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 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 dataset recovers anisotropy anomalies reasonably well on the scale of 1º x 1º horizontally and ~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 experienced complex deformation since the Cenozoic, resulting in a high level of seismicity and seismic hazard. Knowledge about the seismic anisotropy provides important insight into the deformation mechanism and the regional seismotectonics beneath this tectonically active region. In this study, we conduct a fullwave multi-scale tomography to investigate the seismic anisotropy in the southeastern margin of the Tibetan Plateau. Broadband records from 470 teleseismic events at 111 permanent stations in the region are used to obtain 5,216 high-quality SKS splitting intensity measurements, which are then inverted in conjunction with 3D sensitivity kernels to obtain the anisotropic model for the region with a multi-scale resolution. Resolution tests show that our dataset recovers anisotropy anomalies reasonably well on the scale of 1º x 1º horizontally and ~100 km vertically. Our result suggests that in the southeastern margin of the Tibetan Plateau the deformations in the lithosphere and asthenosphere are decoupled. 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 largely follows the direction of regional absolute plate motion, i.e. southeastward under the Songpan-Ganzi Terrane and the Yangtze Craton and nearly east-west south of 26ºN latitude. The SKS splitting observed at the surface can be interpreted as the vertical integration of the contributions from lithosphere and asthenosphere.