Late Cenozoic tectonic stresses and focal mechanism of some of the largest earthquakes of the Tien-Shan region

Abstract

This article summarizes field studies of morphometric features of crack systems, kinematic and dynamic data of fault zones and discrete faults, the fault slip data set of epicentral zones of strong earthquakes of Tien-Shan–Suusamyr (1992, М=7.3), Tavaksay (1977, М=5.2), and Karatag (1907, М=7.0, 7.2, 7.3, 6.2). Average and local directions of tectonic stress axes were reconstructed based on geologic and structural data. The structural-dynamic architecture of crustal blocks in epicentral zones was also compiled. Comparative analysis shows that in the entire area studied, the regional stress field is characterized by the NW orientation of the maximal compression axis, NE orientation of the minimal compression axis, i.e., the relative tension. Different mechanisms of shear deformations (i.e., the opposite directions of the offsets) coexist under the same stress field within the Suusamyrtau and Karzhantau areas. The influence of the Talass-Fergana shear zone is clearly revealed here. An alternation of compression and tension domains was observed within the Gissar area. Similar stress field diagrams were noticed for the various earthquake epicenter areas, which were identified using structural geology data, and earthquake focal mechanism studies through seismologic data. The methods used allow the forecasting of the epicentral mechanism based on field data collected during tectonic studies in areas exposed to seismic hazard.