNSS, sea level and other equipment to the existing network.

Authors:
Petrescu L., Stuart G., Tătaru D., Grecu B.

Abstract:
The structure and processes of collisional orogens at the edges of cratons are complex and the extent to which the crust is affected by subduction of cratonic material, slab break-off and post-collisional magmatism is poorly constrained. The Carpathian arc is an Alpine orogenic system, involving the collision and subduction of the East European Craton and the closure of the Tethys ocean. Unusual Neogene backarc magmatism developed after subduction ended ∼9 Ma ago and upper-mantle Mw>7 earthquakes are associated with a relic slab actively breaking-off in the Vrancea Zone. To investigate the crustal and uppermost mantle structure, we analyse teleseismic earthquakes recorded at 56 broad-band seismic stations in Romania and Moldova. Using phase-weighted H − κ stacking of receiver functions, we estimate the bulk crustal thickness and Vp/Vs ratio, a good discriminant of crustal composition. This technique was used on all stations and assumes a single-layer crust with a discontinuity at its base. Additionally, by jointly inverting receiver functions and ambient noise we obtain shear wavespeed (Vs) models to ∼60 km depth beneath 34 stations and provide another independent measure of the Moho depth and its apparent seismic sharpness. Crustal thickness estimates from the two methods are inconsistent in regions where the Moho is gradational or an intracrustal discontinuity is more dominant. We support this interpretation with a range of synthetic tests. Above the actively detaching Vrancea slab, multiple intracrustal discontinuities and a gradational Moho are identified on Vs profiles, and high Vp/Vs (>1.83) are consistent with magmatic underplating. On the backarc side of the slab, magmatism-pervaded crust has low Vp/Vs signature (<1.73), consistent with felsic composition or the presence of water without extensive partial melt. In the backarc Transylvanian Basin and Apuseni Mountains, the upper mantle has anomalously low Vs (<4 km s−1 to 60 km depth), the crust is dominantly felsic and thin (<35 km), with a Moho probably inherited from the obducted Neo-Tethys ophiolites. On the forearc side, sedimentary basins have low Vs (<2.5 km s−1) and high Vp/Vs signatures (>1.8), indicating a high fluid-pressure regime. Finally, Precambrian units in the foreland are seismically heterogenous, with Moho depths of 30–50 km, and extend ∼100 km beneath the South and Southeast Carpathians, implying that the Vrancea slab underlies Precambrian-aged crust.

Authors:
Radulian M., Bala A., Ardeleanu L., Toma-Dănilă D., Petrescu L., Popescu E.

Abstract:
The purpose of this paper is to present the most comprehensive catalogue of focal mechanisms for Romanian earthquakes which occurred between 1929 and 2000 in the Carpathian Orogen, the Moesian and Moldavian Platforms, and the Transylvanian Basin. The present catalogue (REFMC) is a first step toward creating a centralized and continuous database of earthquake mechanisms in Romania by revising and updating existing data for the twentieth century, which together with the Romanian earthquake catalogue (ROMPLUS)—continuously updated by the National Institute for Earth Physics, provides the fundamental information for any seismicity or seismic hazard assessment. In order to produce a close-to definitive version compatible with more recent and less uncertain focal mechanisms solutions, we revised multiple sets of data (some of which newly found), recalculated and corrected some of the fault-plane solutions and reached a consensus. The catalogue comprises 250 crustal events and 416 intermediate-depth events recorded in the twentieth century starting from 1929. On the basis of the new catalogue data and seismotectonic investigation, we propose a reconfiguration of the seismogenic zones located along Southern Carpathians toward the western side of Romania.

Authors:
Zoran M., Savastru R., Savastru D., Mateciuc D.

Abstract:
This paper investigates earthquake precursors which can be detected from geospatial time series data in synergy with ground monitoring data. Have been analyzed air and land surface temperature anomalies, Aerosol Optical Depth (AOD) variations as well as anomalies recorded by outgoing long-wave radiation and latent heat flux from TIR (Thermal InfraRed) from MODIS Terra/Aqua, NOAA AVHRR, Landsat TM/ETM/OLI and Sentinel 1/ 2 data. Also have been located ground surface deformations detected through Synthetic Aperture Radar Interferometry (InSAR) radar satellite (Sentinel 1) and high quality in-situ GPS monitoring data as well as in-situ monitoring of radon in air near the ground for some moderate earthquakes recorded during 2012 – 2016 period in Vrancea active region in Romania. As Vrancea zone in Carpathians has a significant regional tectonic activity in Romania and Europe, the joint analysis of satellite and field geophysical information is revealing new insights in seismic hazard assessment.

Authors:
Toader V.E., Moldovan I.A., Mihai A

Abstract:
The solar radiation affects the life on Earth and it is important in meteorology, climatology, solar energy, agriculture, hydrology and seismology, too. The Sun warms the earth which reflects a part of the energy. An effect of tectonic stress increases the ground temperature that is radiated into the atmosphere. We study the possibility to use the variation of reflected energy in correlation with seismicity, radon concentration, CO2 emission, ULF radio waves, telluric currents, air ionization, temperature in borehole and acoustic noise. In this case, the solar radiation is a precursor factor. This research is important to study the effects of climate change. Analyzing the solar energy budget we find information about the atmosphere: aerosols, ozone, sulfur dioxide, carbon dioxide, nitrogen dioxide and pollution. Our multidisciplinary network (AeroSolSys) monitors Vrancea, a Romanian area characterized by deep earthquakes. For this study, we use two stations, Plostina and Vrancioaia, where we have a net radiometer and a pyranometer. The first sensor includes two pyranometers (up and low) and two pyrgeometers (up and low), a Pt-100 and a Thermistor. The spectral range covers both the Solar Radiation, 0.3 to 3 micrometers, and the Far Infrared Radiation, 4.5 to 42 micrometers. In this case, we measure and determine the temperature of sensor necessary for pyrgeometers, pyranometer short-wave radiation up and low EyU - EyL, pyrgeometers long-wave radiation up and low EgU - EgL, Albedo, net solar radiation NSR, net far infrared radiation NFIR, net total radiation NTR, sky temperature SkyT and, land surface temperature LST. In Vrancioaia, we have a pyranometer with range 0.3 – 2.8 micrometers and maxim 1600 W/m2. Two video cameras monitor the sky and the measurements are correlated with meteorological equipment installed in each location. We use information about solar activity from NOAA satellites and Copernicus CAMS. The humidity of ground is important in energy budget and it is estimated from meteorological data and telluric currents. The interval of analysis is 3 hours, between 2016.01.01 – 2018.05.31. It is difficult to notice the effect of tectonic stress since the daily and seasonal variations of solar radiation are high but global warming is obvious. Solar radiation monitoring helps us to understand other phenomena like radon emission or air ionization.

Authors:
Apostol B.

Abstract:
This paper presents the solution of an inverse problem in Seismology, which aims at deriving the seismic source parameters from P and S seismic waves. In particular, the paper gives the deduction of the seismic-moment tensor. The problem is tackled in this paper under three particular circumstances. First, we use the amplitude of the far-field (P and S) seismic waves as input data. We use the analytical expression of the seismic waves in a homogeneous isotropic body with a seismic-moment source of tensorial forces, the source being localized both in space and time. We assume that the position of the seismic source is known. The far-field waves provide three equations for the six unknown parameters of the general tensor of the seismic moment, such that the system of equations is under-determined. Second, the Kostrov vectorial (dyadic) representation of the seismic moment for a shear faulting is used. This representation relates the seismic moment to the focal displacement in the fault and the orientation of the fault (moment-displacement relation); it reduces the seismic moment to four unknown parameters. Third, the fourth missing equation is derived from the energy conservation and the covariance condition. The four equations derived here are solved and the seismic moment is determined, as well as other parameters of the seismic source, like focal volume, focal slip, fault orientation, and duration of the seismic activity in the source. It turns out that the seismic moment is traceless, its magnitude is of the order of the elastic energy stored in the focal region (as expected), and the solution is governed by the unit quadratic form associated with the seismic-moment tensor (related to the magnitude of the longitudinal displacement in the P wave). A useful picture of the seismic moment is the conic represented by the associated quadratic form, which is a hyperbola (seismic hyperbola). This hyperbola provides an image for the focal region: its asymptotes are oriented along the focal displacement and the normal to the fault. Also, the special case of an isotropic seismic moment is presented. Numerical examples are provided for this procedure, and the limitations are discussed.

Authors:
Zoran M.A., Savastru R.S., Savastru D.M., Mateciuc D.N.

Abstract:
The main problem for seismic precursors recognition is to extract useful information associated with tectonic activities and to eliminate the effects of non-tectonic factors. Pre-earthquake spatio-temporal developed geophysical, geodetically, and geochemical anomalies are controlled by various factors like as earthquake moment magnitude and its focal depth, geological setting, topography, land covers as well as climate and atmospheric conditions. In this paper, changes before and after some moderate Vrancea earthquakes in the crustal dynamics as well as in the land and atmospheric parameters (surface air temperature- AT and land surface temperature LST anomalies, have been investigated on the basis of timeseries geospatial (NOAA AVHRR and MODIS Terra/Aqua) and field data analysis for 2010-2018 period. Ground surface deformations have been detected through analysis of Synthetic Aperture Radar Interferometry (InSAR) radar satellite Sentinel 1 and high quality in-situ GPS monitoring data. The detected changes show strong evidence of coupling between lithosphere-land surface-atmosphere-ionosphere associated with the Vrancea’s earthquakes For some analyzed earthquakes, starting with ten days up to one week prior to a moderate earthquake a transient thermal infrared rise appeared in AT (2-10°C) and LST (20-30°K) higher than the normal values, function of the magnitude and focal depth, which disappeared after the main shock. Ground vertical surface displacements presented on interferometric deformation map are in the range of 4 cm for uplifts and subsidence. The joint analysis of geospatial, geophysical, and geological information is revealing new insights for Vrancea zone seismicity understanding.

Authors:
Mihai A., Moldovan I.A., Toader V.E., Petrescu L., Partheniu R.

Abstract:
In this study were used geomagnetic data recorded during last 5 years, from 2013 till present. The records were corrected for missing and wrong data induced by malfunction of the data acquisition system. The main purpose of the paper is to identify the magnetic field behaviour in relation with space weather, meteorological phenomenon including annual/diurnal temperature variation, local and regional seismic activity. The paper is focusing on geomagnetic anomalies detected on the recorded field at one magnetometer located near Vrancea seismogenic zone prior to Mw>4.5 crustal and intermediate depth earthquakes. During these 5 years of investigations one crustal earthquake and three subcrustal earthquakes with a moment magnitude Mw between 5.0 and 6.0, occurred in the Vrancea zone. All three intermediate depth events were accompanied by significant anomalies on Y axis (EW component) of local geomagnetic field measured at MLR observatory. The MLR magnetometer was outside the preparation zone of the crustal earthquake, located at 100km distance from the epicenter, so no anomaly was observed. In order to highlight the anomalies recorded at Muntele Rosu (MLR) seismological observatory, these data were compared with data from Surlari (SUA) observatory, located about 150 Km South-East outside the Vrancea seismogenic zone. Similarly, earthquakes with Mw between 4.5 and 5 are accompanied by same type but smaller amplitude anomalies, were the drop on Y axis was less than 10 nT instead of 20-30 nT as those occurred prior to earthquakes with Mw>5.0. The latter ones are harder to observe during the summer time when these anomalies are hidden by large diurnal variations. The anomaly duration extends from days to sometimes months, without correlation with the earthquake magnitude. To better distinguish the local/regional anomalies from global geomagnetic behaviour, both MLR and SUA datasets were also corelated with the geomagnetic indices from NOAA/Space Prediction Center. The presence of geomagnetic storms creates a specific type of anomalies that sometimes might hide the ones related to earthquakes. The geomagnetic measurements were also compared with temperature values recorded at MLR station both for avoiding wrong interpretation of instrument response related to temperature variations, and to highlight possible correlations of magnetic field behaviour with ambient temperature. The three medium sized intermediate earthquakes that have occurred in the studied time interval provided a good opportunity to investigate the link between the presence of anomalies on geomagnetic records at Muntele Rosu observatory and seismicity in Vrancea zone.

Authors:
Oros E., Placinta A. O., Popa M.

Abstract:
The main task of the presented study is to elaborate a set of relations of mutual conversion macroseismic intensity - magnitude, necessary for the calibration of the historical crustal earthquakes produced in the Intra - Carpathian region of Romania, as a prerequisite for homogenization of the parametric catalogue of Romanian earthquakes. To achieve the goal, we selected a set of earthquakes for which we have quality macroseismic data and the Mw moment magnitude obtained instrumentally. These seismic events were used to determine the relations between the Mw and the peak/epicentral intensity, the isoseist surface area for I=3, I=4 and I=5: Mw = f (Imax / Io), Mw = f (Imax / Io, h), Mw = f (A3, A4; A5). We investigated several variants of such relationships and combinations, taking into account that the macroseismic data necessary for the re-evaluation of historical earthquakes in the investigated region are available in several forms. Thus, a number of investigations provided various information resulted after revising initial historical data: 1) Intensity data point (IDP) assimilated or not with the epicentre intensity after analysis of the correlation level with recent seismicity data and / or active tectonics / seismotectonics, 2) Sets of intensities obtained in several localities (IDPs) with variable values having maxims that can be considered equal to epicentral intensity (Io), 3) Sets of intensities obtained in several localities (IDPs) but without obvious maximum values, assimilable with the epicentral intensity, 4) maps with isoseismals, 5) Information on the areas in which the investigated earthquake was felt or the area of perceptiveness (e.g. I = 3 EMS during the day and I = 4 EMS at night) or the surfaces corresponding to a certain degree of well-defined intensity. The obtained relationships were validated using a set of earthquakes with instrumental source parameters (localization, depth, Mw). These relationships lead to redundant results meaningful in the process of estimating the quality and credibility of the primary data used (e.g. IDPs, isoseismals) and in the correct determination of Mw.

Authors:
Tătaru D., Popovici A., Popovici B., Mironoc C., Straticiuc M.

Abstract:
The global development of the society requires a constant updating of the objectives that education pursues, as well as the ways in which they are achieved. STEM education is an area undergoing a process of advanced transformation, both at the level of objectives and methodologies, with a strong social, economic and knowledge impact. Research-based education is a well-established term especially in the higher education system. More and more studies and key policy documents argue that education has to be based on the cutting edge research, while many universities are claiming to place the approach at the core value they believe in. However, different theoretical and methodological perspectives on the subject of research-based education combined with challenges related to the use of different resources and the necessary knowledge on behalf of teachers could make it very difficult to properly use it in the pre-university classroom. Much more natural is to test and asses the research-based teaching and learning outcome in an out-of-the-class setup, such as summer programs for students or extra-curricular activities. In the present study we will describe how a science and technology summer school program could be planned and used as a testbed (pilot) for developing a research-based methodology to teach STEM subjects to highschool students. There are some elements that makes Science and Technology Magurele Summer School unique in the national landscape, mainly because containing the most important ingredients: linking education to a real research environment, being conducted by researchers and builds on existing research on the field. A group of 40 highschool students selected based on previous results and interest in the topics has been “exposed” to science for one week, organized in small groups and working together with mentors (researchers) inside high level research laboratories of research institutes and universities research centers. They had the chance to learn how research is conducted and produces new knowledge, conduct own research as a part of their studies or participate in research projects of the academic staff. 16 themes have been proposed to students to choose from, with topics ranging from engineering to artificial intelligence, from robotics to biotechnology. All the proposed projects tackled a real challenge with a proven impact on daily life, for example how to attack a tumor cell using a high beam laser, how to improve earthquake buildings resistance using antiseismic elements, how to build and launch an environmental monitoring capsule in the stratosphere and measure important parameters as temperature, altitude, position, radiation, pollution, etc. To evaluate the initiative a set of input, process and output indicators that can provide insights to the effects of the link between education and research have been used and assessed. In parallel feedback was collected from a group of teachers to whom methodologies have been presented and who were able to monitor the students at work. The results encourage the extension of the programme, of the topics proposed and period.

Authors:
Partheniu R., Tolea A., Ioane D., Tătaru D., Grecu, B.

Abstract:
On 8th of September 2017, an earthquake of magnitude Mw 8.1 was generated offshore Mexico, Chiapas area, at 04:49 UTC, with a depth of 72 km and the following coordinates: Latitude 15.02 N, Longitude 93.81 W, 98 km away from Pijijiapan (Mexico). The fault plane solution of the event was normal plane. Maximum tsunami waves of 1.1 m were measured at Salina Cruz sea level station, following the earthquake. Tsunami modelling simulations were accomplished using the earthquake's parameters (location, magnitude, depth) and moment tensor solutions given by 3 different agencies: United States Geological Survey (USGS), German Research Centre for Geosciences (GFZ) and Global Centroid Moment Tensor (GCMT). For every case studied, the affected locations, sea level estimates and maximum wave heights were computed. There are two software used for modelling, the Tsunami Analysis Tool (TAT), provided and developed by the Joint Research Centre, Ispra, Italy and TRIDEC Cloud, provided by the German Research Centre for Geosciences (GFZ), Potsdam, Germany. After analysing the modelling scenarios, a comparison between the results of the two software was accomplished, for the same earthquake parameters. The results show that the parameters of GCMT computed with TAT overestimate those computed with TRIDEC, of maximum 3.9 m wave height at Arista with TAT and 2.46 m with TRIDEC. For the GFZ parameters, the estimates give 3.5 m for Pasito de la Senora with TAT, compared to 1.64 m maximum waves at Puerto Madero with TRIDEC. For the USGS data set, the results are similar, maximum waves of 2.4 m at Pasito de la Senora with TAT, and 2.9 m at Puerto Madero with TRIDEC. The Salina Cruz station, where 1.1 m height waves were measured, gives results only for the simulations ran with TAT, with 1.0 m for the GFZ earthquake parameters, 0.6 m for USGS and 1.4 m for the GCMT parameters.

Authors:
Bălă A., Toma-Danila D., Radulian M.

Abstract:
A catalogue of fault plane solutions for earthquakes recorded in Romania between 1929 and 2012 is analyzed in order to outline statistical features of the fault plane solutions in correlation with the earthquake-prone areas in Romania. The catalogue contains both groups: crustal earthquakes (h < 50 km) and intermediate-depth earthquakes (h > 50 km), but only the crustal earthquakes are analyzed here. The catalogue covers mostly the area in front of the Carpathians Arc: Moesian Platform, Barlad Depression, North Dobrogean Orogen and Fagaras ? Campulung, Central Southern Carpathian seismogenic zones. The Intra-Carpathians area has a sparse seismicity and the available fault plane solutions are not enough to derive regional horizontal crustal stress based on multiple mechanism solutions. In our present investigations we have employed the formal stress inversions of a group of focal mechanisms (FMF), which is a better estimation of the tectonic stress orientation that can be achieved in a region with a homogeneous regional stress field, in comparison with single focal mechanism, as shown in World Stress Map Project . The formal stress inversion of multiple focal mechanisms (FMF) improves the quality of stress derivation, but it is linked to two main assumptions: (1) the chosen FMS lies in a region with a uniform stress field that is invariant in space and time; (2) the direction of earthquake slip follows the direction of the maximum shear stress, as in Wallace-Bott hypothesis . The 2D horizontal stress is determined in the crustal zones using local grids with cells containing at least 15- 20 fault plane solutions and is graphically represented, using STRESSINVERSE computer programs with public access .

Authors:
Bălan S.F., Apostol B. F., Tiganescu A.

Abstract:
In this paper will be indicated the different behaviour of buildings in Bucharest, mistakes in design and execution, state of codes and regulations in the XXth century, revealing what went wrong. Several national and international research programs were done in the past to understand the causes for the Vrancea seismicity, to study the seismic wave propagation in the region and to assess seismic hazard for Bucharest and other communities. Especially in Bucharest, high-quality seismic data were acquired obtaining a unique dataset providing important information on the seismic amplitude variations across the area. For site studies of important constructions (social-cultural, administrative, industrial etc.) the designer must follow certain steps to ensure taking into account all the elements that could influence the reliability of future buildings. For this purpose a lot of investigations of seismological evaluations across the city have been carried out with new results given to construction developers.

Authors:
Bălan S.F., Tigănescu A., Apostol B.F.

Abstract:
The paper presents displacements and accelerations of two tower type buildings, one near the epicenter zone, Vrancea and one South of Bucharest (~150 km from epicenter zone). Displacements and accelerations were computed from the processed recorded accelerograms. Were used 3 “Triaxial Seismic Accelerometers” on 3 levels of each building. The displacements and accelerations on the analyzed structures were a result of Vrancea medium earthquakes between 2014-2017 years with magnitudes Mw ranging from 3.8 to 5.6 and depths between ~ 41 km to 147 km. A discussion of structural response was made concerning each building (one on 12 seismic events, the other on 6 ones and both on 4 that are common). The recorded data will contribute to a better understanding of the structures responses, even subjected to medium magnitude seismic events, and to the mitigation of seismic risk for densely populated areas.

Authors:
Biagi P.F., Colella R., Schiavulli L., Ermini A., Boudjada M., Eichelberger H., Schwingenschuh K., Katzis K., Contadakis M.E., Skeberis C., Moldovan I.A., Bezzeghoud M.

Abstract:
VLF/LF (20 - 300 kHz) radio waves propagation is affected by different factors such as meteorological conditions, solar bursts and geomagnetic activity. At the same time, variations of some parameters in the ground, in the atmosphere and in the ionosphere occurring during the preparatory phase of earthquakes can produce disturbances in the propagation of the previous signals along their radio paths: these disturbances are the radio precursors. Since 2009, several VLF/LF radio receivers have been installed throughout Europe in order to realize a European (VLF/LF) radio network for studying the VLF/LF radio precursors of earthquakes, called the INFREP network. In this paper, at first the description of the present situation of the INFREP network is presented, that is: the location of the receivers, the location of the VLF/LF transmitters whose signal is sampled, the daily download of the data collected by the receivers on the INFREP server and the method of data analysis used in order to individuate possible radio precursors. Then the results obtained on the occasion of recent (2016-2017) seismic activities which occurred in the “sensitive” zone of the INFREP network are presented. The first case examined is the October 30, 2016 earthquake with Mw = 6.5, which occurred in Central Italy, near Norcia small town; this earthquake was preceded by a strong shock (Mw = 5.9) which occurred 4 days before. The second case presented is the strong (Mw = 6.7) offshore earthquake which occurred on July 20, 2017, near the coast of Turkey and Kos island (Greece) and the third case is the August 8, 2017 earthquake with Mw = 5.0, which also occurred near the coast of Turkey and Kos island (Greece). In all the previous cases radio anomalies were revealed in some radio signals collected by the receiver located in Cyprus. The influence of causes different from seismicity as geomagnetic activity and solar burst, meteorological conditions, malfunction of the receiver and/or the transmitters has been examined and none convincing connections appeared. So, the possibility that the previous anomalies are radio precursors of the earthquakes seems realistic. Finally, some discrepancy of some of these anomalies with respect to the general peculiarities of the radio precursors is presented and discussed.

Authors:
Zoran M., Savastru R., Savastru D., Mateciuc D.

Abstract:
This paper investigates earthquake precursors which can be detected from geospatial time series data in synergy with ground monitoring data. Have been analyzed air and land surface temperature anomalies, Aerosol Optical Depth (AOD) variations as well as anomalies recorded by outgoing long-wave radiation and latent heat flux from TIR (Thermal InfraRed) from MODIS Terra/Aqua, NOAA AVHRR, Landsat TM/ETM/OLI and Sentinel 1/ 2 data. Also have been located ground surface deformations detected through Synthetic Aperture Radar Interferometry (InSAR) radar satellite (Sentinel 1) and high quality in-situ GPS monitoring data as well as in-situ monitoring of radon in air near the ground for some moderate earthquakes recorded during 2012 – 2016 period in Vrancea active region in Romania. As Vrancea zone in Carpathians has a significant regional tectonic activity in Romania and Europe, the joint analysis of satellite and field geophysical information is revealing new insights in seismic hazard assessment.

Authors:
Constantin A.P., Moldovan I. A., Partheniu R., Manea E. F., Ionescu C.

Abstract:
A correct seismic hazard assessment and intensity-based shake maps of a seismic zone depend on the determination of parameters that emphasize the distribution and the macroseismic intensity attenuation for that seismogenic zone. Due to the reduced number of strong ground motion records, macroseismic intensity information available for previous earthquakes which have occurred in studied area were the only source of information utilized for developing attenuation relationship for that zone. The aim of this paper is to test the existing equations published for various crustal seismic sources and develop a new macroseismic intensity attenuation law for the Vrancea crustal seismic source. The Vrancea crustal seismogenic zone had experienced moderate earthquakes in the past with magnitudes which did not exceed 5.9 [1] and macroseismic maralps had been constructed by various authors for these earthquakes representing intensity pattern and decrease of this parameter with distance on different azimuths. Some of the selected attenuation laws were tested for different values of epicentral intensity and with reference to eight directions. The input data consist of macroseismic intensities collected for 4 small and moderate earthquakes (Mw ≥ 3.9) that had occurred during the last hundred years with epicentral/maximum intensity in the range IV to VI MSK degrees. The seismic events used to verify the attenuation laws were selected based on the magnitude and number of macroseismic observations collected for each event. Using this data, attenuation relationships of macroseismic intensity with distance will be tested and modified. The deduced attenuation equation might be used for rapid intensity assessment of the potential future earthquakes occurred in this seismic zone.

Authors:
Diaconescu M., Ghiță C., Oros E.

Abstract:
The Apuseni Mountains are located in the western part of Romania and are limited to the west by the contact with Pannonian Depression and to the east by the Transylvanian Basin. Basically To the south Apuseni Mountains are bounded by the South Transylvanian Fault and in the northern part by the North Transylvanian Fault. Apuseni Mountains represents an isolated massif inside Carpathian arch, consisting of complex folds and thrust belts formed in Cretaceous period as results of interactions between multiples micropletes separated by Tethys ocean branches. The orogenic system of the Apuseni Mountains can be divided in two parts, in fact two main pre-Neogen structural units: The North Apuseni, composed of an early proterozocic Variscan basement belonging to the Inner Dacides as part of the Tisa geodynamic block and South Apuseni as the as aprt of Dacia Block (his northern part) which include a ophiolitic sequence of the Carpathians. The tectonic regime of the Apuseni Mountains consist of two type, such as: a compressive one, according to the tectonic structures, with SH max predominat oriented NW to SE, and in the marginal area is a predominat extensive tectonic regime. For the Mures Corridor (South Transylvanian Fault) the tectonic regime is strike slip type.

Authors:
Dinescu R., Munteanu I., Placinta A., Dinu C., Oros E., Popa M., Radulian M.

Abstract:

Authors:
Ghita C., Diaconescu M., Craiu A.

Abstract:
The purpose of this work consists in analyses of declustering catalogue and seismic sequence recorded in Vrancea crustal area . The moderate-size earthquake with local magnitude 5,7 which occurred on November 22, 2014 in Vrancea region, at 41 km depth, is the largest crustal event instrumentally recorded at the bending of the Eastern Carpathians. The crust seismicity in front of the Carpathian Arc spreads to the East, in a strip delimited by the Peceneaga-Camena fault, to the North and East, and to the South is lost to the Intramoesica fault. The crust seismicity does not exceed the magnitude of 5.6 (Mw) and it seems to have no relation to the seismic activity of the subduction lithosphere. Seismic activity is characterized by spatial and temporal clustering in the Ramnicu Sarat sub-zones through seismic sequences and swarms in the Vrancioaia area. Using the first version of the software SEDA v.1 [1] we determined the Maximum Likelihood Estimation (MLE) ETAS model on an Vrancea area. The algorithm implemented in SEDAv1.0 is an innovative method based on Simulated Annealing. The Epidemic Type Aftershock Sequences (ETAS) model is the most popular stochastic model used to describe earthquake occurrence, to forecast earthquakes and to detect fluid/magma signals or induced seismicity.

Authors:
Mateciuc, N.D., Bălă A.

Abstract:
The studies for Recent Crustal Movements by the aid of space geodesy techniques are integrated into the researches on the Earth?s crust dynamics, as a reflection of the complex geodynamic phenomena that occur in the crust and in the subcrustal lithosphere. In addition to the fundamental nature, the research in this field presents a practical characteristic, competing alongside geology and geophysics to the shaping of new energy sources or solid mineral substances, to the determination of the soil stability degree in inhabited areas or in those in which large industrial targets and utilities are intended to be placed in. The knowledge of movements affecting the Earth?s upper crust, movements that precede, accompany or follow the eathquakes, is also a topical issue. The paper presents some of the most important research projects developed in Romania, which were based on the measurement data obtained exclusively by space geodesy methods. There are presented some of the most significant results achieved in the framework of each research project together with the limitations imposed by the used acquisition technology. In chronological order are mentioned first GPS measurements in Romania, started in 1994, in a network centered on the Dealul Piscului observer, followed by Romania's involvement in a regional geodynamic project, CERGOP and finally a major international project, CRC461, also continued after 2003 with the continuous help of the University of Delft (Nederlands), a project that led to the development of an extended network of GPS permanent stations in Romania, all in operating status and whose results are a valuable support for the geodynamic studies. There are made brief references to the first application of the Finite Element Method in a GPS subnet from the Vrancea extended network together with some of the most important obtained results.The strong earthquakes with their catastrophic consequences, which have taken place in recent years on a global scale, similar to that of 4 March 1977 in Romania, have fully demonstrated the need for the knowledge of these types of crust movements in order to contribute, together with other methods, to solve the very complex problem of the earthquake forecasting.

Authors:
Mihai A, Moldovan I.A., Toader. V. E.

Abstract:
In this study, the anomalous geomagnetic variation related to the moderate Vrancea earthquake (Mw=5.5) on 28 October 2018 was shown. This anomaly and their associated seismicity were analyzed and compared with a similar anomaly which occurred on October 2016-May 2017. To better distinguish the seismotectonic anomalies from external geomagnetic variations (geomagnetic storms), the datasets recorded at Muntele Rosu (MLR) located inside seismogenic zone were compared with datasets recorded at Surlari (SUA) located at 100km away to the seismogenic area. Also, the geomagnetic data were correlated with the daily geomagnetic indices taken from NOAA/Space Prediction Center. During these two anomalies, were plotted graphs with daily and cumulative energy release for every earthquake bigger than Mw>3, occurring inside the anomalies. The anomaly which accompanied the moderate earthquake from October 28 th , 2018 is visible only on By component (EW component) of the local geomagnetic field and this anomaly is looking similar to the anomaly which occurred during October 2016-May 2017. Both of them shows a step-type change in By component and the total decrease measured on By component is around 100 nT. The computed seismic energy during the late geomagnetic anomaly showed low seismic activity in both magnitude and number. The unequal distribution of seismic energy during these two anomalies is explained by the depth occurrence of main shocks. During the anomaly occurred between October 2016 and May 2017, the seismic activity was greater and was concentrated in 90-100 km depth interval. Otherwise, during the recent anomaly, the seismic activity was lower and concentrated in 130-150 km depth interval. In the study of the relationship between geomagnetic anomalies and the occurrence of intermediate earthquakes is mandatory to take under consideration the depth interval where the earthquakes are concentrated. The mechanical response of intermediate depth structure could variate with the depth because the rheological properties of rocks are closely related to the changes in the pressure-temperature domain.

Authors:
Mihai A., Moldovan I. A., Toader V., Partheniu R., Petrescu L.

