Seismic anisotropy of upper mantle in the northeastern margin of the Tibetan Plateau
青藏高原东北缘上地幔各向异性研究

Based on the polarization analysis of teleseismic SKS waveform data recorded at 30 seismic stations in the regional digital seismograph networks of the northeastern margin of the Tibetan Plateau,the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by use of the grid searching method of minimum tangent energy and the stacking analysis method,and then we acquired the image of upper mantle anisotropy in the northeastern margin of the Tibetan Plateau. In the study region,the fast-wave polarization direction is basically in NW-SE direction with a clockwise rotation trend,and the delay time falls into the interval from 0.70 to 1.51 s. The fast-wave polarization direction is consistent with the strike of the major faults in the region. The variation of the fast-wave directions is similar to the variation of the minimum average principal compressional stress directions in the northeast margin of the Tibetan Plateau,and to the variation of GPS velocity directions. The research results imply that the regional tectonic stress field has resulted in deformation and flow of upper mantle material with clockwise rotation,and make the alignment of upper mantle peridotite lattice parallel to the direction of material deformation. The deformation of the crust and upper mantle is possibly vertically coherent deformation.