Актуальность. Исследование глубинного строения в контактных зонах литосферных блоков в сопоставлении с сейсмичностью и регистрируемыми современными движениями имеет важнейшее значение для правильного понимания геодинамических процессов. Кавказская коллизионная зона характеризуется высокой геодинамической и тектонической активностью и сейсмичностью. Формирование тектонической структуры горно-складчатого сооружения Кавказа (далее - Кавказа) связано, в первую очередь, с напряжениями субгоризонтального сжатия, ориентированными, в общем, вкрест простирания и на современном этапе развития такие напряжения играют определяющую роль. С целью представления тектонического процесса в рамках единой кинематической модели была поставлена задача объединения структур Большого Кавказа, Осетинской впадины и Сунженского хребта единым глубинным геофизическим разрезом. Методы.Для построения структур Большого Кавказа, Осетинской впадины и Сунженского хребта единым глубинным геофизическим разрезом был применён метод микросейсмического зондирования (ММЗ). Результаты. Предложена кинематическая схема тектонических движений, которая позволяет объяснить наличие в тектонической зоне северной моноклинали Кавказа серии падающих на север надвигов и взбросов. При коллизии складчато-глыбового горного сооружения Кавказа и Скифской плиты верхний слой 8-11 км надвигается на Кавказ быстрее, проскальзывая по контакту 8-11 км, и создает листрику Владикавказского разлома. Сдвиг идет по поверхности фундамента, что объясняет сейсмичность, приуроченную к границе фундамент-осадки на глубине около 10 км. В районе Владикавказского разлома при столкновении с консолидированным приподнятым массивом Кавказа происходит процесс выпучивания осадочной толщи. Сунженский хребет является промежуточной складкой этого процесса. Зафиксированное спутниковыми геодезическими измерениями более быстрое поднятие бортов Владикавказского разлома по сравнению с его центральной частью объясняется тем, что для южной ветви разлома это связано с задиранием осадочного толщи при столкновении с приподнятым глыбовым фронтом Кавказа. Над северной ветвью разлома формируется независимый фронт поднятия. Relevance. The study of the depth structure in the contact zones of lithospheric blocks in comparison with seismicity and recorded recent movements is of utmost importance for the correct understanding of geodynamic processes. The Caucasian collision zone is characterized by high geodynamic and tectonic activity and seismicity. The formation of the tectonic structure of the Caucasus mountain-fold structure (hereinafter referred to as the Caucasus) is primarily associated with subhorizontal compression stresses oriented, in general, across the strike, and at the present stage of development such stresses play a determining role. In order to represent the tectonic process within the framework of a unified kinematic model, the goal was set to unite the structures of the Greater Caucasus, the Ossetian Depression and the Sunzhensky Ridge by a single deep geophysical section. Methods. The method of microseismic sounding was applied to build the structures of the Greater Caucasus, the Ossetian Depression and the Sunzhensky Ridge as a single deep geophysical section. Results. A kinematic scheme of tectonic movements is proposed, which allows to explain the presence of a series of northward-dipping thrusts and thrusts in the tectonic zone of the northern monocline of the Caucasus. During collision of the fold-and-boulder mountain structure of the Caucasus and the Scythian plate, the upper 8-11 km layer thrusts faster into the Caucasus, slipping across the 8-11 km contact, and creates the listric of the Vladikavkaz fault. The thrusting is along the basement surface, which explains the seismicity confined to the basement-sediment boundary at a depth of about 10 km. In the vicinity of the Vladikavkaz fault, the sedimentary strata is bulging as it collides with the consolidated uplifted massif of the Caucasus. The Sunzhensky Ridge is an intermediate fold of this process. The faster uplift of the sides of the Vladikavkaz fault as compared to its central part recorded by satellite geodetic measurements is explained by the fact that for the southern branch of the fault it is associated with the bulging of the sedimentary strata during collision with the uplifted clastic front of the Caucasus. An independent uplift front is formed above the northern branch of the fault.

