Seismic Anisotropy Layering Beneath the South Tibet

Abstract:

To investigate crust and mantle deformation beneath the central Himalayan mountain range and southern Tibetan Plateau resulting from the underplating of the Indian plate, both shear wave splitting and receiver function approaches are utilized to image crust and mantle seismic azimuthal anisotropy. We obtain a total of about 14000 pairs of XKS (including SKS, SKKS, and PKS) shear wave splitting parameters recorded by 229 seismic stations from the Hi-Climb and other experiments. The majority of the splitting results show a systematic variation, from NNW-SSE near the Indus-Yarlong Suture to W-E near the Bangong-Nujian Suture, and to NW-SE in the central Qiangtang Terrane in the north, which are similar to results from previous studies. The existence of azimuthal dependence of the fast polarization orientations from the stations between Indus-Yarlong and Bangong-Nujian suture zones indicates a potential of two-layer anisotropy in the Lhasa Block. A significant number of high-quality shear wave splitting measurements are found in the Himalayan mountain range, where previous studies find pervasive null measurements. In addition, results from P-to-S converted phases from the Moho discontinuity demonstrate that significant anisotropy exists in the crust, which contributes to the seismic anisotropy revealed by the XKS splitting analysis and provides a feasible interpretation for the azimuthal dependence of the XKS splitting parameters unraveled at some of the stations.