Deep structure and volcanic activity of Mount Elbrus and a portion of the Elbrus–Tyrnyauz valley: Geological and geophysical data

Doklady Earth Sciences - A microseismic sounding profile was made along the Baksan River valley from the eastern summit of Elbrus volcano to the southern edge of town Tyrnyauz. The geological...     

The structure and contemporary activity of the Intramoesian fault in northeastern Bulgaria obtained through a complex of new geological-geophysical methods

The structure of the Intramoesian fault is studied for the purpose of estimating its contemporary activity. The fault is known in the territory of Romania and Bulgaria, but it is insufficiently studied both from the geological point of view on the surface and from the geophysical point of view, from which the pattern of its deep structure can be inferred. The fault zone is the key structure for the solution of the problem of estimating the seismic hazard of the region, since the latest studies of this territory indicate the existence of traces of relatively young tectonic processes. According to some concepts the Intramoesian fault sets bounds to the tectonic plate, which is subducted under the Carpathian fold system in the region of the Vrancea Mountains. The paper under consideration presents the results of the field study of the southeastern, the Bulgarian, part of the fault with the application of a complex of geological-geomorphological and geophysical methods. On this basis, the structural segmentation of the fault is carried out and the specific features of its intersection with the disjunctives of another structural orientation are inferred. The data, which determine the degree of its geological and seismic activity, are also discussed.     

Deep structure of the Moscow Aulacogene in the western part of Moscow

Geological and geomorphological studies of the Moscow Aulacogene in the western part of Moscow suburbs have been conducted. This deep structure has been studied by microseismic sounding. The resulting section presents the faults which frame the Teplostanskii Graben in the south (Ramenskii or Butovskii, expressed on the surface as a ledge in the relief) and in the north (Pavlovo-Posadskii, being traced on the surface as a series of lineaments and the valley of Setun’ River). The position of the surface Archean-Lower Proterozoic crystalline basement within the limits of the graben and within the limits of buried elevated blocks (Krasnogorskii and Tumsk-Shaturskii) frame it in the north and south, respectively. Additionally, another fault has been identified in the central part of the graben: the Solntsevskii fault, which has a north-western course and which separates the deflection of the basement in two blocks that are sunken in a slightly different degree. The low-velocity horizons of the Riphean-Vendian complex which make up the graben at depths of 2 to 4.5 km have been found. Down to depths of 15 km, as a component of the upper crust, the graben is underlain by a high-velocity material which also forms the upper part of the section of the crystalline basement in the neighboring elevated block. A low-velocity block of the lithosphere is located in the larger (northern) part of the graben deeper (down to 40 km) beneath the zones of Pavlovo-Posadskii and Solntsevskii faults; in the southern part there is a high-velocity block. In the fault zones framing the graben in the north and south, the surface layer and soil displays a flow of juvenile hydrogen and helium which exceeds several tenfold the background values. According to the collected data, the Teplostanskii Graben has roots traceable through the entire crust and penetrating into the upper mantle.     

Simulation of the Rayleigh waves in the proximity of the scattering velocity heterogeneities. Exploring the capabilities of the microseismic sounding method

The interaction between the fundamental mode surface Rayleigh waves and the buried heterogeneities with various sizes and different velocity contrasts was studied on base numerical simulation. The field of surface oscillations in the proximity of the scattering heterogeneities was computed as a function of frequency. The synthetic seismograms were used for numerical simulation of the microseismic sounding technology proposed earlier, implying that the solution of the inverse problem for the structure of the medium containing inclusions can be derived from the information contained in the ambient microseismic field. It is assumed that the depth of the layer to be reconstructed is linked with the frequency of the microseisms by a simple relation with the help of a numerical coefficient equal to 0.4–0.5. The combined results of the simulation of a direct problem together with the simple inverse problem solution show that the microseismic sounding technique ensures adequate estimation of the medium structure. Previously, the technology was based on the experimental data only and was phenomenological in character. Some relations between the velocity parameters of the original model heterogeneities and their reconstructed images were also studied.     

Contemporary Tectonic Movements of the Western Caucasus and the Ciscaucasia Based on Satellite-Geodetic Observations

Geotectonics - 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...     

Velocities of Present-Day Horizontal Movements in the Central Sector of the Greater Caucasus according to GPS Observations and Their Relation to Tectonics and the Deep Structure of the Earth’s Crust

The results of the first GPS measurements along the geophysical profile that intersects all major geological structures of the Osetiya region of the Greater Caucasus are presented. The results of the measurements are interpreted in comparison with those of neotectonic studies and data on the deep structure.     

Microseismic field affected by local geological heterogeneities and microseismic sounding of the medium

Experiments and numerical model studies have shown that heterogeneities of the Earth’s crust distort the spectrum of the low frequency microseismic field, decreasing spectral amplitudes of a specific frequency f at the Earth’s surface over high velocity heterogeneities and increasing them above low velocity heterogeneities. The frequency f is connected with the depth of a heterogeneity H and the velocity of the fundamental mode of Rayleigh waves V _R (f) through the relation H = 0.5 V _R (f)/f. The low frequency microseismic field is considered as the superposition of trains of Rayleigh fundamental modes with different frequency spectra. The paper proposes an experimentally tested technology enabling the determination of the deep structure of complex geological objects using data on the microseismic background field.     

Tilt Observations in the Normal Mode Frequency Band at the Geodynamic Observatory Cueva de los Verdes,Lanzarote

We have conducted observations with the aid of a seismo-tiltmeter station, which is based on the Ostrovsky pendulum and installed at the Geodynamic Observatory Cueva de los Verdes at Lanzarote Island since 1995. In this station the signal is separated into two frequency bands – tidal tilts (from 0 to 5 mHz) and ground oscillations in the frequency range of free Earths normal modes (from 0.2 to 5 mHz). The later band, called accelerometer channel, has additional amplification. We analyzed the background records in the frequency range of Earths free oscillations from August 2000 to September 2001, as well as, Earths normal modes after strong earthquakes. We found several distinctive persistent peaks in the spectra of background oscillations. Both amplitudes of distinguished peaks and noises have seasonal variations. We found that spectra of background oscillations are different in the frequency interval between 1.4 and 2.5 mHz for North- South and East-West components.