Abstract:
In this study were used geomagnetic data recorded during last 5 years, from 2013 till present. The records were corrected for missing and wrong data induced by malfunction of the data acquisition system. The main purpose of the paper is to identify the magnetic field behaviour in relation with space weather, meteorological phenomenon including annual/diurnal temperature variation, local and regional seismic activity. The paper is focusing on geomagnetic anomalies detected on the recorded field at one magnetometer located near Vrancea seismogenic zone prior to Mw>4.5 crustal and intermediate depth earthquakes. During these 5 years of investigations one crustal earthquake and three subcrustal earthquakes with a moment magnitude Mw between 5.0 and 6.0, occurred in the Vrancea zone. All three intermediate depth events were accompanied by significant anomalies on Y axis (EW component) of local geomagnetic field measured at MLR observatory. The MLR magnetometer was outside the preparation zone of the crustal earthquake, located at 100km distance from the epicenter, so no anomaly was observed. In order to highlight the anomalies recorded at Muntele Rosu (MLR) seismological observatory, these data were compared with data from Surlari (SUA) observatory, located about 150 Km South-East outside the Vrancea seismogenic zone. Similarly, earthquakes with Mw between 4.5 and 5 are accompanied by same type but smaller amplitude anomalies, were the drop on Y axis was less than 10 nT instead of 20-30 nT as those occurred prior to earthquakes with Mw>5.0. The latter ones are harder to observe during the summer time when these anomalies are hidden by large diurnal variations. The anomaly duration extends from days to sometimes months, without correlation with the earthquake magnitude. To better distinguish the local/regional anomalies from global geomagnetic behaviour, both MLR and SUA datasets were also corelated with the geomagnetic indices from NOAA/Space Prediction Center. The presence of geomagnetic storms creates a specific type of anomalies that sometimes might hide the ones related to earthquakes. The geomagnetic measurements were also compared with temperature values recorded at MLR station both for avoiding wrong interpretation of instrument response related to temperature variations, and to highlight possible correlations of magnetic field behaviour with ambient temperature. The three medium sized intermediate earthquakes that have occurred in the studied time interval provided a good opportunity to investigate the link between the presence of anomalies on geomagnetic records at Muntele Rosu observatory and seismicity in Vrancea zone.

Authors:
Moldovan I.A., Constantin A. P., Ardeleanu L., Ionescu C., Grecu B., Manea L. M., Toma-Dănilă D., Toader V.E., Partheniu R., Manea E. F., Tiganescu A., Placinta A. O.

Abstract:
Romania is one of the most seismic-prone countries in Europe due to the periodically occurrence of strong intermediate-depth earthquakes in Vrancea seismogenic zone. The Vrancea area is located beneath the South-Eastern Carpathian Arc bend, at the contact between the East - European plate and the Intra-Alpine and Moesian sub-plates. An intense seismic activity is recorded in the mantle, within a narrow, almost vertical descending volume between 60 and 180 km depth. Earthquakes with magnitudes larger than 5.0 (Mw) and macroseismic effects exceeding V MSK degrees on extended populated area occur in Vrancea seismic zone, with a return period of around 2 years. Besides the extended scientific studies, the near real time estimation of the macroseismic intensity recently became mandatory for the insurance companies to cover some of the losses and damages that earthquakes might cause to houses, belongings, and other buildings. The first approach to obtain intensity values was to develop an online environment for collecting people feedback regarding the effects of earthquakes and for the automatic approximation of the intensity. The automatic intensity estimation code from the online feedback proposed by [1], [2] and adopted by [3] for the Romanian earthquakes was improved and used for this study. Additionally, there were used prediction equations to obtain intensity values from the epicentral intensity, and epicentral and hypocentral distances. Besides the estimation of macroseismic intensities from online people feedback and from attenuation relations, equations for conversion of peak ground acceleration in macroseismic intensity were also required for a rapid evaluation of ground motion effects. In order to avoid the increase of the prediction uncertainties, the data must be selected in such a way that they represent the parameters’ rank for which the prediction will be accomplished and the selected data must be representative for the investigated regions and seismic source. In this paper were developed conversion methods from PGA to macroseismic intensity for moderate intermediate depths earthquakes with 4.5

Authors:
Moldovan I.A., Constantin A. P., Manea E. F., Partheniu R., Constantinescu E. G.

Abstract:
The macroseismic intensity attenuation and its variation as a function of the epicentral or hypocentral distance is one of the issues in the seismic hazard assessment and of shake map generation. This output is especially required by emergency situation inspectorates or by the insurance companies. The macroseismic intensity investigations are carried out in Romania after all earthquakes with magnitudes larger than 4.0. Starting with 2014 the classical method for macroseismic information collection was doubled by the online method, consisting in online questionnaires and rapid feedback based on pictograms. In the current study the ground-motion prediction equations were computed in terms of macroseismic intensity for Romania, using the large Mw>6.5 intermediate depth Vrancea earthquakes and were tested on the recent moderate events to certify their validity at lower ranges of magnitudes. The mathematical relation proposed by von Koveslighety in 1906 was used for analysing the attenuation of seismic intensity with distance in terms of the difference between the maximum observed intensity, referred here as epicentral intensity Io and site intensity I, for 24 different azimuths. The macroseismic catalogue used in the present study comprises 7461 intensity data points (IDP) for 5 large Vrancea (Romania) intermediate depth earthquakes (10th November 1940. 4th March 1977, 30th August 1986, 30th and 31st May 1990), 471 IDP?s for the moderate 27th October 2004 earthquake and 3048 IDP?s for nine intermediate depth moderate earthquakes (4.1

Authors:
Muntean A., Năstase E., Manea L.

Abstract:
Romania is covered by more than one hundred GNSS (Global Navigation Satellite System) permanent stations, that have been set up over the last seven years, maintained by different agencies and having different technical architectures and scientific objectives. Many of these stations provide support for geo-referencing applications such as surveying, the network being developed by National Agency for Cadaster and Land Registration (ANCPI) and by a private company, TopGeocart. Two networks are developed with scientific purposes: one developed by the National Institute for Earth Physics - NIEP and the other one developed by the National Institute for Research and Development on Marine Geology and Geo-ecology – GeoEcoMar. Several limiting factors were identified in terms of utilization: no site uniqueness, no file redundancy, no quality control or hardwire web service. Our goal is to collect all those GNSS data in order to standardize, perform quality control and harmonize for creating the metadata. We present and discuss step by step all the implementation levels of standard tools necessary for generating, validating and disseminating pre-defined GNSS metadata, tools for the generation and dissemination of metadata. All those will allow the end-users, and in particular, geoscientists, to freely access the geodetic data, derived solutions, and associated metadata using a transparent and standardized process. Finally, we detail the technologies and software that were used and developed to build this e-infrastructure, the system output data and the conclusions derived in terms of data volume, security and usefulness. The involvement in EPOS – IP project as a member of GNSS Data and Products Working Group helps us evolve in the same direction, test and implement GLASS software package for the dissemination of GNSS data & dedicated processing outcomes, time-series, velocities, and strain-rates - to be created using state-of-the-art methodologies for a better understanding and completion of the tectonic puzzle pieces of Solid Earth processes in this challenging structure of Southeastern Europe.

Authors:
Placintă A.O., Popescu E., Moldovan I.A., Radulian M., Mihai A.

Abstract:
The seismic hazard studies of the last 30 years have been largely carried out taking into account the needs of the construction engineers, by linking the specific quantities of soil movement with the physical parameters determined instrumentally, namely, with the maximum values of soil acceleration. At present, interest in the results of hazard studies has increased and has extended to other areas such as insurance or design companies, environmental protection, etc. A fundamental element in the estimation of seismic hazard is the variation of the amplitude of the movement of the soil according to the distance, magnitude and local conditions. To understand and prevent the effects of the strong Vrancea earthquakes in the dam sites located in the South West of Romania, we study the seismic waves attenuation relations using the accelerations recorded by the national network of K2 accelerometers, following the moderate Vrancea intermediate earthquakes. The study area includes the largest agglomeration of dams in Romania, with almost 100 dams out of the 250 large dams. One of the most important specific requirements towards dams' safety is the seismic risk and hazard assessment and the computation of attenuation relationships is one of the most important steps of the work. The main objective of the present work is the evaluation of the specific attenuation relationships of the seismic wave propagating from Vrancea subcrustal focus toward south-west, with direct application for the dams situated in the area.

Authors:
Dinescu R., Rogozea M., Popa M., Chircea A.

