Clockwise Rotation of Upper-Mantle Strain and Crust-Mantle Coupling Beneath the Eastern Syntaxis Tibet

AB: We performed shear-wave splitting of core phases using a subset of 33 selected events within an array composed of 48 broadband stations that spans a 650x350 km area crossing the Lhasa and the southern part of the Qiangtang terranes. Our results reveal the presence of azimuthal anisotropy with small-to-moderate delay times (0.5-1.4s). The consistency of the splitting parameters with respect to back-azimuth, as well as the absence of splitting along propagation paths parallel to the symmetry axis, suggest that a single layer of horizontal anisotropy in the lithospheric mantle adequately explains the data at most of our stations. At regional scale, the most striking feature is the remarkable southeastward clockwise rotation of fast polarization axis around the eastern Himalayan syntaxis, a characteristic compatible with geomorphology, structural geology, paleo-magnetism and GPS. At a more local scale, our study region can be divided into various zones based on similarity in the splitting pattern. The most remarkable zone is