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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

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 Moldavansky). The microseismic 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 earthquake converted wave method (ECWM). 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. [ABSTRACT FROM AUTHOR]

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 Mw = 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. [ABSTRACT FROM AUTHOR]

Abstract: According to obtained results of profiling by microseismic sounding method along the line in submeridional direction crossing the eastern cone of the Elbrus volcano and a magmatic chamber was found under the Elbrus volcano in the range of depths of 7‒13 km below sea level with horizontal size of ≈ 7 km. At the depths of 18‒40 km, a narrow linear magmatic focus steeply dipping in the southern direction is deduced, its horizontal size in the cross section is ≈5 km underlain by another magmatic focus at the depths of 45‒55 km, penetrating the upper mantle. The found magmatic chamber and earthquake center in the crust section are formed by isometric and linear low-velocity bodies. The sections of two profiles show deep faults correlated with morphological features revealed on the surface. To the south of Tyrnyauz town at the depths of 17‒40 km below sea level, a low-speed steeply sinking in the northern direction linear body was found and interpreted as cool volcanic channel approximately at the size of Elbrus. Having carried out geophysical research we obtained data on 7 ancient earthquakes with magnitude M = 6.5‒7.0 occurred over past 7000 years in the vicinity of the volcano. In that historic period five strong eruptions of Elbrus volcano had happened. We settled the absence of time commonality in activations of volcanism and seismicity. Currently Elbrus volcano is in a phase of deep seismic abate. In 2004‒2017 we have fulfilled geological, geophysical and paleoseismological research that confirms Elbrus is not completely extinct volcano. [ABSTRACT FROM AUTHOR]

A geophysical section by the method of microseismic sounding is obtained along the profile that completely crosses the Elbrus volcano in the area of its eastern summit. The peculiarities of the deep structure and edifice of the Elbrus volcano are revealed. [ABSTRACT FROM AUTHOR]