High resolution receiver function imaging of the seismic velocity discontinuities in the crust and upper mantle beneath eastern margin of Tibetan Plateau

Abstract:

The collision between Indian and Eurasian plates started about 50 Ma has resulted in intense deformation and crustal shortening in the Tibetan Plateau. Though studied with decades, the mechanism of deformation and southeastward expansion of the Tibetan Plateau remain controversial. As the tectonic transitional zone between the uplifting Tibetan Plateau and the Yangtze block, the eastern margin of the Tibetan Plateau is of particular interest. In past 10 years, several large scale dense seismic arrays were deployed in the eastern Tibetan Plateau with an average inter-station distance about 35km. We collected the seismic data of these densely deployed seismic arrays and the permanent seismic network in the eastern margin of the Tibetan Plateau, and obtained more than 300,000 high quality teleseismic Ps receiver functions. We have obtained high-resolution topographies of the Moho and upper mantle discontinuities beneath the eastern Tibetan Plateau by using receiver function common conversion points stacking technique. The results show a strong lateral variation of the crustal thickness, the depths of 410km and 660km seismic velocity discontinuities, and the thickness of upper mantle transitional zone in this region. Although the depth of the upper mantle discontinuities beneath Sichuan basin is similar to that of the average earth model, the thickness of the upper mantle transitional zone in the southeastern margin of the Tibetan Plateau is about 30km thicker. The lateral variation of the thickness of upper mantle transitional zone in the region may be related to the subduction process of the India plate. The spatial distribution of the velocity discontinuities has a good correlation with surface tectonic structure, indicating the upper mantle dynamic process has great inference on the crustal deformation and shortening in eastern margin of Tibetan Plateau.