A set of tectonophysical methods has been applied to reconstruct the neotectonic stresses of the southeastern Altai Mountains within the Chuya–Kurai depression and its framing structures. It is suggested that at the neotectonic stage, the tectonic structures of the Altai Mountains underwent a transformation of geodynamic conditions—a situation of sublatitudinal horizontal compression with predominant reverse-fault and transpressional movements along faults that existed up to the Neogene was replaced by horizontal shear conditions with a NNE and NE subhorizontal compression axis and WNW and NW extension axis. With such a stress field, the dominant NW-trending faults in this territory are mainly characterized by dextral strike-slip displacements, and NE-trending faults, by sinistral. Submeridionally trending faults that formed at the neotectonic stage show clear signs of extensional structures. A feature of the faults of the Chuya–Kurai depression according to these studies is a fairly small number of megafractures (indicators of shear displacements) in shear zones. This indicates dominant reverse-fault and transpressional movements over large disjunctive structures in the region in the Paleozoic and Mesozoic versus neotectonic shear movements. The results of the research are of practical importance in studying the regional seismicity.

— On September 27, 2003, the destructive Chuya (Altai) earthquake (magnitude 7.3), the strongest earthquake among those recorded in 1991–2022 in continental Russia, occurred near the southwestern border of the Chuya and Kurai basins in southeastern Altai. We have analyzed the seismic activity of this area and compiled the scheme of neotectonic stresses of the Chuya–Kurai Basin and adjacent structures. The modern and neotectonic stresses of southeastern Altai have been compared. The neotectonic stresses are retrieved using the structural-geomorphological method of shear stress reconstruction. It has been found that the orientation of the subhorizontal compression axis of the first rank changes from meridional to NNE and NE. The earthquake occurred in the region within which the largest faults of rank I (Kurai and Shapshal), SSW part of the prerecent Charysh–Terekta fault (we combine it at the neotectonic stage with the fault bounding the Chagan–Uzun block from the southeast in a common regional fault of rank I) were activated at the neotectonic stage in an setting of additional compression. A larger-scale stress field has been also reconstructed for the Chagan–Uzun rigid block that delineates the Chuya and Kurai basins. The neotectonic fault of the NW strike bounding the Chuya and Kurai basins from the southwest has been identified. The fault, we notionally called Bezymyannyi, is divided by smaller faults of SE orientation into three segments and is included in the large South Chuya fault zone. According to the data on strong earthquake focal mechanisms in the investigated region, a stable subhorizontal position of the compression axis has been established (as well as at the neotectonic stage). It is accepted that strong earthquakes occur in a compression setting. The mechanisms of earthquakes (mostly, aftershocks) related to the Chuya event indicate the concentration of thrust mechanisms within the Chagan–Uzun elevated block. This may be due to the ongoing uplift of the Chagan–Uzun block at the current stage. Along the Bezymyannyi fault, the earthquake focal mechanisms are mostly shear-type. This is the result of formation of a shear field under the shear displacement along the fault during the earthquake. Major seismic events occur mainly in a compression setting. Thus, the Chuya earthquake is caused by a subhorizontal compression setting (both regional and local), which is determined by comparing the neotectonic and modern stresses.

The latest structural elements, as extensively developed in the form of systems of uplifts and depressions, have been identified on the basis of the comparison of relief and geological data. These elements have been studied by interpretation of satellite images and topographic maps in the form of lineaments predetermined by disjunctive dislocations. As a result of the research, the neotectonic shear stresses fields have been reconstructed with the orientation of the submeridional compression axes of the rank I tectonic stresses, which is generally in agreement with the subhorizontal compression axes established in almost all regions of Northern Eurasia and, generally, oriented submeridionally.

An algorithm for calculating stress values proposed here is based on the results of reconstruction performed by L.A. Sim’s structural-geomorphological method for platform areas. This method makes it possible to determine the orientation of the axes of principal stresses for the shear zones from the lineament analysis of satellite images and photographs and Gzovsky’s palette, and to identify the lineaments characterizing the basement active faults which are covered by sediments. It is proposed that the dataset obtained will be subjected to the algorithm of the second-stage method of Cataclastic Analysis of faulting displacements, in which the Mohr diagram is used to calculate the stress values normalized for the cohesion strength of the massif. The further determination of the cohesion strength and absolute stress values is based on the data for lithostatic pressure and fluid pressure in the fracture-pore space of the massif (either measured or prescriptive). The stress calculation algorithm was tested on a small area (60 square km of satellite imagery) near the territorial district of Seversk – the southern border of the West Siberian Platform. The calculations have shown that with the fluid pressure variations ranging from hydrostatic values to twice higher than those, the cohesion strength of a rock mass at the base of the sedimentary cover (500 m depth) is in the range of 41.0 to 16.8 bar, and the level of maximum tangential stresses lies in the range of 75 to 31 bar.

