Anisotropic low-velocity lower crust beneath the northeastern margin of Tibetan Plateau: Evidence for crustal channel flow

Detailed seismic structure in the crust beneath the northeastern margin of Tibetan Plateau was revealed by receiver functions of a regional permanent seismic network. At most stations, negative P-to-S converted phases can be detected in the radial receiver functions, prior to the Moho phases, indicating low velocities in the midlower crust. Prominent azimuthal variations in the transverse receiver functions with polarity reversal suggest azimuthal anisotropy in the crust. We used time variations of the P-to-S converted phases at the Moho in the radial receiver functions and the azimuth-weighted stacking of transverse receiver functions to determine the fast direction and magnitude of anisotropy. The low-velocity midlower crust with the coherent azimuthal anisotropy in the northeastern margin of Tibetan Plateau is consistent with the lower crustal channel flow model.