SEISMICITY of the CARPATHIANS in 2015

The article describes seismic observations in the Carpathian region in 2015, which were carried out, as before, by two organizations from two states: in Ukraine – the Seismicity department of the Carpathian region of the Institute of Geophysics of the NAS of Ukraine, in Moldova – the Seismology laboratory of the Institute of Geology and Seismology of the Academy of Sciences of Moldova. 20 stationary digital stations with a processing center in L'viv and six stations with a center in Chisinau operated in Ukraine and Moldova respectively. Different programs, local hodographs and magnitudes were used. The consolidated catalogue of earthquakes was created in L'viv. The total number of earthquakes in 2015 was NΣ=164 in the ranges: KR=4.7–12.2, h=1–160 km. The total seismic energy ΣE=5.381012 J. 23 earthquakes with depths h=50–160 km were located in the Vrancea zone. The maximum earthquake with KR=12.2 was registered on January 24 in the Vrancha mountains with hрР=89 km. In the Precarpathian region, nine events with energy classes KR=4.7–8.9 were registered, the total seismic energy of which is ΣЕ=1.25109 J. Increased seismic activity was observed in Transcarpathia. A series of tangible earthquakes with aftershocks was recorded in the Tyachiv area. Their total number was NΣ=77. The strongest tangible earthquake occurred in the area of Okrugla village on July 19 with KR=11.1. The earthquake source is located in the Earth's crust at a depth of h=7.7 km. The earthquake was felt by the population in the epicentral area with an intensity of I=6. In addition, this earthquake, like 5 others, was felt in the territory of northern Romania. In general, a decrease in the seismicity level in the Carpathians in 2015 was observed compared to that in 2013 and 2014.

Analysis of the possibility for seismic early warning in the Balkan Peninsula

This study analyses the possibility for seismic early warning (EW) in the Balkan Peninsula. A number of characteristics of seismic record were evaluated for EW utility. Some tests checked the possibility to locate events reliably by Golitsyn’s method, using one seismic station (SS). The distance and relevant travel time from some crustal faults to the nearest SS and big towns were appraised. EW procedures for most of the seismic zones in the Balkan Peninsula are not reliable, excepting the Vrancea zone, because of the small density of the SS, crustal depth of the earthquakes and fault crowdedness of the region.

Analysis of Exponent K Based on “Share” Project Data and Its Implications on Importance Factors of En 1998-1

This paper deals with seismic activity represented by a hazard curve through a single parameter – exponent k as given in EN 1998-1, as well as with its implications on importance factors. We have used the SHARE project dataset for calculation of exponent k for the wider European area and limited number of separate national studies for comparison of results since comparison to the SHARE results on the same dataset resulted with values of exponent k smaller by 1–1.5. The results indicate that recommended value of exponent k of 3 is rather an exception than expected value in seismically active regions, and that with the exclusion of Vrancea zone, for majority of Europe exponent k is well below assumed in EN 1998-1, which consequently indicate that importance factors for these locations should be larger than recommended in EN 1998-1.

The geomagnetic field behavior inside Vrancea zone (Romania) in correlation with tectonic, atmospheric and solar activity

<p>The present study assesses two signal processing methods on geomagnetic data to detect precursory signals appearing before M>5.0 Vrancea, Romania earthquakes occurred between 2016 and 2021. Geomagnetic data are obtained from Muntele Rosu Seismological Observatory situated in one corner of Vrancea seismogenic zone – as primary station, and from Intermagnet Surlari National Geomagnetic Observatory of IGR, located about 150Km South-East to Vrancea zone as remote station respectively. The first method, the diurnal variation ratio method computes difference between daily maximum with minimum value before finding ratio of primary to remote station for each individual component. The second method, the polarization ratio analysis is performed on both stations data to compute the ratio of vertical to total horizontal component in ultra-low frequency range. Geomagnetic indices taken from NOAA/Space Weather Prediction Center are compared to separate the global variation from seismo-electromagnetic anomalies possibly presented in a seismic area like Vrancea zone and to ensure that any geomagnetic fluctuations are not caused by solar-terrestrial effect.</p><p>In the end, the paper aims to compare the results from both methods in term of reliability and effectiveness.</p><p>Acknowledgements. This work was funded by: PN19 08 01 01/2019 Multirisc Nucleu Project, by MCI , Phenomenal Project PN-III-P2-2.1-PED-2019-1693, 480PED/2020 and AFROS Project PN-III-P4-ID-PCE-2020-1361, PCE/2021 supported by UEFISCDI</p>

