Geodynamic Situation Research Articles

Hydroisostasy in the Far Eastern seas of Russia and its influence on the current sea level and geodynamic situation

Changes in the water surface level in the World Ocean and seas directly, and most often negatively, aff ct economic activity in coastal areas. After the completion of the last glacial maximum, ocean transgression due to the fl w of meltwater from glaciers at a rate of tens of millimeters per year practically stopped 4 thousand years ago. However, with the beginning of the technogenic era, due to the acceleration of further degradation of ice sheets, the rise in sea level, which is estimated at a few millimeters per year, resumed. However, there is still a contribution to the change in modern sea level from the residual effects of post-glacial transgression. The article examines one of the most significant residual effects influencing the current change in the water level of the World Ocean and manifesting itself in regions remote from the centers of glaciation - the effect of hydroisostasy. Hydroisostasy is a change in the load on the earth’s surface and the response of the earth’s surface as a result of an increase or decrease in the depth of the water layer in reservoirs (lakes, seas, oceans) after the melting or growth of glaciers. Significant consequences of hydroisostasy, in addition to the contribution to the reshaping of the structure of coastal areas, also appear to be a contribution to modern geodynamics.

АНАЛИЗ ГЕОЛОГИЧЕСКИХ И ИНЖЕНЕРНО-ГЕОЛОГИЧЕСКИХ УСЛОВИЙ ОСОБО ОХРАНЯЕМОЙ ПРИРОДНОЙ ТЕРРИТОРИИ - ИЛЬМЕНСКИЙ ГЛИНТ

lmensky Klint” on the territory of the Southern Ilmen region is a complex extended natural monument of regional importance, an ornithological monument of international importance. This valuable geological object is actively being destroyed and requires the close attention of many specialists. The article shows that despite the good accessibility of research objects and the existing scientific research on various topics, no emphasis was placed on studying the geodynamic situation of a specially protected natural area — the Ilmensky Klint. A brief qualitative assessment of the condition of the Ilmensky Klint is given based on the results of reconnaissance observations. A set of available measures is recommended to save this unique geological object in the north-west of Russia

Geodynamic issues of ore deposits in Central Asia

The focus of this study is on a pressing issue in ore geology, specifically the geodynamics of ore formation. The paper delineates a comprehensive methodology for examining the geodynamic context in regions hosting endogenous mineralization. The foundation for reconstructing geodynamics lies in geological and structural investigations into the circumstances surrounding mineralization, complemented by outcomes from physical modeling. Tectonic tension and deformation analyses of ore fields and deposits further contribute crucial insights. The study underscores that understanding the geodynamic setting is paramount for elucidating the processes leading to ore formation. This involves a detailed examination of geological structures, conditions of mineralization, and physical modeling results. By adopting this approach, the research provides a robust framework for reconstructing the geodynamic conditions prevalent during the period of ore formation. As a practical application of this methodology, the paper presents results from the reconstruction of the geodynamic situation during the ore formation period in a gold deposit situated in Western Uzbekistan. These findings contribute to a deeper comprehension of the geodynamic processes associated with the formation of valuable mineral deposits, thereby enhancing our ability to interpret and potentially predict similar occurrences in ore geology.

Zhaman-Koitass granite-leukogranite massif (Northern Kazakhstan): U-Pb age, mineralogical and geochemical features, geodynamic analysis

