HR: 14:55h
AN: T43D-06    [Abstracts]
TI: Frictional Properties and Permeability of Fault Rocks from Taiwan Chelungpu-fault Drilling Project and Their Implications for High-Velocity Slip Weakening
AU: * Sone, H
EM: hirokisone@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Shimamoto, T
EM: shima@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Noda, H
EM: nadahiroyuki@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Song, S
EM: srsong@ntu.edu.tw
AF: Department of Earth Science, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Ma, K
EM: fong@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central University, No.300, Jhongda Rd., Jhongli, 32001 Taiwan
AU: Hung, J
EM: t260001@cc.ncu.edu.tw
AF: Institute of Geophysics, National Central University, No.300, Jhongda Rd., Jhongli, 32001 Taiwan
AU: Wang, C
EM: wangcy@cc.ncu.edu.tw
AF: Institute of Geophysics, National Central University, No.300, Jhongda Rd., Jhongli, 32001 Taiwan
AB: Taiwan Chelungpu-fault Drilling Project, central Taiwan, has recovered cores from 500 m to 2000 m depth, penetrating several distinct major fault zones with various structural features. Amongst them are 3 fault zones encountered at 1111m, 1153m and 1222m depths, which are close to the estimated depth (1200m) of the Chelungpu fault from field and seismic reflection surveys, and thus are the primary candidates for the fault slip plane of the 1999 Chi-Chi Earthquake. Each fault zone consists of a fault breccia and gouge of 1 - 1.5 m thickness. We have measured hydraulic properties of fault rocks and conducted high-velocity friction experiments using drill core samples to understand the fault motion of the northern part of Chelungpu fault, characterized by high slip rate and large displacement. Gas permeability of the fault rock samples have been measured in an intravessel deformation-fluid-flow apparatus in Kyoto University using a steady-flow method with nitrogen gas for several pore pressure gradients (0.1 - 2.0 MPa) at effective pressures up to 140 MPa. Preliminary results for fault rock samples from the fault zone at 1153m depth show that permeability values range in between 10^-14 to 10^-18 m². By taking in consideration the Klinkenberg Effect for gas permeabilities under various pore pressure gradients, water permeability is expected to be lower by approximately half to a single order of magnitude. Previous numerical analysis on the possible effect of thermal pressurization (Noda et al., 2003) estimates that fault rocks with such permeability values would have little frictional strength reduction (possibly less than 10 %) especially at depth shallow as 1000 m. High velocity frictional experiments have been conducted on clayey fault gouge from the fault zone at 1111m depth at an equivalent slip rate of 1 m/s and at a normal stress of 0.7 MPa, using a high-velocity ring-shear friction apparatus in Kyoto University. The frictional coefficient weakened from an initial peak value of approximately 1.0 to a steady state value around 0.35 with a slip-weakening distance, Dc, of 5 -10 m. We plan to report experimental results at various slip rates and normal stresses. These measurements will be used to conduct analyses of thermal pressurization combined with high-velocity weakening of gouge to infer slip-weakening behaviors of the Chelungpu fault at seismic slip rates.
DE: 5114 Permeability and porosity
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8010 Fractures and faults
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005