Cluster analysis in the studying of stress relation in the Vrancea-zone

<p>The SE-Carpathians produce significant geodynamic activity due to the current subduction process. The strong seismicity in the Vrancea-zone is its most important indicator. The focus area of these seismic events is relatively small, around 80*100 km and the distribution of their locations is quiet dense.</p><p>The authors have carried out cluster analyses of the focal mechanism solutions estimated from local and tele-seismic measurements and stress inversions to support the recent and previously published studies in this region. They have applied different pre-existing clustering methods – e.g. HDBSCAN (hierarchical density-based clustering for applications with noise) and agglomerative hierarchical analysis – considering to the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the used seismic events, as well. Moreover, they have attempted to improve a fully-automated algorithm for the classification of the earthquakes for the estimations. This algorithm does not call for the setting of hyper-parameters, thus the affection of the subjectivity can be reduced significantly and the running time can be also decreased. In all cases, the resulted stress tensors are in close agreement with the earlier presented results.</p>

CARPATHIANS

The article describes seismic observations in the Carpathian region in 2014, which were carried out, as before, by two organizations from two states: in Ukraine – the Seismicity Department of the Carpathian region of the Institute of Geophysics of the National Academy of Sciences of Ukraine, in Moldova – the Seismology Laboratory of the Institute of Geology and Seismology of the Academy of Sciences of Moldova. In Ukraine, 20 stationary digital stations and 3 temporary ones worked in the Dniester energy complex with a processing center in Lviv, in Moldova - six stations with a center in Chisinau. Different programs, local hodo-graphs and magnitudes were used. The consolidated catalog of earthquakes was created in Lviv. A map of epi-centers and a table of the distribution of earthquakes of different classes by region are given. The total number of earthquakes in 2014 was NΣ=81 in the range KP =5.2–14.3 with the interval of hypocenter depths h=1–154 km and the total seismic energy ΣE=2.11·1014 J. Of these, 18 earthquakes with depths h=77–154 km located in the Vrancea zone. The maximum earthquake with KP=14.3 was registered on November 22 in the Precarpathian Trough with hрР=37 km. In the Vrancha mountains the maximum earthquake occurred on March 29 with the KP=12.5 and hрР=136 km. In the Precarpathian and Transcarpathian regions, all earthquakes were weaker. The most powerful event in Transcarpathia was a perceptible earthquake that occurred near the Trostnyk seismic station on November 15 with KP=8.9. The earthquake source is located in the Earth's crust at a depth of h=10 km. The earthquake was felt by the population of the Dyakovo, Trostnyk, Fanchykovo villages with the intensity of 5 and 4–5. In general, in all the seismically active zones of the Carpathians in 2014, there was a slight increase in the level of seismicity compared to that in 2013.

On In-Situ Disposal of ChNPP Facilities

The paper considers the possibility of applying in-situ disposal practice for Chornobyl exclusion zone facilities, in particular: ChNPP-1-3 that are under decommissioning, Shelter, RWDS ChNPP Stage III and RWDS Pidlisny. It was concluded that these facilities would not reach safety level over the next 300 years sufficient for clearance from regulatory control. In-situ disposal of ChNPP-1-3 would lead to a potential hazard related to a large amount of irradiated reactor graphite. Artificial barriers of concrete and bulk clay will not provide isolation of radionuclides, primarily radiocarbon, from the environment. The paper considers possible natural factors, the effect of which for the time required for the decay of radionuclides to acceptable level, can lead to destruction of surface storage facilities on ChNPP site. Such factors are as follows: probable transformation of Pripyat river valley; seismic influence related to both strong earthquakes in the Vrancea Zone (Romania) and the influence of local seismic centre. It raises issues connected with considering climate change, duration of and change in climate cycles for safety justification of in-situ disposal practices for ChNPP facilities. It was concluded that at this time it is impossible, to prove safety of surface burial on ChNPP site for the period of tens of thousands of years, since a number of external factors have probabilistic nature.