Актуальность. Исследование глубинного строения в контактных зонах литосферных блоков в сопоставлении с сейсмичностью и регистрируемыми современными движениями имеет важнейшее значение для правильного понимания геодинамических процессов. Кавказская коллизионная зона характеризуется высокой геодинамической и тектонической активностью и сейсмичностью. Формирование тектонической структуры горно-складчатого сооружения Кавказа (далее - Кавказа) связано, в первую очередь, с напряжениями субгоризонтального сжатия, ориентированными, в общем, вкрест простирания и на современном этапе развития такие напряжения играют определяющую роль. С целью представления тектонического процесса в рамках единой кинематической модели была поставлена задача объединения структур Большого Кавказа, Осетинской впадины и Сунженского хребта единым глубинным геофизическим разрезом. Методы. Для построения структур Большого Кавказа, Осетинской впадины и Сунженского хребта единым глубинным геофизическим разрезом был применён метод микросейсмического зондирования (ММЗ). Результаты. Предложена кинематическая схема тектонических движений, которая позволяет объяснить наличие в тектонической зоне северной моноклинали Кавказа серии падающих на север надвигов и взбросов. При коллизии складчато-глыбового горного сооружения Кавказа и Скифской плиты верхний слой 8-11 км надвигается на Кавказ быстрее, проскальзывая по контакту 8-11 км, и создает листрику Владикавказского разлома. Сдвиг идет по поверхности фундамента, что объясняет сейсмичность, приуроченную к границе фундамент-осадки на глубине около 10 км. В районе Владикавказского разлома при столкновении с консолидированным приподнятым массивом Кавказа происходит процесс выпучивания осадочной толщи. Сунженский хребет является промежуточной складкой этого процесса. Зафиксированное спутниковыми геодезическими измерениями более быстрое поднятие бортов Владикавказского разлома по сравнению с его центральной частью объясняется тем, что для южной ветви разлома это связано с задиранием осадочного толщи при столкновении с приподнятым глыбовым фронтом Кавказа. Над северной ветвью разлома формируется независимый фронт поднятия.

The paper presents the velocity field of the Western Caucasus and Ciscaucasia based on GNSS observations. In the ITRF2014 reference frame, this field shows the coordinated movement of the region in the north‒northeast direction at an average rate of 27‒28 mm/year. A number of geodynamic features of the main tectonic structures of the region are identified with respect to fixed (immobile) Eurasia. In the northern part of the region, a fan-shaped pattern of horizontal velocity vectors is observed, reflecting counterclockwise rotation of the northern limb of the North Azov flexural fault zone and, accordingly, modern shear displacements. To detail the geodynamic situation, the velocity field is compared with two geodetic profiles. The first profile crosses in the southwest–northeast direction the mountain belt of the Western Caucasus, the West Kuban Foredeep, and the Scythian Platform, which are the region’s main geological structures. The second profile is less extended, but also crosses the entire mountain belt of the Western Caucasus, the West Kuban Foredeep, and part of the monocline of the Central Sector of the North Caucasus. Within the Greater Caucasus and the West Kuban Foredeep, transverse compression of the main morphostructures is observed at a rate of up to 1 mm/year, and shear displacements prevail in the Ciscaucasia. The mountain belt of the Western Caucasus is in conditions of longitudinal compression. East of the Tuapse Fault Zone, the mountain belt is undergoing longitudinal extension. At the same time, the intensity of deformation processes on the southern slope area is higher than in the Ciscaucasia. Currently, the seismic activity level in the Western Caucasus is low and moderate.

From a new gravity data set that covers homogeneously the whole surface of Gran Canaria (Canary Islands, Spain) and marine gravity data in the nearest offshore, we have obtained a Bouguer anomaly gravity map of the island which improves the previous ones. Using these gravity anomalies, we have applied a gravity inversion approach to investigate the structures beneath the surface of Gran Canaria Island and derive a 3D gravity sources model. The geometry of structures with anomalous density values is constrained up to a depth of approximately 20,000 m below the sea level. The interpretation of the density model identified structures related to the different volcanic stages of Gran Canaria. Several deep-rooted high-density structures represent the intrusive bodies emplaced in the early formation of Gran Canaria and the magma plumbing system of the Miocene volcanic edifices. A low-density body in the center of the island may be associated with the syenitic core of the felsic central volcanic edifice (Tejeda Caldera). Shallow low-density structures identified fractures which acted as feeder dikes of monogenetic volcanoes during the rejuvenated stage. Finally, the NW-SE rift, which is the most important volcano-tectonic structure of Gran Canaria, has a characteristic gravimetric signature and represents a long-lived extensional fracture zone that has controlled the volcanic activity at least since the Miocene.

