HR: 0800h
AN: T51A-1316    [Abstracts]
TI: Stress State Around Chelungpu Fault, Taiwan, Estimated From Boring Core Samples
AU: * YABE, Y
EM: yabe@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6, Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Song, S
EM: srsong@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Wang, C
EM: wangcy@earth.ncu.edu.tw
AF: Department of Earth Sciences and Insititute of Geophysics, National Central University, 300, Jhongda Rd., Chung Li, 32054 Taiwan
AB: Stress state around a fault is one of the most important keys to understand faulting mechanics. For example, the strength of the fault is directly defined from the pre-faulting stress state. Combined with seismic analyses and precise temperature measurements, coseismic energy partition is investigated. A 2000m-depth hole was drilled near the Chelungpu fault, which has slipped for the 1999 Chi-Chi earthquake (M7.7) in Taiwan. The hole is believed to pass the fault at a depth of 1111m. Boring core samples are recovered continuously from the hole. We, then, measured the stresses by applying DRA, AERA and AE methods to the boring core samples to investigate the stress state around the fault. The techniques, we used, are the so-called core methods that are based on the stress memory effects of rocks. Since it should take more than several or several tens years to fix the stress memory of rocks, the estimated stresses in this study can be related to the stress state before the Chi-Chi earthquake. We have measured axial stresses in vertical and 4 horizontal directions at depths of 739m and 1122m. Assuming one of the principal directions is in vertical, we determined the stress states at the depths. At a depth of 739m, the vertical stress (Sv) is 18.19MPa. The maximum (SH) and the minimum (Sh) horizontal stresses are 23.10MPa and 14.19MPa, respectively. At a depth of 1122m, Sv=21.62MPa, SH=33.40MPa, Sh=19.14MPa. The stress states in both depths are strike-slip regime in spite of the 1999 Chi-Chi earthquake was reverse fault event. The reason of this inconsistency is not clear. We need to increase the number of measurement to resolve this.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: Fall Meeting 2005