Abstract:
The most important products of the seismological network are complete and reliable earthquake catalogs. Detecting earthquakes over an extended scale, from smallest magnitudes to large events is a critical issue in many studies, such as earthquake statistics, source seismology and seismic hazard. During the last years, the seismic network of Romanian has developed by increasing the number of stations and station coverage. Despite the significant improvement, the coverage is still not uniform all over the Romanian territory due to some natural limits (geographical borders, topography, etc.). Because of this, the monitoring and localization of local seismic events with low-magnitude using routine detection and localization methods is sometimes difficult and may lead to considerable magnitude or location errors. Recorded data affected by errors and quarry blasts recorded as seismic events (earthquakes) in the Romanian earthquake catalogue (ROMPLUS) will distort the seismicity pattern characterizing a specific region. The goal of this study is to increase the capability to detect and localize low-magnitude seismic events in the south-eastern part of Romania (Dobrogea region) by applying the cross-correlation method for 2012 – 2016-time interval. To this aim, we selected six templates for events recorded both during working hours and during night. The waveform similarity analysis was performed on signals recorded on the vertical component of the seismic station Targusor (TIRR), a high-quality station operating in the study region. The waveforms recorded for template events are cross-correlated with successive windows from the continuous waveform recording along the entire time interval selected for our analysis. Window length and filtering parameters are properly adjusted in order to detect similarities among the waveforms of different events in connection with each template event. Finally, the detected events are investigated in order to discriminate tectonic events from man-made events following specific criteria: working hours, working days, monthly distribution, magnitude and depth of the event correlation with specific templates. The catalogue resulted from this work is analysed comparatively with the existing routine catalogue for Dobrogea.

Authors:
Mărmureanu G., Vacareanu R., Cioflan C.O., Ionescu C., Toma-Dănilă D.

Abstract:
The Vrancea seismogenic zone denotes a peculiar source of seismic hazard which represents a major concern in Europe, especially to Romania and neighbouring regions from Bulgaria, Serbia and Republic of Moldova. The strong seismic events that can occur in this area can generate the most destructive effects in Romania and may affect high-risk manmade structures such as nuclear power plants, chemical plants, large dams and pipelines located within a wide area including the Northern zone from the Republic of Bulgaria and the SW of the Moldavia Republic. A major part of the information for determining the design basis earthquakes consists of a complete set of historical earthquake data. Therefore, it is necessary that the available historical records to be collected, extending as far back in time as possible. Most of these historical records will be of descriptive nature, including such information as the number of houses damaged or destroyed, the behaviour of population etc. But from such information a measure of the intensity scale value of each earthquake in modern macroseismic intensity scale values may be determined. During the past project “Bridging the gap between seismology and earthquake engineering: from the seismicity of Romania towards a refined implementation of seismic action EN1998-1 in earthquake resistant design of buildings (BIGSEES)”, the authors developed the macroseismic intensity map of Romania by using newly compiled information about the damages experienced by 115 churches and monasteries after 10 strong earthquakes (Mw > 6.9) occurred in Vrancea zone starting with XVth century.

Authors:
Mihai A., Moldovan I-A., Toader V.E., Petrescu L, Partheniu R.

Abstract:
In this study were used geomagnetic data recorded during last 5 years, from 2013 till present. The records were corrected for missing and wrong data induced by malfunction of the data acquisition system. The main purpose of the paper is to identify the magnetic field behaviour in relation with space weather, meteorological phenomenon including annual/diurnal temperature variation, local and regional seismic activity. The paper is focusing on geomagnetic anomalies detected on the recorded field at one magnetometer located near Vrancea seismogenic zone prior to Mw>4.5 crustal and intermediate depth earthquakes. During these 5 years of investigations one crustal earthquake and three subcrustal earthquakes with a moment magnitude Mw between 5.0 and 6.0, occurred in the Vrancea zone. All three intermediate depth events were accompanied by significant anomalies on Y axis (EW component) of local geomagnetic field measured at MLR observatory. The MLR magnetometer was outside the preparation zone of the crustal earthquake, located at 100km distance from the epicenter, so no anomaly was observed. In order to highlight the anomalies recorded at Muntele Rosu (MLR) seismological observatory, these data were compared with data from Surlari (SUA) observatory, located about 150 Km South-East outside the Vrancea seismogenic zone. Similarly, earthquakes with Mw between 4.5 and 5 are accompanied by same type but smaller amplitude anomalies, were the drop on Y axis was less than 10 nT instead of 20-30 nT as those occurred prior to earthquakes with Mw>5.0. The latter ones are harder to observe during the summer time when these anomalies are hidden by large diurnal variations. The anomaly duration extends from days to sometimes months, without correlation with the earthquake magnitude. To better distinguish the local/regional anomalies from global geomagnetic behaviour, both MLR and SUA datasets were also corelated with the geomagnetic indices from NOAA/Space Prediction Center. The presence of geomagnetic storms creates a specific type of anomalies that sometimes might hide the ones related to earthquakes. The geomagnetic measurements were also compared with temperature values recorded at MLR station both for avoiding wrong interpretation of instrument response related to temperature variations, and to highlight possible correlations of magnetic field behaviour with ambient temperature. The three medium sized intermediate earthquakes that have occurred in the studied time interval provided a good opportunity to investigate the link between the presence of anomalies on geomagnetic records at Muntele Rosu observatory and seismicity in Vrancea zone.

Authors:
Moldovan I. A., Grecu B., Constantin A.P., Anghel A., Manea E.F., Manea L., Partheniu R.

Abstract:
In the last decade, many efforts were done to predict the macroseismic intensity in case of felt Vrancea earthquakes and additionally an online environment was developed for the automatic approximation of the intensity from peoples’ feedback. Besides the extended scientific studies, the near real-time estimation of the macroseismic intensity recently became mandatory for the insurance companies to cover some of the losses and damages that earthquakes might cause to houses, belongings, and other structures. Due to the insurance companies’ requests, the macroseismic questionnaires method was doubled by the seismic intensity determination using instrumental data, as recommended in the Romanian Seismic Intensity Scale Standard (STAS 3684-71). In the present study, the procedure is shown, for the last earthquakes with ML larger than 5.0, occurred in Vrancea zone, and felt on the extra-Carpathian area. We have selected the case study in Barlad, Vaslui county, because there have been recorded the largest accelerations (122 cm/s2) and have been reported the largest MSK intensities (VI) from Romania during the Mw 5.5 September 24, 2016 earthquake. The results obtained using the two approaches (macroseismic and instrumental data) have been compared and some differences have been found.

Authors:
Moldovan I.A., Manea L., Constantin A.P., Grecu B., Toma-Dănilă D.

Abstract:
Romania is one of the most seismic-prone countries in Europe due to the periodically occurrence of strong intermediate-depth earthquakes in Vrancea seismogenic zone. In the last decades, many efforts were done to gather macroseismic intensities in case of felt Vrancea earthquakes and additionally an online environment was developed for the automatic approximation of the intensity from people feedback. Besides the extended scientific studies, the near real time estimation of the macroseismic intensity recently became mandatory for the insurance companies to cover some of the losses and damage that earthquakes might cause to houses, belongings, and other buildings. The procedure proposed in this paper for rapid macroseismic estimation and loss assessment for the recent intermediate-depth Vrancea earthquakes with MW>4.5 is using the online macroseismic questionnaires, and the automatic intensity estimation code recently improved. Besides the automatic estimation, we have also used the classical approach to assess the intensity data points and also the available equations for conversion of peak ground acceleration in macroseismic intensity (including de Romanian Macroseismic Intensity Standard).

Authors:
Oros E., Moldovan I. A., Popa M., Diaconescu M., Ghiță C.

Abstract:
The paper presents a detailed analysis of the seismic activity recorded in the Banloc-Voiteg seismogenic structure (Romania) located on the southeastern border of the Pannonian Depression which is characterized by pre-Alpine and Alpine structures belonging to Tisa-Dacia Microplate and, particularly by the tectonic contact between two main geodynamic blocks. The seismic activity has a clear tendency to group on active neotectonic structures and displays different space and time patterns. Until now we have documented two major sequences (Imax=VIII EMS degree) in the study structure: October - November 1915 and July-December 1991. The 1991 sequence lasted several years, the seismic stations operated by NIEP recording thousands of aftershocks within several months. Some aftershocks had important macroseismic effects (e.g. 19.07.1991, Io=VII EMS). We refined hypocentral parameters for theis sequence using JHD relocation method. The new epicentres are well distributed in space and time defining two groups (phases) correlated with the faults systems in the study area. The focal mechanisms computed for the strongest events point out two orthogonal faults systems that were reactivated during the sequence, one oriented NE - SW (Banloc - Buzias Fault System) and the other one approximately E - W (Ittebej - Gataia Fault System) The seismic activity appears to migrate from South (Banloc phase, Mw=5.6, 12.07.1991) toward North (Voiteg phase, Mw=5.5, 02.12.1991) and further along Banloc - Buzias fault system.

