Tectonic Implications of Seismic Anisotropy Layering Beneath the Southern Tibetan Plateau Revealed by Integrated Shear Wave Splitting and Receiver Function Analyses.

To investigate continental dynamics underneath the south‐central Tibetan plateau, which composes the Himalayan, Lhasa, and Qiangtang blocks, we have conducted comprehensive examinations of seismic azimuthal anisotropy in the crust using receiver functions (RFs) and crustal and mantle anisotropy using teleseismic shear wave splitting (SWS) analysis. In the Qiangtang block, the observed predominantly E‐W fast orientations from RF and SWS analyses with similar magnitude are interpreted as resulting from eastward crustal flow with minor contributions from the mantle. In the Lhasa block, the crustal anisotropy is approximately N‐S oriented, which is parallel to the strike of rift basins and southward crustal flow. Anisotropy revealed by SWS demonstrates a rotation from E‐W in the north to NE‐SW in the south, which can be interpreted as reflecting mantle flow field induced by the northward movement of the subducting Indian plate. The addition of PKS and SKKS measurements and extension of epicentral distance range to 171.8° for SWS analysis revealed dominantly strong E‐W oriented anisotropy in most parts of the Himalayan block, where most previous studies reported pervasively null measurements. The absence of azimuthal anisotropy is observed in two regions in the Himalayan block which is attributable to mantle upwelling through a previously identified slab window. A two‐layered anisotropy structure with different fast orientations for the upper and lower layers can be constrained in the southern Qiangtang and the vicinity of the Main Boundary Thrust. Plain Language Summary: In our study exploring the underground dynamics beneath the south‐central Tibetan plateau, an area encompassing the Himalayan, Lhasa, and Qiangtang blocks, we utilized advanced seismic techniques to uncover the structure and dynamics of the earth's crust and mantle. In the Qiangtang region, our findings suggest an eastward crustal movement with minimal mantle influence. In the Lhasa block, the observed crustal anisotropy aligns with rift basins with a reduced magnitude, indicating a smaller‐scale southward flow. In the same area, we also observed a transition in mantle flow patterns from east‐west in the north to northeast‐southwest in the south, attributed to the northward movement of the Indian plate. Contrary to previous studies that mostly found no anisotropy in the Himalayan block, our research detected strong anisotropy with east‐west orientations. In two areas of the Himalayan block, the absence of anisotropy likely results from molten rock rising through a gap in the Indian plate. Moreover, we discovered a two‐layered structure of rock alignment near the Main Boundary Thrust and the Qiangtang block. Key Points: Significant anisotropy is revealed in the Himalayan block, where previous studies suggest pervasively null measurementsThe crust significantly impacts observed anisotropy in teleseismic shear wave splitting, potentially leading to double‐layered anisotropyAsthenospheric upwelling through a slab window beneath the Himalayan block accounts for the pervasive null measurements [ABSTRACT FROM AUTHOR]