Research subject. The Zhaman-Koitass granite-leucogranite massif of the Borovsk complex in Northern Kazakhstan. In the platform cover of the West Siberian plate, overlying granite-leucogranites, a large uranium deposit Semizbai of sandstone type is localized. Materials and methods. Geochemical, mineralogical, and geochronological studies of granite-leucogranites were conducted by X-ray fluorescence analysis, ICP-MS, electron probe microanalysis, scanning electron microscopy, and LA-ICP-MS (Analytical Center for multi-elemental and isotope research SB RAS). Results and conclusions. The Zhaman-Koitass massif is composed by A-type subalkaline leucogranites (SiO2 = 72.8–75.4 wt %, Na2O + K2O = 7.5–8.8 wt %, K2O/Na2O = 1.11–1.25, ∑REE = 120–231 ppm, (La/Yb)n = 10–22, Eu/Eu* = 0.2–0.4), which are characterized by titanite-ilmenite-magnetite accessory specialization. U-Pb isotope dating confirms the silurian age of the Zhaman-Koitass granite-leucogranites (426–420 Ma). The obtained geochronological data, along with the similarity of the chemical composition of the rocks, confirm that the granite-leucogranites of the Zhaman-Koitass massif belong to the Borovsk complex. The significant age interval between the ordovician granitoids of the krykkuduk complex (448 ± 2 Ma) and the silurian granite-leucogranites of the karabulak and borovsk complexes considered in the article (431–426 Ma) suggests a change in the geodynamic situation from suprasubduction to transform marginal-continental.

On the influence of the supposed global deep fault on the strong earthquakes in Indonesia

According to the NEIC global catalog, out of 14 earthquakes with a magnitude of MS ≥7.0 registered in the world in the first six months of 2023, two belong to the powerful multi-earthquake of Turkey 06.02.2023 (Mw: 7.8 и 7.7), and the remaining 12 occurred in the Indonesian region. In the paper the geodynamic situation in the preparation of a series of Indonesian events, which began with two earthquakes: 08 and 09.01.2023 (MS : 7.0 и 7.6, Н=29 и 105 km), is investigated by means of a geoinformation system by means of a geoformation system GIS-ENDDB. It is established that all 12 earthquakes are spatially confined to the sub-latitudinal “Indonesian” seismolineament with a length of 9500 km, detected by the method of the great circle of the Earth. The dynamics of changes in the geophysical environment properties of the 950-kilometer zone from the axis of the lineament was estimated by the value of the paired correlation of magnitude MS and creepex Cr0_ISC. Two methods were used to calculate the coefficient of paired correlation of these parameters in a sliding time window: 1) with a fixed window size and 2) with one edge fixed at zero time (corresponding to the moment of the strongest Indonesian event on 09.01.2023). Both methods confirm the fact of monotonous consolidation of the environment along the lineament (evenly along its entire length and depth) 33 days before and 31 days after the strongest Indonesian shock: at the interval of reverse correlation (|KKOR|≥0.7) of magnitude and creepex. The same pattern was previously described by us for the consolidated part of the earth’s crust, where stronger earthquakes have a smaller creepex (characterizing the greater contribution of brittle destruction). Thus, the fact of the formation of an organized state of the environment (linear rigid structure) within the limits of the assumed deep fault, affecting the subsequent seismicity of the region in the form of a spatially timed semi-annual series of the strongest earthquakes with MS ≥7.0 is confirmed.

Разломная тектоника Ухтинской складки Тиманской гряды

he article deals with a model of the fault tectonics of the Ukhta fold in the Timan Ridge, created on the basis of reinterpretation of seismic data. By the results of constructions along the top of the Upper Proterozoic basement, the majority of the faults have a northwestern direction and extend both continuously and fragmentarily throughout the entire structure. Only north-west-directed faults are clearly traced over the surface of the Devonian deposits. The overlay of the obtained scheme onto the map of the anomalous magnetic field indicates that the identified faults are normally missed in the magnetic field when surveying at a scale of 1:50 000. For the detail site location of the faults and the continuous research of the geodynamic situation, a complex of field geophysical works is required to be conducted in the future.

