Transverse Faults of the Eastern Caucasus and Their Manifestations in Seismicity

Abstract

The features of the spatial distribution of earthquake sources in the eastern Caucasus (within the borders of Azerbaijan and the Chechen Republic of the Russian Federation) are analyzed. According to the method developed in recent years to identify seismogenic zones of deep faults by manifestations of weak seismicity, transverse faults extending in the diagonal direction (SW−NE) are found. Like other faults that are longitudinal to the strike of the mountain-folded structures of the greater Caucasus, they are characterized by the different level of seismic activity at the different segments. Only their separate segments of short length are seismically active. Transverse faults are deep and intersect the Earth’s crust through all its thickness. Some of them are associated with the sources of destructive earthquakes. For example, the Kurchaloi earthquake with M = 5.6 occurred on the northern slope of the greater Caucasus, in the eastern part of the Chechen Republic in 2008, which caused human losses and destructions. Its source was confined to the deep NE-striking fault, confining the mountain protrusion of the Dagestan wedge from the northwest. The strong seismic events Anapa of 1996 and Lower Kuban’-II of 2002 also took place on the western periclinal of the greater Caucasus, in the area of Anapa transverse flexural-fault zone. The longitudinal tectonic faults (of Caucasus strike) also demonstrate not only weak but also high magnitude seismicity. Such faults were associated with the sources of the strongest earthquakes in the late 20th and early 21st centuries (1970 Dagestan, 1977 Chernogorsk, 1991 Racha, 1992 Barisakho, 2000 Baku, and 2009 Oni). But the transcaucasian disjunctives for a long time have been underestimated as hazardous seismogenic structures, although their activation may lead to serious consequences. This work shows the role of such faults in the distribution of strong and weak seismicity of the region.