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.     

Model of the Deep Structure of the Elbrus Volcano in the Light of New Geophysical Data

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.

     

The correlation between the characteristics of seismic wave propagation in Western Caucasus and the geological–tectonic features of the region

The relationship between the characteristics of seismic waves in the Western Caucasus and the geological-tectonic structure of the region is studied for identifying the specificity of seismic propagation in the mountainous regions with a complicated geological structure and forecasting the characteristics of the propagation from the geological and tectonic data. The interpretation is presented for the estimates of the Q-factor of the medium (Q(f) ~ 55f^0.9 in the region of Sochi and Q(f) ~ 90f^0.7 in the region of Anapa), seismic wave enhancement in the upper crustal layers (A(f) ~ 1), and peak ground acceleration residuals, which were previously determined from the records of the local earthquakes and show the distributions of local variations in the parameters of seismic wave radiation and propagation. The obtained characteristics are interpreted in the context of the up-to-date information about the tectonic, geological, and deep structure of the epicentral zones in the Western Caucasus and neighboring territory of the Black Sea. The discrepancies revealed in the low-frequency behavior of the Q-factor in the vicinities of Sochi and Anapa is accounted for by the spatial scale and character of tectonic dislocations of the rocks in these regions. The local variations in the parameters of seismic radiation and propagation are probably related to the geological features of the region such as the fault structures, including the thrusts, shatter zones, oblique seismic boundaries, variations in the thickness and consolidation of the sedimentary cover, as well as the peculiarities in the structure and material composition of the basement.     

Holocenic Geological and Seismic Activity of the Fault System in Northeastern Bulgaria by the Complex of Geological-Geomorphological and Archeoseismological Methods

Izvestiya, Atmospheric and Oceanic Physics - The structure of the fault system of northeastern Bulgaria and, in particular, of the Intramoesian fault, is examined in order to assess their current...