Geochemistry of Xenoliths in Rapakivi Granites of the Korsun-Novomyrhorod Pluton (Ukrainian Shield)

Rapakivi of the Korsun-Novomyrhorod pluton (KNP), being the latest Precambrian granites of the central part of the Ukrainian shield, contain older acidic and intermediate rocks as xenoliths, the geochemical features of which reflect the Early Proterozoic geodynamic situation. Rapakivi granites, their differentiates and three types of xenoliths in them, represented by plagiogneiss, pink granite and charnockitoid (mangerite), were selected in the northwestern part of the KNP for geochemical studies. Analysis findings were compared with the geochemical characteristics of similar rocks of igneous and metamorphic Precambrian complexes that surround the KNP and could serve as a source of xenoliths. Based on distribution patterns of rare earth elements, lithophile elements content and their ratios relations in the rocks, taking into account their petrographic composition, it was established that plagiogneiss belongs to the upper part of the Inhul-Inhulets series, pink granite belongs to the Kirovohrad complex, and charnokitoid belongs to the intermediate rocks of the Tashlyk complex. In the latter, acid charnockitoids (enderbites) are probably younger than intermediate ones and were formed in another geodynamic setting. Pink granite, like the granites of the Kirovohrad complex, shows collisional geochemical features, in contrast to the rapakivi granites containing these xenoliths, which have predominantly within-plate geochemical characteristics. Thus, in the form of xenoliths in rapakivi those rocks were preserved that had been generated before and during the collision that occurred about 2 billion years ago and constructed a crust thickening at the site of the Inhul megablock, under subsequent extension of which about 1.75 billion years ago the KNP was intruded. Acid charnockitoids of the Tashlyk complex and rocks of the Novoukrainian complex, which are absent in xenoliths, probably were formed after the collision.

Петрогеохимия гранитов Бадьяюского массива (Приполярный Урал)

Magmatic formations of various ages are developed within the northern part of the Circumpolar Urals, the oldest peripheral part of the Ural belt. Including the Late-Riphean-Vendian granitoids of the salner-mankhambov intrusive complex, which includes the Badiayu granite massif. The conducted research allowed us to identify a number of petrographic and petrogeochemical features of the granites under consideration. The analysis of rock-forming minerals, which are a typical set for granites, with the help of a polarization microscope allowed us to determine the characteristic structures of the rock, to identify the presence of plagioclases and biotites of two generations, to detect partial substitution of quartz with a granular variety. The data of the silicate method allowed us to establish that the studied rock is characterized by an increased content of silica, the main alkali metals, and a very high alumina content. ICP-MS method data and their normalization with respect to S. S. San chondrite and the hypothetical plagiogranite COX showed that the rocks were formed from crustal-type melts saturated with rare-earth, as well as individual lithophilic elements (rubidium, barium). According to the diagnostic diagrams of J. A. Pierce, D. Papu, N. B. Harris, the formation of the studied massif occurred in the conditions of an intraplate geodynamic situation.

Results of local seismological monitoring in the Lena delta region

Refinement of the geodynamic situation in the area of the Lena River delta is relevant for understanding local geological processes. Previously, source seismology for this area was provided only by remote regional seismic stations. This paper shows the results of processing data from detailed seismological observations for 2018–2021. The distribution of earthquake hypocenters and their focal mechanisms are presented. The results of processing largely confirm the a priori geological data and do not contradict the results of regional observations. The accumulation of earthquakes in the area of the Kharaulakh Range most likely refers to the Primorsky Fault, which extends along the coast of the Bykovskaya channel. According to geological studies, the Primorsky Fault is a fault, which is confirmed by the focal mechanisms of earthquake sources in this area.

Современные методы, методики и технические средства мониторинга движений земной коры

This article gives an overview of available methods and techniques for geodynamic monitoring, such as the high-precision geometric re-leveling, high-precision linear-angular constructions, high-precision distance measurements, laser scanning, global navigation satellite systems, laser interferometers and strainmeters, radar satellite interferometry. The experience of applying these technologies in different physiographic regions is also described. The tools used in measurements, which provide the maximum achievable accuracy of methods in modern conditions, are demonstrated. A table is made with the summary characteristic of instrumental methods to measure the parameters of current movements of the Earth crust. On the basis of the performed comparative analysis of modern methods, techniques and technical means for execution of geodynamic monitoring, the most effective ones have been chosen from the methods listed above. Such methods include methods of high-precision geometric levelling of I and II classes, as well as the global navigation satellite systems. Complex use of these methods will allow to obtain reliable data about the geodynamic situation of the investigated area.

Environmental safety issues and challenges and geodynamic monitoring at the Karachaganak oil and gas condensate field

Purpose. Environmental safety evaluation and geodynamic monitoring of the Karachaganak oil and gas condensate field (KOGCF) explored on the north board of the Pre-Caspian depression in order to predict the consequences of long-term operation of this field. Methodology. Synthesis and system analysis of the articles and archival literature on environmental hazards and geodynamic monitoring of the complex methods, repeated levelling process, GPS-measurements, high-precision gravimetry and seismological monitoring. Findings. At a qualitative and quantitative level, the activation of vertical and horizontal movements of rock masses, changes in the field of local gravity anomalies, more frequent earthquakes whose hypocentres are located at depths comparable to the intervals of field development are substantiated. Trends and tendencies in the study on the relationship between the continuously changing geodynamic state of the subsoil and field-geological processes are outlined. All these manifestations in one way or another find manifestations in the environmental risks of the area of the exploited deposit. In the conclusions, it is recommended to carry out a set of measures to reduce environmental risks. Originality. The results of geodynamic monitoring at the KOGCF for the northern board of the Pre-Caspian depression for the first time made it possible to obtain convincing evidence in favour of noticeable seismic-deformation processes in the upper part of the earths crust under the influence of hydrocarbon production processes. Practical value. The conclusions obtained in the work confirm the necessity and binding of geodynamic monitoring in order to study and assess the possibility of different scenarios of geodynamic situations related to the development of hydrocarbon fields, are recommended for levelling factors of potential geodynamic risk at the KOGCF.

Моделирование вертикальных смещений в результате мантийной конвекции на профиле через Охотское море

Vertical motions, especially in the active continental margins such as Kuril-Kamchatka transition zone, are still pure studied. One of the factors significantly affecting the amplitudes and directions of vertical motions is mantle convections. Estimates of the amplitudes of vertical motions in region have been obtained by means of numerical modeling of the mantle convection made by the method of finite elements. The values of emergences in the area of Sakhalin Island and the Kuril Ridge from 0–3 to 13 m were obtained with the accepted rates of mantle convection from 1 to 5 mm/year. The results obtained should be taken into account when reconstructing neotectonic history of the region and assessing the geodynamic situation in the region of the Sea of Okhotsk.

The world-class mid-Mesozoic Jiangnan tungsten belt, South China: Coeval large reduced and small oxidized tungsten systems controlled by different magmatic petrogeneses

The 500 km-long NE-trending Jiangnan tungsten belt formed at 140–150 Ma at the northern margin of the Yangtze craton and has a total resource of approximately 6.0 Mt WO3. Most deposits are of granite-related porphyry/vein-style and skarn type. The three large W systems at Zhuxi, Shimensi and Shiweidong in the southwestern part of the belt are the most important. These deposits have reduced affinity and are related to ilmenite-series S-type granites. The many smaller W-Mo deposits in the northeastern part of the belt have oxidized affinity and are related to magnetite-series I-type granites. Based on geological features, magma formation temperatures, bulk-rock and biotite compositions, Sr-Nd-Hf isotope data and trace element modeling, we propose a model in which large, reduced W-related granitic magmas formed by crustal partial melting induced by intrusion of mantle-derived mafic magmas, followed by internal magmatic evolution. In contrast, the more oxidized W-Mo-related granitic magmas formed by hybridization of crustal melts and sills of mantle-derived mafic magma in hot zones, with minor magmatic evolution. This model explains the metallogenic features of the coeval large W and small W-Mo deposits in the Jiangnan belt and reveals that the magma source and corresponding oxidation state are the main controls on the significant size difference between the reduced and oxidized tungsten systems, although the general geodynamic situation is the same.

Advancing of the geomechanical forecasting system and substantiation of mining at rockburst hazardous deposits

The paper presents the main approaches and their advancing for the systems of rock mass stress-strain state forecasting during mining of adjacent rockburst hazardous deposits. Such systems based on the original Sigma GT software are used at several Russian mining companies which develop solid rock deposits, prone to brittle fracturing and undergoing the gravitational-tectonic stress-strain state. At that, the mining-induced impact on the rock mass is accompanied by occurrence of dynamic rock pressure. The geomechanical situation forecast systems have been applied directly at mining companies for more than 10 years and have shown their high efficiency. The efficiency is associated primarily with the operative calculation of stress-strain state in case of exacerbations of the geodynamic situation and the potential consideration of various mining options in order to reduce stress concentration and give recommendations for supporting and unloading measures in mine workings. In addition, the Sigma GT software is used in annual and long-term mining planning. Initially, such systems were developed for individual rockburst hazardous mining blocks, and their efficient operation time was limited to a 3-5 year period, that is, the block mining time. Further on, taking into account the needs of companies, the systems began to include a whole deposit or even several deposits. Being applied, the system is constantly developed and advanced and adapted to specific conditions and tasks. The most actual tasks are combination of the results of stress-strain state modeling with seismic monitoring data; creation of a hierarchical system of interconnected multiscale volume models; more complete consideration of structural heterogeneities of the rock mass and development of a recommendation block for safe mining operations, taking into account the geomechanical situation forecast data. The solution of these problems is considered on the example of a section of the Khibiny apatite arc, within which underground and open mining is carried out in the zone of mutual influence.

Underground operations in Internatsionalny mine rock mass susceptible to gas dynamic phenomena

Starting from 2019 extraction of diamond ore reserves from Internatsionalnaya pipe by Internatsionalny mine of ALROSA is carried out in complex geological and geomechanical conditions. Geodynamic situation is complicated by a few gas dynamic phenomena of different nature and scale recorded. The investigation results on gas release dynamics from dolomite rock mass during drivage of Spiral decline, in a test site on level.-802/-820 m in case of prediction and prevention measures undertaken to combat gas dynamic phenomena are presented. The dynamic characteristics of gas in outburst-hazardous dolomite rocks are calculated by the initial velocity of gas release. Efficiency of the current outburst hazard prediction method using facility MIG-Ts1 is proved. At the same time, it is necessary to perform additional studies to collect sufficient statistics and reliable data on gas release and gas pressure during drivage operations in the mine. The authors appreciate participation of Deputy CEO of VostNII Science Center, Doctor of Engineering Sciences, Professor V. S. Zykov, Doctor of Engineering Sciences, Professor A. V. Dzhigrin, Director of Research Center for Applied Geomechanics and Convergent Technologies in Mining at NUST MISIS College of Mining, Doctor of Engineering Sciences, Professor of the Russian Academy of Sciences V. A. Eremenko and Director of VNIMI’s Kemerovo Division, Candidate of Engineering Sciences P. V. Grechishkin.

ОЦЕНКА СОВРЕМЕННОЙ ГЕОДИНАМИЧЕСКОЙ СИТУАЦИИ ТАШТАГОЛЬСКОГО ЖЕЛЕЗОРУДНОГО МЕСТОРОЖДЕНИЯ

The results of GNSS observations in the area of protected objects in the mining influence zone are presented. For research, the Northwest section of the Tashtagol iron ore deposit was selected. This is the largest field in the Mountain Shoria. Directly in the area of the mine there is a sinkhole. This makes monitoring difficult. An analysis of the displacements of the earth's surface under anthropogenic im-pact is carried out. The finite element method and the model of locally uniform deformation of a triangular finite element were used. Surfer and Elcut software packages were used to determine the parameters of the deformation fields and their visualization. The article shows the change in shape and boundary, displacement and dilatation fields, deformation field along the x axis and deformation field along the y axis. The research results will help to substantiate an expert assessment of the geodynamic situation of the Tashtagol iron ore deposit at present and to make a reasonable forecast of the deformation situation of the deposit territory. This justifies the relevance of regularly conducted geodetic observations, which are also of environmental importance and industrial safety.

