Seismic Mapping of Crustal and Mantle Deformation beneath the SE Tibetan Plateau with Receiver Function and SKS Splitting Data

Abstract:

The SE margin of the Tibetan plateau is characterized by complex Cenozoic structures created during the India-Asia collision since ~50 Ma. Details on the uplift and deformation, especially those inside the lower crust and upper mantle are still debated. Seismic anisotropy measured from SKS splitting data has been combined with surface GPS data to determine whether the crust and upper mantle beneath the margin have coherent deformation. Due to the poor depth resolution of the SKS data, it is still difficult to constrain the distribution of crustal and upper mantle anisotropy separately with the combined dataset. In this study we used the receiver function to measure crustal anisotropy and combined it with SKS splitting data to determine the anisotropy within the upper mantle. We applied this technique to 80 permanent broadband stations in the area operated by the China Earthquake Administration (CEA). The receiver function data indicate that the crust beneath the plateau possesses a strong azimuthal anisotropic component, with measured delay time varying from 0.50 to 0.90 s. To constrain mantle anisotropy with SKS data, we first correct the waveform distortion induced by crustal anisotropy, and then use them to estimate the splitting parameters. The splitting time measured from the corrected SKS data varies from 0.45 to 0.95 s with rather complicated lateral distribution. These results will be further compared with numerical data to better constrain the deformation mechanism of the area.