Rayleigh Surface Wave Tomography In Eurasia And West Pacific Areas

This paper deals with the high resolution surface wave tomography in Eurasia and west Pacific areas.1700 events (7.0≥M ≥ 5.0) recorded at 113 digital seismic stations form network in Asia, Europe and west Pacific regions are used in this paper. 9980accurate Rayleigh surface dispersion curves are selected and employed for inversion. The high resolution 3-D shear wave velocity images in this area are constructed by inversion dispersion and show a notable lateral variation in the crust and upper mantle.The images of S wave velocity indicate:1.In 20~40km depth the lithosphere of Eurasia indicates relatively low velocity in opposed the ocean areas exist relatively high velocity.2 The images of S wave velocity indicate that from the upper crust to the depth of 70km, the high velocity is displayed in the region of eastern part of East Asia and West Pacific marginal seas, in contrast, extremely low velocity is in the Qinghai-Xizang plateau and its surrounding areas. There exists a boundary of velocity decrease along the Mountain belt from Da-Xingganling to Taihangshan, Wulinshan, which coincides with the gravity gradient belt in NNE-SSW trend in East China. The low velocity anomaly chain is located along the convergence belt of Tethys from Mediterranean Sea, Turkey, Iran, Himalayan orogens, Burma, Indonesian Islands.3.In 100- 150km depth the upper mantle of the east Eurasia areas and the west Pacific Areas Show a large-scale low velocity.4.There exists a giant low velocity belt in the upper mantle with length of about 8,000 km, width of about 2,500-4,000 km from sea of Okhotsk, Kuril basin, Sea of Japan, North China and South China, South China Sea to Philippine Sea.