Crust and upper mantle deformation mechanism beneath the southeastern Margin of Tibetan Plateau revealed by Shear wave attenuation

The deformation mechanisms of the southeastern margin of the Tibetan Plateau are key to understand the process of continental collision. Although different geodynamic models have been proposed, lack enough geophysical evidence, the mechanism is still under debate. Seismic attenuation, which has a very different dependence on temperature, partial melting, and volatile content than seismic velocity, can provide additional constraints on the rheology of the lithosphere and shed more light on the deformation mechanism. With the data from unprecedented dense ChinArray in the southeastern margin of Tibetan Plateau, we employed the two-plane-wave method to invert the teleseismic Rayleigh waves for shear-wave attenuation and velocity model of the crust and upper mantle. The results show that in the southeastern margin of the Tibetan Plateau, there is a low velocity and strong attenuation (Q ~ 125) layer in the depth range of 20 to 35, implying a relatively soft middle-lower crust. Beneath it is a strong lower crust with high velocity and weak attenuation (Q~200) from 40 to 70 km. In the upper mantle, exists an asthenosphere with strong attenuation (Q ~ 70) and low velocity that extends to the depth of about 200 km. Our results suggest partial melting is probably the cause of the weak middle-lower crust. While a thick and week asthenosphere might also facilitate the mantle deformation in the southeastern margin of the Tibet plateau.