Internal Deformation of Lithosphere Beneath Central Tibet

We use a large number of high-quality P wave arrival time data recorded by the Hi-CLIMB project to determine a 3-D model of azimuthal anisotropy tomography beneath central Tibet. In the Himalayan block, variations of fast velocity orientation (FVO) are revealed from the crust to the upper mantle. In contrast, the FVO in the Lhasa block exhibits only a slight difference between the lower crust and upper mantle, reflecting a coherent deformation there. Different FVOs are revealed near the Bangong-Nujiang suture, which may reflect anisotropies in different parts of the underthrusting Indian plate. In the upper mantle beneath the Qiangtang block, a strong anisotropy is revealed in the shallower part, whereas a weak anisotropy appears in the deeper part, suggesting that a two-layer anisotropy model is applicable there. A layered lithosphere is detected in the eastern part of the Lhasa block, whereas a consistent FVO is revealed in its western part. Our results indicate that strong deformation has occurred in both the Indian and Eurasian lithospheres.