Active tectonics of Georgia (Caucasus)
|Location||International Geological Congress,oslo 2008|
|Author||Adamia, Shota۱; Sadradze, Nino۲; Tsereteli, Emili۳; Tsereteli, Nino۴; Varazanashvili, Otari۴|
|Holding Date||28 September 2008|
The Caucasus has long time been known as a natural laboratory for studying the kinematics and various tectonic processes associated with lithospheric plate motion. For more than a century of intensive geologic investigations the enormous data concerning all aspects of the geological structure and evolution of this region has been obtained.
Georgia, a part of the Caucasus, situated in the vast zone of Late Alpine continental collision, in its present-day structure represents tectonically-piled collage of South Tethyan, Tethyan and North Tethyan terranes. During the pre-collisional Late Proterozoic - Early Cenozoic stage the region belonged to continuously developing oceanic basin (Tethys) and its continental framing - Africa -Arabian and Eurasian.
Recent geodynamics of the region is largely determined by its position between the still converging Eurasian and Africa-Arabian plates. According to geologic and geodetic data the rate of this convergence is ~ 30mm/y, of which 2/3 are likely to be taken up south of the Lesser Caucasian (Sevan-Akera) ophiolitic suture. The rest of the S/N directed relative plate motion has been accommodated in the Caucasus chiefly by crustal shortening.
As a result of the continuing northward displacement of the Africa-Arabian plate in Oligocene and post-Oligocene time, the region turned into the intracontinental mountain-fold construction. The process of the formation of its present-day structure and relief (high-mountain ranges - fold-thrust belts of the Greater and Lesser Caucasus, the Rioni and Kura intermontane depressions of the Transcaucasia, Neogene-Quaternary volcanic highlands in Southern Georgia and the Greater Caucasus) was especially intensified since Late Miocene (Late Sarmatian, ~7Ma). The postcollisional horizontal shortening of the region have been realized in the region by 3 different ways:
(1) crustal deformation with wide development of compressional structures - folds, thrusts, reverse faults, nappes; (2) warping and displacement of crustal blocks themselves with their uplifting, subsidence, underthrusting beneath each other and (3) lateral escaping.
Present day deformations of the Earth crust of the region condition its high seismicity. Two large devastating earthquakes occurred in the Caucasus in the past 20 years. The first one was the magnitude 6.9 Spitak earthquake on December 7, 1988. The earthquake became widely known due to immense losses it caused - no less than 25,000 people were killed, some 500,000 left homeless, property damaged is estimated about 8 billion USD. Another large seismic event was the magnitude 7,2 Racha earthquake on April 29, 1991. This earthquake, the strongest ever recorded in Georgia took about a hundred human lives and caused great damage and destruction within densely populated areas. The main shock was followed by numerous aftershocks the largest of which occurred on April 29 (M~6,1), May 5 (M~5,4) and June 15 (M~6,2) causing additional damage.