DISTRIBUTION OF CONTEMPORARY EARTH SURFACE’S 2D STRAIN TENSOR IN PAMIR AND TIEN-SHAN COMPUTED BY TRIPLETS OF GPSOBSERVATION POINTS

Abstract

Based on catalogue of velocities of Central Asian GPS network’s observation points we computed a distribution of values of contemporary 2D strain tensor of Earth surface for most part of Pamir and its neighbor tectonic formations and also for parts of Central and Western Tien-Shan. The velocity catalogue was gained as the result of processing data from many years of GPS observations conducted in the framework of field expeditions by Research station of Russian Academy of Sciences in Bishkek. The computation of Earth crust strain was done using data from sets of three or four neighbor GPS points for computation of each single strain tensor value. By matching the results of computations against maps of regional faults and tectonic structures we mark out the most tectonically active areas and describe types of contemporary surface deformations within them. The most rapid deformation within the region of study is shortening with moderate right lateral shift across the Main Pamir Thrust. The northern part of Karakul Graben at Pamir show moderate tectonic activity as transversal (east-west directed) extension. Normal faults in Kongur-Shan (East Pamir Pull-apart) also undergo transversal extension in their northern part. At central and eastern parts of Tajik Depression we observe latitudinal shortening while in zone of conjunction between Tajik Depression and Gissar ridge we have presumably right lateral shift. There is also significant shortening across main tectonic structures of Naryn basin. Area around Toktogul water storage reservoir undergoes longitudinal shortening. At Jumgal and Kochkor basins we have shortening along north-northwest direction as well as longitudinal shortening across Suusamyr basin. Inside Chu basin we clearly observe two latitudinally-elongated zones rapid longitudinal shortening.