Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review

Abstract

The convergence between the Arabian and the Eurasian plates resulted in the development of the Greater Caucasus (GC) and the Lesser Caucasus fold-and-thrust belts, separated across most of their length by the Transcaucasian depression. The whole sub-horizontal shortening of the Caucasus was quantified at hundreds of kilometers and, according to several studies, reached its maximum rate in the Miocene-Pliocene. At present, convergence between the Eurasian and African-Arabian plates is still active, producing widespread deformation within the mountain belt and in surrounding regions, as testified to by seismological, paleoseismological and GPS data. Understanding the active tectonics of the Caucasus is of paramount importance for a better assessment of geohazards, especially seismic hazard. Moreover, there is a major concentration of residents in Tbilisi, the capital of Georgia, hosting 1.2 million citizens, and in Baku, the capital of the Azerbaijan Republic, with over 2.3 million citizens; both cities are located in active tectonic basins at the southern foothills of the GC. Hundreds of rural villages are scattered in the mountain regions, and all were built without taking into consideration antiseismic criteria. All the above shows that the Caucasus and Transcaucasus regions are subject to an extreme seismic hazard and risk. Here, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, structural-geological and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, activeWNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, although swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus.