Shear Wave Splitting At XinJiang Region

The Xinjiang has undergone a complex tectonic evolution, being affected by the collision of Indian and Eurasian that is expected to left some imprints on the crust and mantle. Xinjiang is generally divided into four major tectonic regions:tienshan orogenies, Tarim basin, Junggar basin, and Altai orogenies. This region is and is characterized by the presence of large-scale, NEE-SWW trending thrust faults and associated earthquakes and is a key place for understanding the basic questions of continental dynamics.In this paper, we overviewed the progresses and achievements on the seismic anisotropy. We examined in detail the example of plane waves propagating an anisotropy media with hexagonal symmetry and explained the occurrence of shear wave splitting. We also compared sensitivity and reliability of three basic techniques of shear-wave splitting analysis. Shear wave splitting analyses have been carried out using teleseismic data from broadband digital stations permanently deployed in Xin Jiang region, we determined fast polarization direction ((?)) and delay time (<δt) between the fast and slow waves using both the minimum energy method and rotation-correlation method.Our measurements show that fast directions of teleseismic shear waves beneath the northern Tarim basin, Tien Shan orogenic belt and Altai orogenic belt are generally parallel to the strike of the structure beneath the stations respectively. Delay times vary from 0.8s to 1.8s. All of these are related to shorten of lithosphere caused by the collision between India continent and Eurasia continent. In contrast, weak anisotropy beneath Tarim Basin and Junggar Basin implies that these Basins had not experienced strong deformation since Cambrian. The fast polarization direction near the Altyn fault corresponds to the strike of the fault which implies the fault had cut the whole lithosphere.