HR: 17:30h
AN: T54A-07    [Abstracts]
TI: Average Crust Model and Moho Geometry beneath Taiwan
AU: * Wang, H
EM: apg9005@eq.ccu.edu.tw
AF: Institute of Seismology and Institute of Applied Geophysics, National Chung Cheng University, 168, University Rd., Min-Hsiung, Chia-Yi, Taiwan, Chai-Yi, 621 Taiwan
AU: Chen, H
EM: hwchen@earth.ncu.edu.tw
AF: Department of Earth Sciences and Institute of Geophysics, National Central University, No.300, Jhongda Rd., Jhongli City, Taoyuan County 320, Taiwan, Chung Li, 320 Taiwan
AU: Zhu, L
EM: lupei@eas.slu.edu
AF: Department of Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, Missouri 63103, USA, Saint Louis, 63103 United States
AB: We determine the lateral variation of Moho discontinuity, crust thickness, and Vp/Vs ratios in the vicinity of Taiwan by analyzing all the available broadband teleseismic data collected by BATS (Broadband Array in Taiwan for Seismology, 1998 to 2003) and CWB (Central Weather Bureau, 2002 to 2004). The depth variation of the Moho discontinuity beneath each station is mainly estimated from P-to-Sv converted phase, and later multiples at the lower crust-upper mantle discontinuity show on the radial receiver functions. The average crust model can be obtained by constructing thickness (H)-Vp/Vs ratios (kappa) panel by stacking coherently along apparent slowness (p)-travel time (t) trajectories. The best estimated Moho depth from 41 broadband stations on average is 30 km. The Moho depth varies from north of Taiwan (22 km) and becomes deeper to the south (35 km). The geometry of the Moho across the E-W direction is 30 km at KMNB and gradually becomes steeper with a thickness of 34 km at TPUB. The apparent relatively shallow Moho depth variation for most of the stations and with a profound anomalous thickest Moho beneath SSLB station (52 km) corresponds to a topographic high in the Central Mountain Range. Our results suggest that Taiwan orogeny has probably not reached its isostatic stage. The spatial Moho depth variation is mainly associated with the tectonic evolution and orogeny of Taiwan. Arc-continent collision prefers the existence of possible slab imprints, while arc-arc collision favors it absence. Relatively simple crustal structure beneath two stations, KMNB and MATB, depicts a typical stable and old continental crust with Moho depth at 30 km on average, and the main conversion phases on the radial receiver functions are clear. Lateral velocity structure variations in the Taiwan crust model has an average Vp/Vs ratios of 1.78 (Poisson's ratio of sigma = 0.269), with a higher ratio of 1.85 to 1.87 in TATO and WFSB and anomalous lower ratios in LYUB and YULB, respectively. Receiver functions for other stations in eastern Taiwan are less reliable due to background noise, scattering from crustal heterogeneities, anomalous kappa, and contamination of P-to-S conversions from other intracrustal velocity discontinuities.
DE: 1734 Seismology
DE: 1744 Tectonophysics
DE: 2109 Discontinuities (7811)
DE: 5475 Tectonics (8149)
DE: 8038 Regional crustal structure
SC: Tectonophysics [T]
MN: Fall Meeting 2005