ГЕОДИНАМІКА

Purpose. Our research main purpose is to demonstrate the use of entropy maximization method for calculating the geochemical system composition, which consist of solid and gaseous organic substances. Changing the geodynamic situation is the driving force of elements redistribution between compounds in such systems. According to thermodynamic apparatus the main factors influencing this redistribution are pressure, temperature and the initial number of elements. Methods. Gibbs energy minimizing, maximizing the entropy, independent chemical reactions constants, Lagrange's method of undetermined multipliers, Newton–Raphson iterative method. It is well known that the fossilized organic matter, which is mainly represented by many types of kerogen, is an irregular polymer with structure, which cannot be described definitely. To calculate the equilibrium in the kerogen/gas system and obtain reliable results, it is necessary to apply a new model, without using the model structures of kerogen. We have proposed and described in detail a method of applying the Jaynes' formalism and maximizing entropy method to calculate the change in the composition of the kerogen/gas system with geodynamic regimes changing. Software in the Excel macros form and a compiled dynamic library, written in Visual Basic language, was created for calculations. Results. To verify the reliability of the proposed method and algorithm, we calculated the composition of the geochemical system, consisting of type II kerogen, methane to pentane hydrocarbons (including isomers), carbon dioxide, water and hydrogen sulfide. The calculation result is the molar fractions of hydrocarbon components and additive groups that make up kerogen, for different depths of the earth's crust. The calculations were performed for three heat fluxes: 40, 75 and 100 mW/m2, lithostatic pressure taken in account. Scientific novelty. It is established that the geodynamic situation changing in a complex way affects the distribution of elements between gases and kerogen in a closed thermodynamic system; modeling the kerogen/gas system behavior by method of entropy maximization provides results that do not contradict to study the structure of type II kerogen at different stages of maturity; the character of changes in the concentrations of hydrocarbon gases in equilibrium with type II kerogen indicates the inconsistency of the "oil window" hypothesis with the postulates of equilibrium thermodynamics. Practical significance. The entropy maximization method can be successfully used to calculate the composition of various geochemical systems consisting of organic compounds. The method is suitable for determining chemical composition of the irregular polymers, such as kerogen, bitumen, humic, in equilibrium with organic and inorganic gases and liquids.

Tectonic Fragmentation and Geodynamic Regime of Elbrus and Kazbek Volcanoes (Central Caucasus, Russia): Results of the Deep Geophysical Research

A comprehensive analysis of instrumental data was carried out to establish indicators of the geodynamic conditions of interaction between the Scythian Plate and the collage of southern plates; and to determine the type and kinematics of the Main Caucasian Thrust and the nature of volcanoes in the North Caucasus. In terms of structure and tectonics, the studies were conducted within the alpine structure of the Greater Caucasus, and they equally characterize both of its first-order structures: the folded-block uplift of the Main Range and the North Caucasian regional massif. In the kinematics of the Main Caucasian Thrust and volcanoes of the North Caucasus, there are no subduction elements. The absence of correspondence of the Main Thrust to the Benioff zone, and, conversely, its similarity to listric faults and shallow-focus volcanic centers are more consistent with a collisional geodynamic situation. Geological and geophysical sections along the network of regional profiles of deep geophysical studies in Ciscaucasia and the central part of the Greater Caucasus are characterized by similarity in the elements of the deep structure and semithrust kinematics of interaction with the consolidated crust of the southern microplates–terranes framing the Arabian Plate from the north. The volcanoes of the Central Caucasus arose in a collisional setting and a relationship between Elbrus volcano and the Main Caucasian Thrust as a collision compression structure is assumed. Data were obtained on the results of geophysical studies using the earthquake converted-wave method (ECWM), microseismic sounding method (MSM), magnetotelluric sounding (MTS), and gravimagnetic measurements in combination with data obtained from processing of satellite images of the specific length of lineaments of tectonic fragmentation for different depths of lithospheric sections. Laboratory determination of radiocarbon dating of volcanic complexes, distribution of the thermal field in surface and deep thermal springs, as well as isotopic assessment of the ratios of indicator elements of Elbrus volcano, which make it possible to confidently identify a magma chamber at depth of ~5 km and a magma chamber at depth of ~30–40 km. Our studies allow us to consider the main characteristics as an increased thermal field, variations in the helium isotope ratios, a seismic gap under the volcanic structure, and insignificant energy unloadings occurring on gentle low-power tectonic zones on the northeastern and eastern slopes, where periodic fumarole gas emissions are inherent to the active volcano.