The stress-and-strain state of the rock massif and the kinematic type of faults of the Vuoksi fault zone (Karelian Isthmus) for the latest stage of tectonic history were determined by field tectonophysical methods. The main information was obtained from geological stress/strain indicators, which were mostly represented by measurements of minor faults and slickensides with kinematic information (the direction of relative displacement) on the fault plane. Near the Vuoksi fault zone, systems of faults with an orientation close to the strike of this regional fault structure are observed. Most widespread are strike-slip faults, whereas faults with normal or reverse displacement make up less than a quarter of the total number of faults. The STRESSgeol software based on the method of cataclastic analysis was used to restore stress-and-strain state. The variable orientation of the principal stress axes was determined in the studied area. The two main directions of maximum compression are NE-SW (to ENE-WSW) and NW-SE (to WNW-ESE). The axes of the maximum deviatory extension are subhorizontal and are directed in the NNE-SSW and NW (to WNW-ESE) direction. The intermediate axis often occupies a subvertical position. The horizontal shear stress state type prevails for the entire zone, and lateral shear displacements are also characteristic of this fault zone. This stress state type of the studied part of the Baltic Shield is significantly different from the stress state type of orogenic belts, where, along with horizontal shear stress state type, the situation of horizontal compression stress state type dominates. The obtained variability of the directions of maximum compression in the studied area can be preliminarily correlated with the previously identified zone of "unstable tectonic stresses" of the East European Platform.

The article presents data on the stress state of the Schmidt Peninsula of Sakhalin Island, obtained as a result of field tectonophysical studies in 2020. The importance of studying the northern part of Sakhalin is due to the prospects of this region for the minerals search. The performed studies allowed us to establish differences in the geodynamic condition between the western and eastern coasts of the peninsula. In general, the conditions of horizontal shear (shear type of deformation) prevail among the types of stress state in the studied territory. On the east coast, there are many situations of horizontal extension, which are usually confined to the axial parts of anticlinal structures. The west coast is characterized by the stable orientation of the axis of maximum compression in the NW direction and its subhorizontal position. For the east coast, the direction of the reconstructed orientations of maximum compression is characterized by greater variability. According to the data of the reconstruction, the stress-and-strain state pattern of the Schmidt Peninsula has significant differences from the main territory of Sakhalin Island.

Spatial reconstruction of tectonic stresses within the Subpolar Ural quartz crystal-containing province was conducted by the kinematic method [Gushchenko, 1973, 1979] based on the main indicators of tectonic stresses on slickensides. Local stress states (LSS) and general stress fields for large blocks were reconstructed by the method described in [Sim, Marinin, 2015]. In the blocks with numerous occurrences of quartz crystal (Pelingichey and Omega-Shor blocks), the general stress fields is characterized by a stress state close to uniaxial tension, i.e. the Lode-Nadai coefficient µ=–1. In these blocks, thick quartz veins are perpendicular to the tension axis of the general stress field. In the block without quartz crystal (West Saled), the general stress field is characterized by a triaxial stress state or pure shear state (–1˂µσ˂+1). The LSS of the quartz crystal deposits show the following: the stress state of µ=–1 is typical of quartz veins without quartz crystal nests, and a special kind of stress state is reconstructed near the nests with piezoelectric material. It is named a variation of the type of stress state (VTSS), which means that within one tectonic stage, the type of stress state changes approximately as follows: µσ=+1 (40 %), µσ=–1 (40 %), and –1˂µσ˂+1. It means that in the piezoelectric mineral deposits, pulsating tectonic stresses provided for a fluid flow of hydrothermal solutions at the intersection of ore-bearing and ore-controling faults when tension (µ=–1) was replaced with compression (µ=+1), while the orientations of compression and tension axes remained unchanged. Apparently, such a regime was caused by alternating activation of the above-mentioned faults. The tectonic stress reconstructions were performed for 33 mineral deposits and occur­rences of quartz crystal. VTSS was determined in 32 deposits; one mineral occurrence is characterized by uniaxial tension. Therefore, we propose using VTSS (variation of the type of stress state) as a criterion for predicting the locations of quartz crystal deposits.

To verify the ideas about neotectonic and modern stresses of Sakhalin, we analyze structural and geomorphological signs of the stress state of this region, discovered during field work in 2019–2020. Along with updated field measurements using the structural-geomorphological method, data on crustal deformation based on GPS/GLONASS measurements are presented. Data from geophysical studies (seismological and borehole methods) are given. The identification of three types of areas with different geodynamic regime: transtension, transpression and strike – slip (simple shift) is confirmed. Variations of the current stress field at the boundaries of regions with different geodynamic regime for the formation of new faults are noted. Northern Sakhalin has specific directions of compression axes of neotectonic stresses, expressed in North-Eastern orientations, in contrast to the prevailing sublatitudinal orientations on the entire island. Studies have shown that in the south of Sakhalin, the border between the Amur and Okhotsk microplates runs along the West Sakhalin fault rather than the Central Sakhalin fault.

