Analysis of Crustal Anisotropy Beneath the NE Tibetan Plateau Revealed by Receiver Function Data

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The high topography, thick crust and outward growth of the Tibetan plateau are generally believed to be caused by the continuous collision between the Indian plate and the Eurasian plate since ~50 Ma. The northeastern Tibetan plateau as one of main regions where the plateau grows toward outside is an ideal place to study the crustal deformation. Here we estimated receiver functions from the three-component waveform data recorded by 676 broadband seismic stations in the northeast Tibetan plateau. Then Moho depth and Vp/Vs ratio were calculated by the modified H-κ stacking technique, and crustal anisotropy was also measured using the joint inversion scheme. The Moho depth obviously increases with about 30 km from the northeast to the southwest in the study area. The Vp/Vs ratio exhibits significant lateral variation that the lower Vp/Vs ratios are in the Qilian orogeny and Songpan-Ganzi terrane, while the higher Vp/Vs ratios locate in the western Ordos block, Hetao graben and Yinchuan graben. The significant crustal anisotropy suggests that the polarization directions are approximately parallel to the strikes of faults, sutures and surface geologic structures, and the primary cause may be derived from the middle-to-lower crust. By the combination with the GPS velocity, the surface geologic features, the absolute plate motion (APM) and the SKS/SKKS (XKS) and direct S wave splitting, we demonstrated the mechanically crustal deformation and geodynamic implications. We infer that the uniform lithospheric shortening is likely the dominant mechanism for the crustal uplift and thickening beneath the NE margin of the Tibetan plateau based on its low Vp/Vs ratio and distinctly azimuthal anisotropy.

Presenting Author: Xiaoming Xu

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