The article presents a numerical study of the formation of the amplitude response in a free surface from simultaneous scattering of Rayleigh waves and vertically incident longitudinal waves by an embedded contrast velocity inclusion. It has been established that the significant presence of body waves in a microseismic field does not fundamentally change the result of the microseismic sounding method, which is based on the notion of the overwhelming contribution of the fundamental mode of a Rayleigh wave to the formation of the Earth’s microseismic field. Cases are considered when a microseismic signal at the same frequency is modeled only by the fundamental mode of the Rayleigh wave, only by a vertically incident longitudinal wave, and by both types of waves simultaneously. Variants of inhomogeneities with different dimensions and velocity properties are considered. The analysis was performed in a (λ, r)-space, in analogy with reconstruction of the structure of the geological setting in the microseismic sounding method, where λ is the wavelength of the fundamental Rayleigh mode and r is the coordinate on the Earth’s surface.

Abstract—In 2014–2019, integrated geological and geophysical studies were carried out in the largest flexural-rupture and fold-and-fault zones of the Northwest Caucasus (the Anapa, Akhtyr, Moldavanovka, Karabetov, Fanagoria and Azov anticlinal ridges and the Pshekha–Adler, Kerch–Tuzla, and Kerch Strait faults). Microseismic sounding method (MSM) was the main geophysical approach. The MSM studies identified the deep structural features of the Earth’s crust in the study region and made it possible to correlate them with the specific tectonic structures on the surface. The correlation was established by reconciling the results of the MSM studies, the parameters of sedimentary cover section, and crustal discontinuities revealed by drilling and previous studies of the converted waves from the earthquakes. It is found out that the Anapa flexure and longitudinal tectonic zones have the distinct deep roots beneath them. The trans-Caucasian Anapa flexural-rupture zone separates the pericline of the Northwest Caucasus from the region of the Taman Peninsula, whereas longitudinal flexures and fault structures divide the meganticlinorium from the subsided West Kuban and Azov blocks of the northern slope of the folded system and from the Kerch–Taman trough of the southern framing of the Northwest Caucasus. The faults in the study region are distinguished into deep faults penetrating into the lower crust and even reaching the upper mantle and near-surface faults localized within the sedimentary cover in the Earth’s interior. The seismogenic role of these tectonic deformations in the studied seismic region is determined.

С помощью численного моделирования исследованы некоторые закономерности взаимодействия фундаментальных мод Рэлея с заглубленными неоднородностями различных размеров и скоростных контрастов. Рассчитано поле колебаний на поверхности вблизи рассеивающих неоднородностей в зависимости от частоты. Полученные синтетические сейсмограммы использованы для моделирования предложенной ранее технологии микросейсмического зондирования – оценки решения обратной задачи строения среды с включениями на основе использования фонового микросейсмического поля и предусматривающей простую связь глубины восстанавливаемого слоя и регистрируемой частоты в спектре микросейсм с помощью численного коэффициента приблизительно равного 0.4–0.5. Результаты прямого моделирования совместно с оценкой обратной задачи подтверждают корректность технологии микросейсмического зондирования для оценки структуры среды, которая ранее базировалась исключительно на экспериментальных наблюдениях и носила феноменологический характер. Исследован ряд взаимосвязей между скоростными параметрами исходных неоднородностей и их изображениями после восстановления.

