HR: 0830h
AN: T51F-0225    [PDF]
TI: High Resolution Surface Wave Tomography��The Structure of Lithosphere and Dynamics in East Asia and West Pacific Marginal Sea
AU: * Zhu, J
EM: zhujs@cdut.edu.cn
AF: Chengdu University of Technology, ErXian Qiao East No1, Chengdu, 610059 China
AU: Cao, J
EM: Caojm@cdut.edu.cn
AF: Chengdu University of Technology, ErXian Qiao East No1, Chengdu, 610059 China
AU: Yan, Z
EM: yanzq@cdut.edu.cn
AF: Chengdu University of Technology, ErXian Qiao East No1, Chengdu, 610059 China
AB: The continent of East Asia and West Pacific marginal sea was formed by convergence of a series of micro-plates and blocks in the late Paleozoic (about 250-220 Ma). Since Mesozoic (about 150 Ma) the asthenospheric material upwelling caused the lithosphere extension and thinning, and with strong activities of volcano and magma. In Cenozoic the continental margin continued to develop large scale rifts and marginal sea, a series of extending oceanic ridges and basins appeared. In Paleocene epoch the Indian sub-continent collided with the Eurasian continent causing the crust to be shortened and rapidly uplifted, forming the highest of Qinghai-Tibet plateau and the largest convergent region on the Earth. According to approximately 20,000 long-period digital seismic waveforms from 1200 events (7.0�AM�A5.0) recorded by 60 digital seismic stations from CDSN, GSN, GDSN, and GEOSCOPE network in Eurasia and west Pacific regions, about 6,000 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 lithosphere and asthenosphere. The images of shear wave velocity indicate that from upper crust to the depth of 70 km, high velocities are displayed in the region of eastern part of East Asia and West Pacific marginal sea, in contrast, extremely low velocities illustrated in the Qinghai-Tibet Plateau and its surrounding areas. The low velocity anomaly chain is located along the convergence belt of Tethys from Mediterranean Sea, through Turkey, Iran, Himalayan orogens, Burma to Indonesian islands. In general it is divided by a boundary at 110"�E in lateral direction, and divided by depth of 70-85 km in vertical direction, the velocity images show striking differences. The western part mainly features an accumulated and thickened lithosphere caused by collision between India and Eurasia, and the eastern part displays mainly the extending and thinning lithosphere caused by asthenosphere upwelling. The lithosphere in the west part is 100 km thicker than in east part. The shear wave velocity of lithosphere in west is 0.2 km/s to 0.25 km/s higher than in east, the temperature in the bottom of lithosphere in eastern parts is 300��-400�� higher than western parts. There exists a giant low velocity belt in the asthenosphere 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. The characteristics of the low velocity belt is not same with subduction zone in East Pacific, however, it is the same with the Pacific Ocean rise, Atlantic Ocean ridge and Indian Ocean ridge. The tectonic evolution may undergo the following stages. The lithosphere of east edge of Asia was broken up and the asthenosphere upwelling forming the giant rifts system in mid and late Mesozoic. The present trench-islands arc-basin system in West Pacific marginal sea is the results of interaction with Pacific plate, Australian plate and Eurasian plate in Cenozoic.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting