High Resolution Surface Wave Tomography in East Asia and West Pacific Marginal Sea

Abstract

AbstractThis paper deals with high resolution surface wave tomography in East Asia andWest Pacific marginal sea (60°E–160°E, 20°S–60°N). According to approximately 12 000 long‐period digital seismic waveforms from 650 events (7.0 ≥ M ≥5.0) recorded by 58 digital seismic stations from CDSN, GSN, GDSN, and GEOSCOPE network in Eurasia and West Pacific regions, 4 400 accurate surface wave dispersion curves with periods ranging from 8 to 250 seconds were selected and employed for inversion. The high resolution 3‐D shear wave velocity images in this area were constructed by inversion of both dispersion and waveform showing a notable lateral variation in the crust and upper mantle.The images of shear wave velocity indicate that from upper crust to the depth of 70 km, high velocities are displayed in the eastern part of East Asia and West Pacific marginal seas, in contrast, extreme low velocities are illustrated in the Qinghai‐Xizang Plateau and its surrounding areas. There exists a boundary of velocity decrease along the Mountain belt from Da‐Hingganling to Taihangshan, Wulinshan, which coincides with the gravity gradient belt in NNE‐SSW trend in East China. The low velocity anomaly chains are located along the convergence belt of Tethys from Mediterranean Sea, through Turkey, Iran, Himalayan orogens, Burma to Indonesian islands.The evolution and geodynamic processes are so different between the eastern part and western part of East Asia and West Pacific marginal seas separated by longitude 110°E. The western part has a thickening convergent lithosphere caused by Indian subcontinent colliding with the Eurasian continent. The eastern part is disassembling causing the lithosphere thinning and extension from asthenospheric material intrusion.