HR: 0800h
AN: T51A-1311    [Abstracts]
TI: Distribution of Deformation Features and Clay Mineral Characteristics Around the Chelung-pu Fault, Taiwan
AU: * Hashimoto, Y
EM: hassy@cc.kochi-u.ac.jp
AF: Kochi University, Akebonocyo 2-5-1, Kochi, 7808520 Japan
AU: Nakaya, T
EM: taichin@cc.kochi-u.ac.jp
AF: Kochi University, Akebonocyo 2-5-1, Kochi, 7808520 Japan
AU: Song, S R
EM: srsong@ntu.edu.tw
AF: National Taiwan University, P.O. Box 13-318, Taipei, 106 Taiwan
AB: In 1999, the Chi-Chi earthquake is caused by motion of the Chelung-pu fault striking almost N-S direction.The large slip is concentrated in the northern part of the Chelung-pu fault. The large slip zone is recognized as asperity of earthquake. Taiwan Cheling-pu Fault Drilling Project (TCDP) was conducted in 2004 to penetrate the shallower edge of the asperity. The scientific purpose of this project is to understand materials and conditions of asperity. We focused on the distribution of deformation features such as fault gouge, crack and veins and the characteristics of clay minerals occurred in the fault zone to understand the rock-fluid interaction along fault-fluid system around seismogenic asperity. The candidates for fault zones for the Chelung-pu fault are identified in the depth of 1111m, 1153m, and 1222m. The distribution of deformation features such as fault gouge, cracks and veins were examined. The frequency of fault gouge is concentrated in the 1111m and 1153m zone. At 1222m depth, although frequency of fault gouge is also increased compare to surrounding host rocks, the concentration is smaller than that at 1111m and 1153m. On the other hands, calcite veins are concentrated in the 1222m zone stronger than that in 1111m and 1153m. We analyzed clay minerals by X-ray diffractometer (XRD) after classification of rock types such as sandstone, alteration of sandstone and mudstone, breccia, and gouge around 1111m zone and 1222m zone. The result of XRD analysis shows that most of the samples contain smectite, illite and chlorite in both zones. Total number of iron, or asymmetry of iron between silicate layer and hydroxide layer can be estimated by 002, 003, 004, and 005 reflections of chlorite. The result of examination of the Fe-Mg substitution in chlorite represents that 1) total iron is larger in 1222m host rocks than that in 1111m host rocks, and 2) asymmetry of iron in both layer represents different characteristics in each rock such as 1111m host rocks, 1111m gouge, and 1222m host rocks. Those characteristics in chlorite around fault zone may be controlled by the fluid-rock interaction along fault. The possible factors controlling the clay characteristics are chemistry of fluid, generated heat, or degree in breakage.
DE: 8000 STRUCTURAL GEOLOGY
DE: 8010 Fractures and faults
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005