Towards understanding the roll-back subduction of narrow oceanic domains: inferences from the modelling of Carpathians subduction zone

<p>Numerous subduction systems in the Meditteranean realm are derived from the subduction of narrow oceanic domains, which are too narrow to generate the means of a fully coupled two-dimensional thermo-mechanical numerical model that takes into account the visco-elasto-plastic properties of different lithospheric domains. The results show that the narrow extent of the Ceahlau-Severin Ocean commonly assumed by paleogeographic reconstruction cannot generate roll-back upon subduction, in particular for models that must assume that slabs do not penetrate the 660 km discontinuity. Therefore, we propose that the subduction of the Carpathians system must have an inherited component from a previous orogenic evolution, which will ensure sufficient slab-pull to generate roll-back in the Carpathians realm. The model is constrained by recent results in terms of mantle structure and geodynamic reconstructions, while multiple compositional, thermal distribution and geometrical scenarios are tested in successive models. In all of our models, roll-back is achieved, which indicates that the proposed inherited component can sufficiently explain the roll-back subduction of the aforementioned narrow oceans. The subducting oceanic slab does not penetrate the 660 km discontinuity, this is in agreement with seismic tomographic results from various Mediterranean subduction zones. The exact onset and dynamics of the roll-back are mostly controlled by the thermic age of the ocean and the convergence kinematics of the continental slabs. An outlook on possible future improvements to the model, such as taking into account pre-existing rheological weakness zones in the lithosphere, is discussed and the opportunity of a seismo-thermo-mechanical modelling to investigate the seismic cycle in the Vrancea-zone is highlighted.</p>

On the anisotropy of seismic waves in the Carpathian region

The anisotropy of seismic waves in the continental regions still belongs to the category of controversial issues, since its estimates in different areas show a different sign of the anisotropy coefficient. In contrast to studies of oceanic regions, where SH velocities always prevail over SV velocities, in the continental regions the relations between the velocities are very different. The explanation for this, first of all, is the difference in structure. The structure of the crust and upper mantle under the oceans is much more homogeneous in comparison with the structure of the continental regions. There are several approaches to the estimation of anisotropy. The most traditional method is to use the maximum amount of data separately for Love and Rayleigh waves to study the lateral distributions of SH- and SV-wave velocity, despite the fact that the density of the coverage by paths, and, consequently, the regions of best resolution can be of different shapes and sizes. It was decided to use this method as the first approximation in creating an anisotropic portrait of the Carpathian region. The Carpathian region was chosen as the object of study, since it contains interesting contrasting features: (1) the Pannonian Basin, which is characterized by a thin crust, a thinned lithosphere, and anomalously high values of the heat flux; (2) the Tornquist-Teisseyre zone, which is parallel to the strike of the Eastern Carpathians, and represents the contact zone of the Precambrian lithosphere of the EEP and the relatively young lithosphere of Western Europe. (3) The third feature is the Vrancea zone, one of the most active seismic zones in Europe. It is located in the junction of young tectonic structures: the Southern and Eastern Carpathians, the Transylvanian Depression and the Pre-Carpathian Depression. The results of the study confirm that the Tornquist-Teisseyre Zone divides the structures of the ancient East European Platform and orogenic zones of Western Europe: the upper mantle throughout EEP is characterized by high velocities, whereas velocities throughout WE are markedly lower. Low velocity anomalies prevail under Pannonian Basin which is characterized by anomalously high heat flow values. The distribution of the anisotropy coefficient demonstrates an extended layer of low values of the anisotropy coefficient at depths of 150-200 km. Above this layer, velocity distributions reveal the block structure of the lithosphere. The earthquake sources in the Vrancea zone fall into the transition zone from the highvelocity mantle under the EEP to the low-velocity mantle under the WE. Earthquakes do not occur below the revealed asthenospheric layer.