Possible Source of the Deep Earthquake of October 15, 2018 in the Sea of Azov

Earthquakes in the Sea of Azov are quite commonplace. Until now, the idea of ​​their nature has focused on tectonic processes in the Earth’s crust. In our work, using morphotectonic analysis, we examined on a lithospheric scale the geodynamic situation in the collision zone of the East Black Sea Plate and the margin of the East European Platform, in order to show that not only in the crust, but also in the lower lithosphere, the necessary tectonic prerequisites exist for the accumulation of seismic energy with subsequent release in the form of earthquakes. Based on a case study of an earthquake that occurred on October 15, 2018, in the Sea of Azov, we showed the possible causes of its occurrence for two options of solving the seismological problem, obtained by the Geophysical Service of the Russian Academy of Sciences and including in the solution according to V.Yu. Burmin’s method. The following focal parameters are published on the Geophysical Survey website: latitude, 46.36; longitude, 37.18; depth, 5 km; mb= 4.3. The focal parameters were obtained for the solution using the Burmin method: latitude, 46.42564; longitude, 37.24274; H = 133.4 km. The mechanisms of two solutions were constructed; for a source with a depth of 5 km, the focal mechanism was obtained: a reverse fault, with the source confined to the intersection of Kalmius-Dzhiginsky and the Main Azov faults; for 133.4 km, a strike-slip fault, with the source confined to the intersection of the Gubkinsky-Central Azov, Kalmius-Dzhiginsky, and the Main Azov faults. The constructed model of collision of the continental lithosphere of the East European Platform and the subducting East Black Sea Plate shows that under conditions of weak compressive forces from the side of the Arabian indenter, a pseudosubduction situation is formed, as a result of which shear stresses occur in the deformable frontal part of the continental lithosphere of the East European Platform, transitioning to a reverse fault along the line of shear. During this process, seismic energy is accumulated, accompanied by weak and moderate earthquakes, of a reverse-fault type for the earth’s crust in the region of the Azov Rise, and a normal-fault type in the lower part of the wedge of the continental lithosphere as a result of its destruction. Regional morphotectonic analysis did not allow us to choose the most probable focal mechanism for the earthquake. However, it is noteworthy that the results of our research have shown that the occurrence of deep earthquakes has all the necessary tectonic prerequisites, despite the well-established opinion of seismologists about the exclusively crustal location of earthquakes in this region.

Evaluation and comparative analysis of stress and deformations in seismic hazard zones in Bulgaria and adjacent lands

In this paper an attempt to elucidate the geodynamic situation in Bulgaria and adjacent lands from a seismological point of view is proposed. The fault plane solutions of 418 earthquakes and corresponding stresses and deformations are also analyzed. For the purposes of the quantitative stress and strain modeling, a seismic zonation is carried out and the Bulgarian territory and surroundings are divided in nine seismic hazard zones. The main seismological and focal mechanisms characteristics for each zone are presented. The stress tensors for the zones/fault systems are calculated by inversion of the focal mechanisms data using the technique of Gephart [1990]. The released strain is computed by means of the moment tensors of focal mechanisms according to the relation of Kostrov [1974]. In general, the obtained mean strain tensors show some agreement with the calculated mean stresses. Several local discrepancies and the whole geodynamic situation are analyzed in the light of some present tectonic hypotheses. On the basis of the analysis of the seismicity, stress and deformation on the territory of North Balkans are presented.