HR: 1340h
AN: T43B-1332    [Abstracts]
TI: Stress State Change Associated With the Chelungpu Fault in the Vicinity of the TCDP Borehole
AU: * Hung, J
EM: jhhung@ncu.edu.tw
AF: Jih-hao Hung, Institute of Geophysics, National Central University, Jungli, 320, Taiwan
AU: Lin, W
EM: lin@jamstec.go.jp
AF: Weiren Lin, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Tokyo, 237-0061, Japan
AB: The Taiwan Chelungpu Fault Drilling Project (TCDP) drilled two holes, 40-m apart, (hole-A, 2 km and hole-B, 1.35 km deep) penetrating the Chelungpu fault at where large surface displacements (~10 m) were observed in the 1999 Chi-Chi earthquake (Mw 7.6). Judging from various sources of data including continuous geophysical logs and core, the fault zone at log depths of 1109 m in hole-A and 1133 m in hole-B were interpreted to be the Chi-Chi rupture fault at depth (with a dipping angle of 30 degrees). In-situ stress state at the drill site can be inferred from 1) extended leak-off tests, 2) borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs and 3) shear seismic wave anisotropy from DSI logs. Further analyses of stress magnitudes incorporating information of tri-axial rock strength, width of breakouts, and shear stress drop during earthquake allow us to better constrain the possible magnitudes of the current principal horizontal stresses around the fault zone and showing that the current stress state is in strike- slip regime, which indicates the principal stress state has been changed from a reverse-fault regime as a result of slip on the Chelungpu fault.
DE: 1200 GEODESY AND GRAVITY
DE: 7221 Paleoseismology (8036)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8107 Continental neotectonics (8002)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting