Upper-Mantle Anisotropy in the Southeastern Margin of Tibetan Plateau Revealed by Fullwave SKS Splitting Intensity Tomography

The southeastern margin of the Tibetan Plateau has undergone complex deformation since the Cenozoic, resulting in a high level of seismicity and seismic hazard. Knowledge about the seismic anisotropy provides important insight about the deformation mechanism and the regional seismotectonics beneath this tectonically active region. In this study, we conduct fullwave multi-scale tomography to investigate the seismic anisotropy in the southeastern margin of the Tibetan Plateau. Broadband records at 111 permanent stations in the region from 470 teleseismic events are used to obtain 5,216 high-quality SKS splitting intensity (SI) measurements, which are then inverted in conjunction with 3D sensitivity kernels to obtain an anisotropic model with multi-scale resolution. Resolution tests show that our data set recovers anisotropy anomalies reasonably well on the scale of 1 degrees x 1 degrees horizontally and similar to 100 km vertically. Our result suggests that in the southeastern margin of the Tibetan Plateau the deformation in the lithosphere and asthenosphere are decoupled. The anisotropy in the lithosphere varies both laterally and vertically as a result of dynamic interactions of neighboring blocks as well as lithospheric reactivation. The anisotropy in the asthenosphere largely follows the direction of regional absolute plate motion. The SKS splittings observed at the surface are shown to be consistent with the vertical integral of our depth-dependent anisotropy model over lithospheric and asthenospheric depths. The southeastern margin of the Tibetan Plateau has undergone significant deformation since the Cenozoic due to the collision between the Eurasian and Indian plates in the south and interactions with the Yangtze Craton in the east. Knowledge about the upper mantle seismic anisotropy helps us understand the deformation and dynamic evolution. In this study, we conduct fullwave multi-scale anisotropy tomography for the southeastern margin of the Tibetan Plateau using 5,216 high-quality SKS splitting intensity measurements obtained from the broadband records of 470 teleseismic events at 111 stations. Our result shows a decoupling between the lithosphere and asthenosphere deformations in the southeastern margin of the Tibetan Plateau. The anisotropy in the lithosphere varies both laterally and vertically as a result of the dynamic interactions of neighboring blocks as well as lithospheric reactivation. The anisotropy in the asthenosphere is largely parallel to the regional absolute plate motion, and the SKS splitting observed at the surface is the result of vertical integration of the anisotropy effect through the lithosphere and asthenosphere. A 3D shear-wave anisotropy model for the SE margin of the Tibetan Plateau is obtained by fullwave SKS splitting intensity tomography Result shows a decoupling of lithosphere and asthenosphere deformations in the region, but a coupling under Tibetan Plateau Lithospheric anisotropy has a complex pattern, whereas asthenospheric anisotropy follows the absolute plate motion