Seismic imaging of the crust and upper mantle under Beijing and surrounding regions

We determined a high-resolution 3D P-wave velocity model of the crust and upper mantle under Beijing and surrounding regions in North China by jointly inverting 48,750 arrival times from 2973 local events and 12,249 relative residuals from 234 teleseismic events recorded by the newly built Capital Seismic Network. Our results show considerable differences in the lithospheric structure down to about 200 km depth between the North China basin, the Taihangshan uplift and the Yanshan uplift, which are the three main tectonic units in the study area. At depths of 50–150 km, a pronounced low-velocity anomaly exists under North China basin and Bohai Bay, and right beneath it a high-velocity anomaly extends down to about 200–300 km depth, suggesting that this area has experienced large-scale lithospheric thinning and lithospheric detachment has occurred. The Taihangshan front fault and the Zhangjiakou-Penglai fault zone may have cut through the crust to lithosphere and they become flimsy tectonic boundaries, and the asthenospheric materials may upwell from the two channels. We consider that the deep and shallow structures beneath this region are closely related to dynamic processes that result from the deep subduction of the Pacific slab and its stagnancy in the mantle transition zone under East Asia.