Seismic Anisotropy Determined by Shear-Wave Splitting Beneath the Eastern Tibetan Plateau

We monitored shear-wave splitting of SKS phase in global teleseismic data recorded by 36 seismic stations in the eastern Tibetan Plateau (95A degrees-100A degrees E, 31A degrees-36A degrees N) from May to October 2010, to obtain the characteristics of upper-mantle anisotropy beneath the study area. Although the observation duration was short, we had a dense station coverage in the study area and the results are believed valid. The results suggest the presence of moderate to strong seismic anisotropy in the mantle beneath the plateau. The polarization directions of fast shear-wave in the Qiangtang block and the Ganzi-Yushu fault are southeast, which is in agreement with the previous results and the strikes of regional faults. The northeast and southeast trending polarization directions in the Bayan Har block can be explained by the northward movement of the plate. Combining the results of shear-wave splitting in the crust and upper-mantle provides the characteristics of lithospheric deformation. Our results suggest that the crust and upper-mantle in this area have vertically coherent deformation. The delay time is in the range of 0.68-2.31 s which mainly comes from the upper-mantle, suggesting strong anisotropy in the mantle beneath the study area.