The structure of the fault system of northeastern Bulgaria and, in particular, of the Intramoesian fault, is examined in order to assess their current activity. The Intramoesian fault and its branch disjunctives have not been sufficiently studied from the geological-geomorphological and seismological points of view. The authors conduct a complex of geophysical investigations and obtain an idea of their deep structure. The system of these faults is a key element in solving the problem of assessing the seismic hazard of the region, since recent studies of this territory indicate the existence of traces of relatively young seismotectonic processes. There is also an opinion that the zone of the two Intramoesian faults disturbs the eastern part of the tectonic plate, which is subducted under the Carpathian fold system in the region of the Vrancea Mountains. The results of the field study of the southeastern Bulgarian part of these fault systems by a complex of geological-geomorphological, paleoseismological, and archeoseismological methods are presented. The zone of the Intramoesian fault is structurally segmented and the features of its intersection with the disjunctives of another structural orientation are revealed based on this. The data that determine the degree of its geological and seismic activity are discussed.

In the period from 2007 to 2017 complex geological and geophysical studies were carried out in the three largest flexural-rupture fault zones in the North-West Caucasus (Anapa, Akhtyrka and Moldavan). The micro-seismic sounding (MSM) was used as the main geophysical method. Studies with the help of MSM allowed us to identify the features of the deep structure of the earth’s crust in the study area and to associate them with specific tectonic structures on the surface.The binding was carried out by harmonizing the results of the MSM and the parameters of the section of the sedimentary cover and crustal boundaries according to the drilling data and the work previously performed by the reflected wave method (MOVZ). It was found that the Anapa flexure and longitudinal tectonic zones have clear deep roots, and also separate the pericline of the North-Western Caucasus from the Taman Peninsula and from the lowered blocks of the Northern slope of the folded system.Faults in the study area are divided into: (1) deep faults of the Caucasian stretch, penetrating into the lower crust and even to the upper mantle, and (2) near-surface faults, do not extend to the depths beyond the thickness of the sedimentary cover. The seismogenic role of these tectonic disturbances in the studied seismically active region has been determined.

The paper is devoted to the analysis of the results of a two-dimensional numerical solution of the direct scattering problem of the fundamental Rayleigh mode on two velocity inhomogeneities located one under another. This model made it possible to analyze some cases of using the method of microseismicsounding (MMS) in conditions of complex structured media. Using the numerical model built from first principles in direct modeling, we obtained estimates of the vertical resolution of the microseismic sounding method. The cases of a number of specific geometrical dimensions and a number of elastic parameters of inclusions with values close to those encountered in natural conditions are considered. Simple practical methods have been developed and formulated, with the help of which one can estimate the vertical resolution of objects when interpreting microseismic sounding sections obtainedexperimentally. Estimation of the vertical resolution of the MMS on synthetic data is that, if the distance between the centers of two small inhomogeneities, one above the other, compared to the depth, is 36‑41 % (or more) of the fundamental mode of the Rayleigh wave, equal to λR = Hcenter/ 0.4, where Hcenter is the midpoint depth between the centers of inhomogeneities, then the images of these inhomogeneities will be resolved in the field of random Rayleigh waves. That is, to ensure the resolution of the MMS, the vertical distance between the centers of small discontinuities should be Hcenter or more. The techniques developed were used to assess the resolution of horizontally-lying layers in the sections obtained during the study of the junction zone of the Taman Peninsula and the Crimea in the course of geological interpretation of microseismic research results.

The article summarizes the available and newly collected data on the near-surface and deep structure and modern geodynamics of key regions of the northwest part of the Greater Caucasus. Models of the fault-block structure of this orogen and the nature of seismogenic displacements along the faults on its northwest pericline have been developed. The reasons for the abrupt change of the fold-block structure in the area of the Anapa seismogenerating flexural-fault zone are clarified. Detailed models of the near-surface and deep structure were constructed for a number of the most important seismogenerating structures in the Northwestern Caucasus that caused the Lower Kuban-II earthquake on November 9, 2002, with M = 4.7, and the Su-Psekh event on December 10, 2012, with M-w = 4.3, as well as the Pshekh earthquake on November 15, 2004 in Krasnodar krai with M = 4.6. Three-dimensional geodynamic and seismotectonic models of seismogenerating structures were constructed based on the results of field geological and geophysical surveys.

