Volume 55, Nº 10 (2019)

The formation of fold–thrust dislocations of stratified rocks in the Earth’s crust has been considered as a consequence of the lateral compression of such rocks by converging platforms or lithospheric plates over the last 150 years within the framework of a geosyncline concept and then according to the concept of plate tectonics. Such convergences are reliably confirmed by current geodetic measurements. At the same time there are less popular ideas that present the formation of these dislocations as a result of various local, autonomous processes. The essence of the problem is that the domination of directionally ordered horizontal compression over the value of lithostatic pressure in the Earth’s crust, which is unambiguously determined according to the data of focal mechanisms of earthquakes and in the measurements on stresses in situ in mine workings, makes it necessary to prefer the global mechanism of compression in the form of convergence of horizontally moving lithospheric plates. This convergence is reliably established on a global scale and by modern high-precision geodetic GPS measurements. However, similar GPS measurements, but on regional or local networks rather than on global ones, have shown an opposite result in a few cases. They revealed an increase in the width of representative segments of the mountain belts, rather than a decrease. A detailed study of the geological structure of such areas has indicated that the main role in their formation is played by scaly thrusts, sometimes transforming into small covers, and linear folds and groups of such folds associated with these dislocations and subordinate to them. The formation of such a cover-thrust tectonic structure continues now. For several years, the authors have developed a hypothesis according to which fold–thrust dislocations in the Earth’s crust are formed as a result of an increase in the volume of stratified rocks and as a consequence of an increase in the area of these rocks. They cause volume expansion stresses, similar to the stresses of external compression; crumple; and are dissected by thrusts and reverse faults, tending to cover adjacent territories. It is assumed that the increase in the volume (volume expansion) and the areas of stratified rocks is a result of the entry of additional mineral material with ascending flows of deep mineralized fluids. The increase in the volume and the width of the mountain structure during the formation of its tectonic structure is indirectly confirmed by the near-vertical formations detected in the Earth’s crust in several regions by geophysical methods, which have different velocity characteristics compared to the enclosing environment. These formations can be interpreted as channels of permeability for the penetration of deep fluids—the cause of an increase in rock volume. This suggests that the process of autonomous folding and thrusting in the Earth’s crust really exists in the regional plan, first and foremost, within the mobile mountain belts, along with a global plate-tectonic mechanism.

We have mapped a short-period S-wave attenuation field of in the lithosphere of the Caucasus. We have used a method based on the analysis of the ratio of the maximum amplitudes for S_n- and P_n-waves. We have processed more than 200 earthquakes records, recorded by the Kislovodsk station (KIV) at distances of ~200–750 km. It is shown that, in general, the highest attenuation of shear waves is observed in the western part of the region. It is established that increased and intermediate attenuation takes place for paths simultaneously crossing rupture zones of the 1988 Spitak (M_w = 6.8) and 1991 Racha (M_w = 7.0) earthquakes. At the same time, the source zone of the 1970 Dagestan earthquake with M_w = 6.8 is characterized by mainly lower attenuation. These data are consistent with an earlier conclusion that deep-seated fluids have been ascending into the Earth’s crust from the uppermost mantle for a few decades after large seismic events, and this process leads to a decrease in attenuation of S_n-waves. A high attenuation zone has been identified in the western part of the region, where, according to instrumental and historical data, no seismic events with M ≥ 6.0 have been recorded. It is assumed that processes of a large earthquake preparation may be taking place here.

The discovery of a unique archeological monument of the 6th century AD in the south of Dagestan (the Rubas Fortification) and archeoseismological studies of its military engineering objects have revealed many characteristic deformations caused by previously unknown historical earthquakes. Based on the archeoseismological and geological data, traces of the active fault zone have been found in the area of this archeological monument. The slips on this fault led to the displacement and distortion of the early medieval monumental defensive wall.

The reduction of solar radiation arriving in the summer half of the years by 65° N has been found to be a consequence of decreased inclination of the rotation axis and increased meridional contrast in insolation, rather than a result of climate cooling. Thus, the astronomical climate theory involves a paradox related to the fact that the change in the meridional heat transfer due to a change in the inclination of the rotation axis is disregarded. In this context, the mechanism of the astronomical chronology of climatic events in the Pleistocene needs to be revised.