High-resolution Rayleigh surface wave tomographic imaging of China and adjacent regions and its geodynamic implications

Abstract：Rayleigh surface waves propagating along 10,600 great-circle paths were selected using more than 20,000 long-period waveform records from 106 wide-band digital seismic stations distributed in Eurasia and the Western Pacific, and high-resolution 3D tomographic imaging of the crust and upper mantle in China and its adjacent regions was performed using the inversion of both dispersion analysis and waveform fitting. The high-resolution Rayleigh surface wave tomographic imaging indicates that: from the upper crust to 70 km depth, high velocities are displayed in the eastern part of East Asia and Western Pacific marginal seas, while very low velocities distributed in the western region centering around the Qinghai-Tibet Plateau; from the 100 to 250 km depth, a giant low-velocity anomaly belt ~250 to 400 km wide and ~8000 km long are shown in the eastern part of East Asia and Western Pacific marginal seas; from the 300 to 400 km depth, there is no appreciable velocity difference and high velocities are still displayed from the Tarim block to Yangtze block. There exist significant differences in lithospheric and asthenospheric structure between the eastern and western parts with longitude 110°E as the boundary. The western part is the lithospheric thickening convergent region formed by India-Eurasia collision, whereas the eastern part the lithospheric extension-thinning region arising from upwelling of asthenospheric material (rise of mantle thermal material). Due to the Paleocene India-Eurasia collision and convergence, the Indian lithospheric sheet was subducted beneath the Qinghai-Tibet Plateau at low angles, causing the plateau uplift and crustal thickening; thus the western part became a lithospheric region. In the Mid-Late Mesozoic, the lithosphere beneath the eastern margin of the East Asian continent was disassembled; as a result, the asthenospheric material upwelled and the lithosphere underwent extension and thinning, thus forming a giant low-velocity zone, which later evolved into the East Asian rift system. The present marginal seas and trench-arc-basin system of the Western Pacific was formed by interaction of the Pacific plate, Australian plate and Eurasia plate in the Mid-Late Cenozoic.