Preliminary estimates of plate convergence in the Caucasus Collision Zone from global positioning system measurements

Global Positioning System (GPS) measurements (1991–1994) traversing the Greater and Lesser Caucasus mountains indicate a minimum N‐S shortening of 10±2 mm/yr. This represents approximately 30–50% of the NUVEL‐1A convergence rate between the Arabian and Eurasian plates. The remainder of the convergence appears to be accommodated in the areas south of the Lesser Caucasus, by a combination of right‐lateral strike‐slip faulting on planes oriented N 120°E, and shortening on thrust faults with similar orientations. More dense GPS observations conducted in the epicentral area of the April 29, 1991, M s =7.0 Racha, Georgia earthquake, which occurred along the southern boundary fault of the Greater Caucasus mountains, indicate N‐S shortening following the earthquake which we interpret as due to post‐seismic slip. This mechanism may contribute to the substantially lower shortening rates derived from seismic moment tensors compared with tectonic estimates of shortening rates in the Caucasus.