HR: 14:10h
AN: T43D-03    [Abstracts]
TI: Deformation Structures and Physical Properties in the Wells of Chelungpu Fault Drilling, Takeng, West-central Taiwan
AU: * Hung, J
EM: jhung@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300 Jhongda Rod , Jhongli, 320 Taiwan
AU: Wu, Y
EM: u9129500@ncu.edu.tw
AF: Institute of Geophysics, National Central University, 300 Jhongda Rod , Jhongli, 320 Taiwan
AU: Yeh, E
EM: yeh@jamstec.go.jp
AF: JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AB: To understand the physics of the 1999 Chi-Chi earthquake continuously coring and a suit of geophysical measurements were collected in the TCDP drilled holes from depths of 500 to 2003 m (hole-A). The average regional bedding dip, identified from both cores and FMI (or FMS) logs, is about 30 degrees ranging between 20-40 degrees. Nevertheless, the variance of azimuth scattering and increasing or decreasing bedding dips appear across fault zones. A prominent increase of regional bedding dips to 60-80 degrees at depth below 1860 m could be due to structures formed associated with the underlying Changhua fault. Physical properties of formations obtained from wire-line logs are primarily dependent on parameters such as lithology, depth and fault zones. Among 13 fault zones the shallowest one at depth 1111 m, with over 1 m long gouge zone including 12 cm thick indurate black gouge and gradational to breccia and protolith both up and down, is the best candidate for the Chi-Chi earthquake. This fault zone is characterized by: 1) bedding-parallel thrust fault with 20 degree dip; 2) the lowest resistivity (40 percent less than adjacent protolith) caused by highly fracturing in breccia; 3) low density, Vp and Vs, 4) high Vp/Vs ratio (2.4) and Poisson­Ýs ratio (0.4), indicative of high-fluid content weak zone; 5) low energy and velocity anisotropy, and low permeability or fluid mobility within a homogeneous gouge zone; 6) anomalously high CO2 and CH4 content and 7) similar stratigraphic position to the surface ruptures. The fast polarization direction of shear wave is in agreement with an overall azimuth of maximum horizontal stress axis (or bedding dip direction). Locally at depth of 1000-1300 m two sub-stress orientations averaging N20W-S20E and N85W-S85E appear as conjugate minor sets. A rotation of populated fast polarization orientation from NW-SE to NE-SW occurs at depth below 1675 m and could be associated with the high-angle structural dip.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8010 Fractures and faults
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005