Для верификации представлений о неотектонических и современных напряжениях Сахалина анализируются структурно-геоморфологические признаки напряженного состояния этого региона, обнаруженные в ходе полевых работ 2019–2020 гг. Наряду с новыми полевыми замерами структурно-геоморфологическим методом представлены данные о деформации земной коры на основе GPS/ГЛОНАСС-измерений. Приводятся данные геофизических исследований (сейсмологических и скважинных методов). Подтверждено выделение трех типов областей с различной геодинамической обстановкой растяжения, сжатия и чистого сдвига. Отмечены вариации современного поля напряжений на границах областей с различной геодинамической обстановкой формирования новейших разломов. Северный Сахалин имеет специфические направления осей сжатия неотектонических напряжений, выраженные в северо-восточных ориентировках, в отличие от преобладающих субширотных ориентировок на всем острове. Проведенные исследования показали, что на юге Сахалина граница между Амурской и Охотской микроплитами проходит, скорее, по Западно-Сахалинскому, а не по Центрально-Сахалинскому разлому.

—Paleostress inversion may be ambiguous when several markedly different local stress states are inferred for a group of outcrops. Attempts of reconstructing regional stress regimes (compressional, extensional, or strike-slip) by selecting local principal stresses of proximal directions turn out to have poor grounds. Each stress permutation (e.g., extension to compression) attendant with buildup of large irreversible strain (fault slip) requires a 5–6 kbar change in middle-crust horizontal stress and at least 50 Myr stable and uniform loading. Tectonophysical stress reconstructions for present active intracontinental orogens show heterogeneous patterns: Stress directions in uplifts are different from those in large intermontane basins and even in relatively subsided parts of mountain ranges or in adjacent uplifted zones (e.g., a plateau and a range). Paleostresses should be interpreted with reference to present stress fields in the respective areas. It is suggested to reconstruct regional stresses using the approach of L. Sim implying search for “common stress fields”. Another important technique is to trace stress changes in specific structures (large folds etc.) in the course of their evolution. The available data indicate correlation and bipolarity of stress states in large basins and uplifts.

Аннотация.Вдоль зоны Вуоксинского глубинного разлома полевыми тектонофизическими методами определены характеристики напряженно-деформированного состояния массивов горных пород, а также кинематический тип разломов на новейшем этапе.Полученные данные показали в исследованном районе разнообразие ориентировок осей главных нормальных напряжений

Аннотация.Работа посвящена сопоставлению результатов сейсмических, неотектонических исследований с применением нового программного обеспечения SGM-SIM.Собраны данные по механизму очага землетрясения и направления главных осей сжатия новейшего возраста, восстановленных структурногеоморфологическим (СГ) методом Л.А.Сим (1991), по которым был подтвержден результат, полученный ранее при более мелкомасштабных исследованиях -на севере Русской плиты господствует субмеридиональное сжатие.Гордеевым Н.А.и Молчановым А.Б. ( 2018) создано программное обеспечение SGM-SIM по восстановлению сдвиговых тектонических напряжений, которое основано на СГ методе Л

Комплексом геологических, структурно-геоморфологических и тектонофизических методов изучена новейшая геодинамика восточной окраины Сибирской платформы, включающей Оленекский и Мунский своды на северо-восточной периферии Анабарской антеклизы, Вилюйскую синеклизу и западную часть Предверхоянского прогиба. Впервые составлена схема новейшей геодинамики восточной части Сибирской платформы масштаба 1:500 000. Выявлено доминирование сдвигового типа напряженного состояния и выделены разломы, сформированные в неотектонический этап в разных геодинамических обстановках. Установлено, что механизм формирования Оленекского и Мунского поднятий обусловлен внутриплатформенными источниками тектонических напряжений. Для оценки степени унаследованности разновозрастных структурных планов периферии Анабарской антеклизы созданы 3D-модели поверхности осадочного чехла и фундамента. Крупные новейшие структуры – Оленекское и Мунское сводовые поднятия, Кютингдинский прогиб и Бурская впадина – на протяжении длительной геологической истории развивались унаследованно, а Предверхоянский прогиб и кряж Чекановского отнесены к инверсионным структурам. Показано, что главные особенности неотектонического структурного плана изученной территории определяют новейшие активно развивающиеся Оленекское поднятие и Верхоянский хребет. Ключевые слова: тектоника, напряженное состояние, геодинамика, Оленекский свод, Вилюйская синеклиза.

Summary In the article, the tectonophysical conditions of quartz crystal formation, and modern geological hazards are discribed. For the study, next ways were applied: the kinematic method of analysis of displacement vectors on slickensides ( Gushchenko, 1973 ), way of determinating regional stress fields from data of local tectonic stresses in individual volumes of the earth’s crust ( Sim, 1982 ); structural-geomorphological (SG) method of a reconstruction of the shear stress on platforms ( Sim, 1991 ; Sim, Sergeev, 1996 ). At a prediction of hydrothermal mineral deposits, it was discovered that the reconstructed tectonic stresses along displacement vectors on slickensides refer to the newest and Late Hercynian orogeny stages of development; it is the time of formation of patch of quartz crystal. In crystals of quartz crystal, repeated opening of the nests is discovered. This is explained by the “variation of the kind of the stressed pattern”. The reasons for the formation of karst are identified at the training ground of Nizhny Novgorod, near the city of Dzerzhinsk and causes of increased accidents on the railways Moscow-Smolensk are diagnosed.

The article presents the results obtained by field tectonophysical methods applied to study tectonic stresses of the Northern Eurasia regions, including young and ancient platforms (West European, Timan–Pechora, Turan, West Siberian, East European, and East Siberian) and orogenic frame structures (Caucasus, Northern Tien Shan, Mongolia-Okhotsk system of mesozoids, and Sakhalin Island). Tectonic stress reconstructions provided the basis for analysing the influence of spreading in the North Atlantics and the Arctic on the stress state of the platforms in Northern Europe. A spatial boundary of the influence goes approximately along the margins of the Fennoscandian shield and the Russian plate in the north. Further southwards, the boundary is submeridional and extends from the western wing of the Byelorussian anteclise almost to the Eastern Carpathians. The stress reconstructions for this boundary show the WNW and W-E-trending axes of compression. The boundary line does not coincide with the Teisser-Tornquist line that represents the boundary between the platforms with heterochronous basements. However, it correlates well with heat flow anomalies. The boundary area is confined to the Baltic coast [Sim, 2000. Along the boundary area, near the Baltic Sea, there is an area wherein faulting is mainly caused by extension [Sim, 2000. In this setting, helium permeability is the highest, as shown by the crust map of the European part of the USSR [Eremeev,1983. Extension in this area is probably related to formation of young grabens in the Baltic shield. Changes in the compression axis orientation may be due to the alternating activations of the grabens in the submeridionalBotnicGulf and the latitudinalGulf of Finland. Reconstructions for individual faults show contradictions in the directions of shear displacements: both right- and left-lateral displacements are possible on the same fault segments, and the axes of compression can have either latitudinal or meridional orientations. The focal mechanisms of the Osmussaar andKaliningrad earthquakes (meridional and latitudinal axes of compression, respectively) give evidence of specific current neotectonic stresses in this area. Another zone is distinguished at 52°N from the above-described area. It is mainly sublatitudinal and detected along the southern flank of the Byelorussian anteclise. Further to the east, its orientation changes to SSW, and it roughly follows the SW boundary of theVoronezh anteclise. Reconstructions for the Ukrainian Shield, located south of this zone, show mainly the unstable orientations of the axes of compression. For the platforms inNorthern Eurasia, the tectonophysical methods reconstructed neotectonic stresses in the structures formed under the influence of intraplatform tectonic stresses. These are the residual gravitational horizontal compression stresses released by long-term denudation and uplifting of the structures, including the Khibiny massif of the Baltic Shield, theOlenek and Munsky massifs of the East Siberian platform. These structures are composed of the ancient Archaean-Proterozoic rock complexes, which have been subjected to predominantly vertical displacements for a long time, from the Paleozoic to the modern stage. Special attention should be given to the tectonic stresses ofSakhalin located at the boundary between the Eurasian and North American lithospheric plates. At the edges of these two largest plates, there are the Amur and Okhotsk microplates separated by theCentral Sakhalin fault, as described in some publications. Neotectonic stress reconstructions forSakhalinIsland show sublatitudinal compression and submeridional extension in the common stress field of shearing. The tectonophysical studies show that the neotectonic stresses differ in large structures: horizontal compression and shearing are typical of the uplifts (Kola Peninsula, Tien Shan, Sakhalin), while horizontal extension and extension with shearing are characteristic of depressions (Kandalaksha graben, depressions of theTatarGulf and theSea ofOkhotsk). Our studies provide the data on spacious ‘white spots’ in the modern stress maps ofNorthern Eurasia. The stress reconstructions for practically all the studied structures show that shearing is the dominant geodynamic regime in the study region.