Seismicity, Tectonics, and GPS Geodynamics of the Caucasus

The style of the seismotectonic deformation of the Earth’s crust in the Caucasus and its immediate surroundings corresponds to the thrust setting with a subhorizontal principal compression axis oriented north-northeast across the strike of the Caucasian structures and a subvertical principal extension axis, as established by the reconstruction of a representative set of focal mechanisms of earthquakes. Overall, this deformation style quite closely agrees with the notions developed in plate tectonics according to which the Caucasian segment of the Alpine–Indonesian mobile belt is experiencing strong transversal (across the strike) narrowing as a result of the convergence of the Arabian and Eurasian lithospheric plates. At the same time, the detailed geodetic measurements conducted in the territory of the Greater Caucasus established the GPS site displacements, testifying to the increase of its width. This widening cannot be attributed to the extension across the strike of this mountainous edifice because the focal mechanism solutions of earthquakes in this territory clearly indicate a setting of compressive stresses across the strike of the geological structures. We suggested interpreting this combination of the geodetic and seismological data by the active growth of the volume (and area) of layered rocks of the Greater Caucasus and the emergence of the setting of outward pressure probably as a result of the inflow of the additional mineral material carried by the ascending deep fluids.