Mantle Flow and Fault Zone Related Seismic Anisotropy Revealed by a Dense Linear Broadband Array in Southeast Tibet

Abstract

Southeast Tibet, a key region for the southeastward extrusion of the Tibetan Plateau, remains debated in terms of its tectonic deformation in response to the ongoing collision between the Indian and Eurasian plates. In this study, we applied shear-wave splitting analysis of core-refracted phases recorded by a newly deployed dense seismic array and six permanent stations to delineate crustal and mantle deformation processes. The observed fast polarization directions are predominantly aligned NNW–SSE, while the splitting delay times vary across four sub-blocks. The anisotropy pattern suggests a dominantly asthenospheric origin, consistent with southeastward-directed mantle flow associated with the extrusion of the Tibetan lithosphere. The splitting delay times are relatively larger near major faults and tectonic boundaries compared to areas farther away, and the fast polarization directions beneath these structures exhibit a moderate rotation toward the fault strike, indicating that such tectonic discontinuities contribute to observable azimuthal anisotropy.