Работа посвящена анализу результатов двумерного численного решения прямой задачи рассеяния фундаментальной моды Рэлея на двух скоростных неоднородностях, расположенных друг под другом. Данная модель позволила проанализировать некоторые случаи использования метода микросейсмического зондирования (ММЗ) в условиях сложно построенных сред. С использованием численной модели, построенной из первых принципов в прямом моделировании получены оценки вертикальной разрешающей способности метода микросейсмического зондирования. Рассмотрены случаи ряда конкретных геометрических размеров и ряда упругих параметров включений, со значениями, близкими к встречающимся в природных условиях. Выработаны и сформулированы простые практические приемы, с помощью которых можно оценивать вертикальное разрешение объектов при интерпретации разрезов микросейсмического зондирования по экспериментально полученным разрезам. Оценка вертикальной разрешающей способности ММЗ на синтетических данных состоит в том, что, если расстояние между центрами двух малых по сравнению с глубиной залегания неоднородностей, расположенных друг над другом, составляет 36 41 (или более) от длины фундаментальной моды волны Рэлея, равной R Нcenter/ 0,4, где Нcenter глубина середины между центрами неоднородностей, то изображения этих неоднородностей будут разрешены в поле случайных волн Рэлея. То есть, для разрешимости по ММЗ расстояние по вертикали между центрами малых неоднородностей должно составлять Нcenter или более. Выработанные приемы использованы для оценки разрешения горизонтально залегающих слоев в разрезах, полученных в ходе изучения зоны сочленения Таманского полуострова и Крыма при геологической интерпретации результатов микросейсмических исследований. The paper is devoted to the analysis of the results of a twodimensional numerical solution of the direct scattering problem of the fundamental Rayleigh mode on two velocity inhomogeneities located one under another. This model made it possible to analyze some cases of using the method of microseismicsounding (MMS) in conditions of complex structured media.Using the numerical model built from first principles in direct modeling, we obtained estimates of the vertical resolution of the microseismic sounding method. The cases of a number of specific geometrical dimensions and a number of elastic parameters of inclusions with values close to those encountered in natural conditions are considered.Simple practical methods have been developed and formulated, with the help of which one can estimate the vertical resolution of objects when interpreting microseismic sounding sections obtainedexperimentally.Estimation of the vertical resolution of the MMS on synthetic data is that, if the distance between the centers of two small inhomogeneities, one above the other, compared to the depth, is 36 41 (or more) of the fundamental mode of the Rayleigh wave, equal to R Hcenter/ 0.4, where Hcenter is the midpoint depth between the centers of inhomogeneities, then the images of these inhomogeneities will be resolved in the field of random Rayleigh waves. That is, to ensure the resolution of the MMS, the vertical distance between the centers of small discontinuities should be Hcenter or more. The techniques developed were used to assess the resolution of horizontallylying layers in the sections obtained during the study of the junction zone of the Taman Peninsula and the Crimea in the course of geological interpretation of microseismic research results.

Analysis of GPS-measurements made for the first time along the geodesic profile crossing all the main geological structures in the Ossetian region of the Greater Caucasus showed that significant jumps in the velocity of horizontal movements are observed in zones where strong earthquakes recently occurred. Interpretation of the measurement data is performed in comparison with the results of neotectonic and seismotectonic studies and data on deep structure of the region. The maximum decrease in the current transverse shortening rates is recorded in the zones of the Vladikavkaz and Kakheti–Lechkhum faults. The zone of the Vladikavkaz Fault hosted the source of the Khataldon earthquake of May 11, 2008, M = 4.5, I = 4 in the epicentral zone. Epicentral zones of earthquakes such as the 1991 Racha with М = 7.0, 1991 Dzhava with М = 6.2, Oni-I of February 6, 2006 with М = 5.0, and Oni-II of September 7, 2009 with М = 6.0 involved the upper crustal blocks within the limits of the Kakheti–Lechkhum suture zone at the base of the southern slope of the Greater Caucasus. The previously predicted significant decrease in the rate of horizontal movements after seismic activations in these areas of catastrophic seismic events of 1991, 2006, and 2009 on the southern slope of the Greater Caucasus is confirmed.

The article highlights the results of the first GPS measurements carried out along a geodetic profile that intersects all major geological structures in the Ossetian region of the Greater Caucasus. The interpretation of the measurement results was made in comparison with the results of neotectonic studies and data on the deep structure. The maximum decrease in the current transverse compression velocities was recorded in the region of the highest rise above the Earth's surface of a low-Q volume of the Earth's crust, which has a widening effect on the entire mountain structure. The presence of significant transverse displacements of the surface reflects the shear component along the largest faults of the Caucasian strike. The previously prognosticated significant decrease in the velocity of horizontal movements at the end of the aftershock process of the catastrophic Racha earthquake of 1991 on the southern slope of the Greater Caucasus was fully confirmed. Keywords—tectonics; geodynamics; GPS; structure; Earth crust; Greater Caucasus

The article presents the results of a comprehensive study of seismotectonic, geological-geophysical, geodynamic, and seismological data in the region of the Salsk earthquake of May 22, 2001, M = 4.7, in the low-seismic region of the junction of the Scythian Plate and the East European Platform are presented. The parameters of this earthquake source associated with a deep tectonic structure identified by the microseismic sounding method (MSM) are estimated based on seismological and macroseismic data. The MSM section through the region of the Salsk earthquake was obtained by a submeridional profile about 65 km long across the strike of the Manych deflection zone. It was established that the hypocenter of the 2001 Salsk earthquake was confined to the Salsk fault zone included in the system of the Manych faults. This fault is expressed in a section in the form of a narrow subvertical strip with low seismic wave velocities traced from the Earth’s surface to a depth of more than 40 km. Immediately in the area of the earthquake below a depth of 10 km, the recognized fault zone has a local expansion at the point of transition through the plane when the sedimentary cover contacts with the Proterozoic basement. The assessment of the hypocentral position and source mechanism solution (a gently dipping thrust of the northern side at an angle of 25°–33°) correlates well here with the depth and inclination of the surface of the Proterozoic basement, the elements of which are also traced in the MSM section.

Abstract—The results of integrated geological and geophysical studies of active faults and deep structure of the Kerch-Taman region are presented. Data on the deep structure of potential sources of strong earthquakes determining the level of seismic hazard are obtained. Examples of the active faults, well studied on the surface, show that these structures are clearly spotted by microseismic sounding method as the displacements of contrasting layers in the section at a depth of a few km or as narrow low-velocity bodies. In the zones of the Tobechik, South Azov, and Phanagoria faults at depths of 7–12 km, high-velocity isometric inclusions are established. These segments are especially important for making ther repeated MSM measurements for seismic forecasting purposes.

В статье освещены результаты впервые выполненных GPS-измерений вдоль геодезического профиля, пересекающего все основные геологические структуры в Осетинском регионе Большого Кавказа. Интерпретация результатов измерений выполнена в сопоставлении с результатами неотектонических исследований и данными о глубинном строении. Максимальное уменьшение современных скоростей поперечного сжатия зафиксировано в области наивысшего подъема к земной поверхности низкодобротного объема земной коры, оказывающего распирающее действие на все горное сооружение. Наличие значимых поперечных смещений поверхности отражает сдвиговую составляющую по крупнейшим разломам кавказского простирания. Полностью подтвердилось прогнозированное ранее существенное снижение скорости горизонтальных движений по окончании афтершокового процесса катастрофического Рачинского землетрясения 1991 г. на южном склоне Большого Кавказа. The article highlights the results of the first performed GPS-measurements along the geodetic profile crossing all the main geological structures in the Ossetian region of the greater Caucasus.The interpretation of the measurement results was performed in comparison with the results of neotectonic studies and data on the deep structure.The maximum decrease in the current transverse velocity of compression rates is recorded in the area of the highest rise to the earth's surface of the low quality volume of the earth's crust, which has a bursting effect on the entire mountain structure.The presence of significant transverse displacements of the surface reflects the shear component along the largest faults of the Caucasian strike.The previously predicted significant decrease in the rate of horizontal movements at the end of the aftershock process of the catastrophic Racha earthquake of 1991 on the southern slope of the greater Caucasus was fully confirmed.