EARTHQUAKE FAULT PLANE SOLUTION AND ACTIVE TECTONICS OF GEORGIA

Recent geodynamics of Georgia and adjacent territories of the Black Sea-Caspain Sea region, as a whole, are determined by its position between the still-converging Eurasian and Africa-Arabian plates.

A map (scale 1:500,000) and a catalogue compiling the seismoactive structures of the region, based on geological and tectonic maps of corresponding scale, seismologic, geodetic (GPS-measurements) and geomorphological data have been established.

Seismoactive structures are identified on the basis of the correlation between neo-tectonic structures of the region and earthquakes.

Active deformation in the region is largely determined by the wedge-shaped rigid Arabian block indenting the region. Sub-meridional compression reaches its climax within the central segment of the Caucasus, along a line running through the central part of the Transcaucasus. It is known that this stripe represents the watershed between the Black Sea and Southern Caspian Sea basins. Westward of this stripe, we observe extension induced by the escape of Central Anatolia, implying that the territory of the Black Sea is not undergoing sub-meridional compression. The deformation is also observed east of the stripe of maximal compression: at the territory of South Georgia and adjoining regions. The maximum stress from the central segments of Caucasus is attenuated differently towards east and west. Hence the eastern and western parts of Georgia are under different tectonic stress regime influencing the geometry and kinematic of the active faults. This is confirmed by the earthquake epicenters and their fault plane solution (FPS), in agreement with the maximum horizontal stress directions obtained by a stress inversion technic from earthquake fault plane solution. Slip directions obtained from FPS are in good agreements with GPS data.

A detailed study was done for Tbilisi area: Serial geological cross-sections, seismic refection profiles, wells, and earthquakes reveal the presence of an active blind-thrust fault beneath Tbilisi. 2D and 3D structural models show that Tbilisi earthquake related to a north-vergent thrust, the historical Mtskheta earthquake may be related north-vergent thrust or backthrust. Empirical relations between fault rupture area and magnitude suggest that these fault segments could generate earthquakes of Mw ~6.5.