Seismic anisotropy and mantle dynamics beneath China

We analyzed the shear-wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under Mainland China. To obtain reliable results we used three different methods to measure the shear-wave splitting parameters using core phases (SKS, SKKS, SKiKS and PKS) as well as the direct S waves from regional and distant earthquakes. Our results show that the fast orientations of the anisotropy (WNW-ESE) in eastern China are generally consistent with the absolute plate motion (APM) direction of the Eurasian plate, suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice-preferred orientation of olivine due to the shear deformation there. The fast axes in western China generally agree with the strikes of the orogens and active faults, while they are perpendicular to the direction of the maximum horizontal stress, suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear-wave splitting. The fast axes in western China are also consistent with the APM direction, suggesting that the APM-driven anisotropy in the asthenosphere is another source of the shear-wave splitting there. These results suggest that APM-driven anisotropy commonly exists under continents, similar to that under oceanic regions, even though the continental lithosphere has suffered extensive deformation.