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Abstract

Tethyan oceanic subduction, terrane accretion and continental collision of the Indian and Eurasian plates since 50Ma ago lead to the current Himalayan orogen. As imagined from geophysical data, the deep structure and anisotropy of the lithosphere-asthenosphere system provides important clues in understanding the modality of the orogenic convergence and collision. Based on the seismic data from CENC, IRIS and ISC, using surface wave tomography, we calculated the group velocity. Base on Metropolis rule, we improved the simulated annealing algorithm to simultaneously inverse the velocities and thicknesses and identified the Moho depth and the bottom of lithosphere. We computed receiver functions at permanent and portables stations to provide constrains for crustal deformation. A harmonic analysis was employed to investigate the accurate crustal anisotropy. Crustal shortening and thickening should have occurred beneath the study region. Its partial melting might have enhanced the crustal anisotropy and promoted the accumulation and release of strain. The Himalayan block (HM) is covered by a high velocity anomsaly of about 5% indicating a relatively thin asthenosphere with high velocity. The Vs models demonstrate the leading edge of the subducting Indian slab reaches up to Bangong-Nujiang suture belt (BNS). It indicated that the crust with the thickness of about 65 km in HM and the lithosphere ( ~160 km). The epicenters in HM is relatively deeper than that northern BNS, more deep focus earthquakes are located in the uppermost mantle. The study is supported by the Chinese National Science Foundation (41774069).