The azimuth-dependent dispersion curve inversion method to extract 3D anisotropic structure and its application to the eastern Tibetan Plateau

An azimuth-dependent dispersion curve inversion (ADDCI) method is applied to Rayleigh waves to extract 3D velocity and azimuthal anisotropy. The synthetic tests show that the ADDCI method is able to extract azimuthal anisotropy at different depths. The errors of the fast propagation direction (FPD) and the magnitude of the anisotropy (MOA) are less than 10° and 1-2%, respectively. The 3D anisotropic model shows large variations in the FPDs and MOAs with depth and blocks; strong contrasts are observed across major faults, and the average MOA in the crust is approximately 3%. The FPDs are positively correlated with the GPS velocity direction and the strikes of regional faults in most of the blocks. The low-velocity zones (LVZs) in the middle to lower crust are widely observed in the Songpan Ganze Terrence, the north Chuan-Dian block, and surprisingly in the Huayingshan thrust and fold belt. The LVZs in the middle crust are also positively correlated with the low-velocity belt in the uppermost mantle. These observations may suggest that large-scale deformation is coupled vertically from the surface to the uppermost mantle. Crust shortening by the pure shearing process, which involves the thrusting and folding of the upper crust and the lateral extrusion of blocks, may be the major mechanism causing the growth of the eastern Tibetan Plateau.