HR: 0830h
AN: S31E-0798    [PDF]
TI: Three-Dimensional Shear Wave Velocity Structure in the Crust and Upper Mantle of the South China Sea and its Surrounding Area
AU: * Wu, H
EM: wuhh@geps.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300, Jung-Da Road, Chung-Li, 320 Taiwan
AU: Tsai, Y
EM: ybtsai@geps.gep.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300, Jung-Da Road, Chung-Li, 320 Taiwan
AU: Lee, T
EM: t44001@cc.ntnu.edu.tw
AF: Tung-Yi, Lee, Department of Earth Sciences, National Taiwan Normal University, 88, Section 4 Ting-Chou Road, Taipei,, 116 Taiwan
AU: Lo, C
EM: loch@ccms.ntu.edu.tw
AF: Ching-Hwa Lo, Department of Geosciences, National Taiwan University, 1, Section 4 Roosevelt Road, Taipei,, 106 Taiwan
AU: Toan, D
EM: geoins@ncst.ac.vn
AF: Ding-Van Toan, Institute of Geological Sciences, National Center for Natural Sciences and Technology, Hanoi,, 350 Viet Nam
AB: The three-dimensional shear wave velocity structure in the crust and upper mantle of the South China Sea and its surrounding area was investigated with fundamental mode Rayleigh and Love wave group velocities in the periods 14-120 s. The path coverage is good for most of the periods. The group velocity data were inverted for the group velocity distribution maps in the studied area with 2-D tomographic technique without any a priori regionalization. The resolutions of the tomographic analysis were quite decent in most of the target region. The group velocity maps were inverted for the shear wave velocity structure in the crust and upper mantle In the shallow depth, lateral heterogeneities with short wavelength were seen in the group velocity maps. This might be related with complicated surface structures. In the middle depth, the group velocity maps were well correlated to the main tectonic features seen at the surface. The thickness of the lithosphere of the South China Sea Basin is probably 60 km. A high shear wave velocity gradient clearly exists along longitude 105E down to a depth of about 250 km. At shallower depth, the velocities are noticeably higher east of this longitude than west of it. At depth below about 85 km, both east and west of this longitude have comparable velocity distribution. This 105E structure extends southwards to the northeast side of the Red-River Fault Zone in Indochina. The Red-River Fault Zone is probably a fairly deep structure boundary, its northeastern side has higher shear wave velocity than its southwestern side. The extrusion of Indochina, due to India-Asia collision, is probably partly driven by some kind of flow in the upper mantle beneath Indochina and Sunda Shelf. Borneo, Palawan trough, Palawan and most of Sulu Basin have lower shear wave velocity.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
DE: 7220 Oceanic crust
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: 2003 Fall Meeting