Authors:
Ardeleanu L.

Abstract:
An inversion scheme using only few good quality high-frequency local waveforms was previously applied to estimate the source mechanism for a pilot set of crustal earthquakes with local magnitudes less than 4, from the bend of the South-eastern Carpathians. Taking advantage of the improved velocity and attenuation models recently determined for the study region, we reevaluate the focal mechanism of a couple of low-magnitude events (local magnitude ≥ 3), and assess the uncertainty of the fault plane solutions. The results evidence the increased reliability of the retrieved mechanisms and emphasize the capability of the approach to provide satisfactorily constrained fault plane solutions for the weak-to-moderate earthquakes in the study region.

Authors:
Ardeleanu L.

Abstract:
We investigate the shear wave attenuation in the crust beneath the area from the bending of the Eastern Carpathians by using a procedure based on highfrequency waveform modelling. We determine 1-D local models of the quality factor of the medium Q, adequate for simulating the ground motion (waveforms with maximum frequency 5 Hz) generated by seismic sources of Vrancea region at locations within the extra-Carpathian zone. The results of the study reveal distinct attenuative properties among the structural units lying in the study region; considerably higher attenuation is evidenced beneath the Focşani Basin and the Vrancea region orogen.

Authors:
Bala A., Tătaru D., Grecu B.

Abstract:
Tectonic of Romania includes both pre-alpine platforms and Alpine orogenic structures. The pre-alpine platforms are: Eastern European Platform, with its western margin in Romania—Moldavian platform; Scythian platform; Moesian platform.

Authors:
Oros E., Plăcintă A. O., Popa M.

Abstract:
The main task of the presented study is to elaborate a set of relations of mutual conversion macroseismic intensity - magnitude, necessary for the calibration of the historical crustal earthquakes produced in the Intra - Carpathian region of Romania, as a prerequisite for homogenization of the parametric catalogue of Romanian earthquakes. To achieve the goal, we selected a set of earthquakes for which we have quality macroseismic data and the Mw moment magnitude obtained instrumentally. These seismic events were used to determine the relations between the Mw and the peak/epicentral intensity, the isoseist surface area for I=3, I=4 and I=5: Mw = f (Imax / Io), Mw = f (Imax / Io, h), Mw = f (A3, A4; A5). We investigated several variants of such relationships and combinations, taking into account that the macroseismic data necessary for the re-evaluation of historical earthquakes in the investigated region are available in several forms. Thus, a number of investigations provided various information resulted after revising initial historical data: 1) Intensity data point (IDP) assimilated or not with the epicentre intensity after analysis of the correlation level with recent seismicity data and / or active tectonics / seismotectonics, 2) Sets of intensities obtained in several localities (IDPs) with variable values having maxims that can be considered equal to epicentral intensity (Io), 3) Sets of intensities obtained in several localities (IDPs) but without obvious maximum values, assimilable with the epicentral intensity, 4) maps with isoseismals, 5) Information on the areas in which the investigated earthquake was felt or the area of perceptiveness (e.g. I = 3 EMS during the day and I = 4 EMS at night) or the surfaces corresponding to a certain degree of well-defined intensity. The obtained relationships were validated using a set of earthquakes with instrumental source parameters (localization, depth, Mw). These relationships lead to redundant results meaningful in the process of estimating the quality and credibility of the primary data used (e.g. IDPs, isoseismals) and in the correct determination of Mw.

Authors:
Chalyi O., Diaconescu M., Gurova I., Lisovyi Y., Pigylevsky P., Shcherbina S., Shevtsov A., Shumlianska L.

Abstract:

Authors:
Cioflan C.O., Radulian M., Ionescu C. Bălan S.F., Apostol B.F.

Abstract:
The paper goal is to discuss some aspects regarding the influence of the dominant periods of the soil layers and fundamental periods of the built structure, starting from earthquakes records and using already known data about the oscillation period of the subsoil. We will focus our analysis on Bucharest Metropolis foundation soils, where buildings are placed in an area exposed to high seismic hazard. The regions of the south-east and south of Romania are affected mainly by the Vrancea strong earthquakes, generated at the South-Eastern Carpathians Arc bend at intermediate depth. In the XXth century four major earthquakes (Mw > 7) were reported. The methods used for computing the oscillation period of the soil are reviewed. By knowing the dominant periods over the Bucharest area, we can appreciate if a building is suitable or not for a specific site. In the authors’ opinion, it is safer to pick the right structure to be build up in a given area than to force a non-resonance design in that place. Consequently, some seismic risk considerations from soil-foundation-structure interaction perspective will be presented. This will have to be a very effective way of getting the right answers when trying to build a special construction on a site.

Authors:
Craiu A., Ghiță C., Craiu M., Diaconescu M., Mihai M., Ardeleanu L.

Abstract:
The moderate-size earthquake (local magnitude 5.7) which occurred on November 22, 2014 in Vrancea region (Romania), is the largest crustal event instrumentally recorded. Its aftershock sequence lasted around 70 days, 222 earthquakes with local magnitude ≥ 0.1 being located using the records collected by the Romanian seismic network. The seismic sequence occurred mainly in the lower crust (depths greater than 25 km), and the epicenter distribution – along a NNE-SSW direction followed the orientation of the Vrancea crustal earthquakes alignment. The sequence, occurred in the Focsani Basin (part of the Moesian Platform) and is related to the normal fault system associated to the major Peceneaga - Camena fault, which separates the Moesian Platform from the North Dobrogea promontory. The spatio-temporal distribution of the seismic activity, as well as the seismic energy released during the seismic sequence are analysed in detail, and the focal mechanisms of the largest events – 34 shocks with ML ≥ 1.8 – are determined using reliable P-wave polarities and amplitude ratios. Taking into consideration that the moderate-size shock of November 22, 2014 is the strongest instrumentally recorded crustal earthquake in the region, its focal mechanism provides highly relevant seismological information on the deformation field in front of the Carpathian bend. The obtained fault plane solution indicates normal faulting with a dominant dip-slip component; both nodal planes being oriented NW-SE.

Authors:
Grecu B., Neagoe C., Tătaru D., Zaharia B., Borleanu F.

Abstract:
We present the first detailed investigation of the background seismic noise recorded in the Romanian-Bulgarian cross-border region over 3 years (2012–2015). We used the power spectral densities probability density functions (PSD PDFs) to study the noise variations in the period domain (0.025–1 s) as well as in the secondary microseism band (2–10 s). Strong diurnal variations and an increase of the noise levels during working days were observed at high frequencies at all stations, thus confirming the anthropic origin of the noise at low periods. The noise variations observed at longer periods (> 1 s) are relatively small among the stations and are related to season changes. The dominant feature in the noise spectra between 2 and 10 s is the double-frequency peak (DFP) whose amplitude increases and changes during winter. For a specific interval, from 25th to 27th of January 2014, when a storm was reported in the Black Sea area, the maximum of the DFP shifted from larger periods (~ 5.5 s) at stations far from the Black Sea towards smaller periods (~ 1.8 s) at stations located on the coastline. The polarization analysis showed that the short period double-frequency microseisms originating from the Black Sea dominate during the winter month. Finally, we showed that site conditions vary due to noise variations related to weather conditions in the Black Sea or to changes in anthropogenic noise sources.

Authors:
Grecu B., Zaharia B., Diaconescu M., Bala A., Nastase E., Constantinescu E., Tătaru D.

Abstract:
Strong motion data are essential for seismic hazard assessment. To correctly understand and use this kind of data is necessary to have a good knowledge of local site conditions. Romania has one of the largest strong motion networks in Europe with 134 real-time stations. In this work, we aim to do a comprehensive site characterization for eight of these stations located in the eastern part of Romania. We make use of a various seismological dataset and we perform ambient noise and earthquake-based investigations to estimate the background noise level, the resonance frequencies and amplification of each site. We also derive the Vs30 parameter from the surface shear-wave velocity profiles obtained through the inversion of the Rayleigh waves recorded in active seismic measurements. Our analyses indicate similar results for seven stations: high noise levels for frequencies larger than 1 Hz, well defined fundamental resonance at low frequencies (0.15–0.29 Hz), moderate amplification levels (up to 4 units) for frequencies between 0.15 and 5–7 Hz and same soil class (type C) according to the estimated Vs30 and Eurocode 8. In contrast, the eighth station for which the soil class is evaluated of type B exhibits a very good noise level for a wide range of frequencies (0.01–20 Hz), a broader fundamental resonance at high frequencies (~ 8 Hz) and a flat amplification curve between 0.1 and 3–4 Hz.

Authors:
Guéguen P., Țigănescu A.

Abstract:
The real-time analysis of a structure’s integrity associated with a process to estimate damage levels improves the safety of people and assets and reduces the economic losses associated with interrupted production or operation of the structure. The appearance of damage in a building changes its dynamic response (frequency, damping, and/or modal shape), and one of the most effective methods for the continuous assessment of integrity is based on the use of ambient vibrations. However, although resonance frequency can be used as an indicator of change, misinterpretation is possible since frequency is affected not only by the occurrence of damage but also by certain operating conditions and particularly certain atmospheric conditions. In this study, after analyzing the correlation of resonance frequency values with temperature for one building, we use the data mining method called “association rule learning” (ARL) to predict future frequencies according to temperature measurements. We then propose an anomaly interpretation strategy using the “traffic light” method.

Authors:
Pilger C., Ceranna L., Ross J.O., Vergoz, J., Le Pichon A., Brachet N., Blanc E., Kero J., Liszka L., Gibbons S., Kvaerna T., Näsholm S. P., Smets P., Evers L., Marchetti E., Ripepe M., Sindelarova T., Lastovicka L., Ghica D., Ionescu C., Ben Horin Y., Mialle P..

Abstract:
The European Infrasound Bulletin highlights infrasound activity produced mostly by anthropogenic sources, recorded all over Europe and collected in the course of the ARISE and ARISE2 projects (Atmospheric dynamics Research InfraStructure in Europe). Data includes high-frequency (> 0.7 Hz) infrasound detections at 24 European infrasound arrays from nine different national institutions complemented with infrasound stations of the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Data were acquired during 16 years of operation (from 2000 to 2015) and processed to identify and locate ∼ 48,000 infrasound events within Europe. The source locations of these events were derived by combining at least two corresponding station detections per event. Comparisons with ground-truth sources, e.g., Scandinavian mining activity, are provided as well as comparisons with the CTBT Late Event Bulletin (LEB). Relocation is performed using ray-tracing methods to estimate celerity and back-azimuth corrections for source location based on meteorological wind and temperature values for each event derived from European Centre for Medium-range Weather Forecast (ECMWF) data. This study focuses on the analysis of repeating, man-made infrasound events (e.g., mining blasts and supersonic flights) and on the seasonal, weekly and diurnal variation of the infrasonic activity of sources in Europe. Drawing comparisons to previous studies shows that improvements in terms of detection, association and location are made within this study due to increasing the station density and thus the number of events and determined source regions. This improves the capability of the infrasound station network in Europe to more comprehensively estimate the activity of anthropogenic infrasound sources in Europe.

Authors:
Poiata N., J.P., Vilotte P., Bernard C., Satriano C., Obara K.

Abstract:
In this study, we demonstrate the capability of an automatic network-based detection and location method to extract and analyse different components of tectonic tremor activity by analysing a 9-day energetic tectonic tremor sequence occurring at the downdip extension of the subducting slab in southwestern Japan. The applied method exploits the coherency of multiscale, frequency-selective characteristics of non-stationary signals recorded across the seismic network. Use of different characteristic functions, in the signal processing step of the method, allows to extract and locate the sources of short-duration impulsive signal transients associated with low-frequency earthquakes and of longer-duration energy transients during the tectonic tremor sequence. Frequency-dependent characteristic functions, based on higher-order statistics’ properties of the seismic signals, are used for the detection and location of low-frequency earthquakes. This allows extracting a more complete (∼6.5 times more events) and time-resolved catalogue of low-frequency earthquakes than the routine catalogue provided by the Japan Meteorological Agency. As such, this catalogue allows resolving the space–time evolution of the low-frequency earthquakes activity in great detail, unravelling spatial and temporal clustering, modulation in response to tide, and different scales of space–time migration patterns. In the second part of the study, the detection and source location of longer-duration signal energy transients within the tectonic tremor sequence is performed using characteristic functions built from smoothed frequency-dependent energy envelopes. This leads to a catalogue of longer-duration energy sources during the tectonic tremor sequence, characterized by their durations and 3-D spatial likelihood maps of the energy-release source regions. The summary 3-D likelihood map for the 9-day tectonic tremor sequence, built from this catalogue, exhibits an along-strike spatial segmentation of the long-duration energy-release regions, matching the large-scale clustering features evidenced from the low-frequency earthquake's activity analysis. Further examination of the two catalogues showed that the extracted short-duration low-frequency earthquakes activity coincides in space, within about 10–15 km distance, with the longer-duration energy sources during the tectonic tremor sequence. This observation provides a potential constraint on the size of the longer-duration energy-radiating source region in relation with the clustering of low-frequency earthquakes activity during the analysed tectonic tremor sequence. We show that advanced statistical network-based methods offer new capabilities for automatic high-resolution detection, location and monitoring of different scale-components of tectonic tremor activity, enriching existing slow earthquakes catalogues. Systematic application of such methods to large continuous data sets will allow imaging the slow transient seismic energy-release activity at higher resolution, and therefore, provide new insights into the underlying multiscale mechanisms of slow earthquakes generation.

Authors:
Popa, M., Munteanu I., Borleanu F., Oros E., Radulian M., Dinu C.

Abstract:
Active tectonic deformation is continuously shaping the landscape in the Alpine Orogenic system. Earthquakes are clear proves of neotectonic deformation process. In the Romanian Carpathians the most active deformation is recorded in the South Eastern Carpathian Bend Zone. Nevertheless, seismicity associated to latest orogenic stage of active deformation is not limited to this area. Other seismic regions, like the South West Carpathians Bend Zone, were identified. Recently, several earthquake sequences were recorded in the Caransebes-Mehadia (CMB) and Hateg basins (HB). These sedimentary basins developed over the South Carpathians, Getic/Supra Getic and Danubian basement napes, their evolution being related with the N-ward tectonic transport of the Carpathian Orogen, in the current position, during the Paleogene-Quaternary times. The aim of the present study is to perform a thorough analysis of the earthquakes recorded in these two basins in correlation with the observed geological structure to better understand and constrain the neotectonic processes affecting the SW Carpathians Bend Zone. The focal mechanisms determined for HB show a predominant strike-slip faulting component with the principal axes oriented approximately NW–SE (compression) and NE–SW (extension), a reorientation from the N-S one described for the Pliocene–Pleistocene phase. The focal mechanisms in CMB imply N–S extension with normal or strike-slip faulting. We argue that the present day tectonic processes are not restricted to the SE Carpathians Bend zone, as previously inferred. Instead they affect a much larger area of the Carpathian Orogen, like the SW Carpathians Bend zone.

Authors:
Popescu E., Radulian M., Bala A., Toma-Dănilă D.

Abstract:
Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998-2012 time interval. The catalogue is limited geographically to the Carpathians Orogeny and extra-Carpathians area located in the southeastern part of Romania because similar investigations cover the rest of the country. The catalogue comprises 259 intermediate-depth seismic events and 90 crustal seismic events, recorded in the considered time interval with acceptably constrained fault plane solutions. We use specific graphical tools in order to emphasize statistically representative features of the stress field as coming out from our results. The fault plane solutions of the Vrancea earthquakes generated in a confined sinking plate in the mantle reflect the dominant geodynamic process in the study region. The typical features revealed by all the previous studies on the subcrustal seismic activity (predominant dip-slip, reverse faulting, characterizing both the weak and strong earthquakes) are reproduced as well by our investigation. As concerns the earthquake activity in the crust, a few new refined aspects are highlighted in the present work: (1) a deficit of the strike-slip component over the entire Carpathians foredeep area, (2) different stress field pattern in the Făgăraş-Câmpulung zone as compared with the Moesian Platform and Pre-Dobrogean and Bârlad Depressions, (3) a larger range for the dip angle of the nodal planes in the Vrancea subcrustal source, ~ 40 0-70 0 against ~ 70 0 , as commonly considered.