HR: 1340h
AN: T23A-0559    [Abstracts]
TI: Dramatic slip weakening of Nojima fault gouge at high-velocities and its implication for dynamic fault motion
AU: * Mizoguchi, K
EM: mizoguchi@kueps.kyoto-u.ac.jp
AF: Department of Geology and Mineralogy Graduate School of Science,Kyoto University , Kitashirakawa-Oiwake, Sakyo-ku, kyoto, 606-8502 Japan
AU: Shimamoto, T
EM: shima@kueps.kyoto-u.ac.jp
AF: Department of Geology and Mineralogy Graduate School of Science,Kyoto University , Kitashirakawa-Oiwake, Sakyo-ku, kyoto, 606-8502 Japan
AB: The use of Teflon sleeve around simulated gouge between cylindrical specimens has made it possible to perform high-velocity friction experiments on fault gouge, using a rotary-shear high-velocity frictional testing machine in Kyoto [Mizoguchi and Shimamoto, 2002, 2003, 2004]. We present a summary of our experimental data on Nojima fault gouge and demonstrate its significance on seismogenic fault motion. A series of experiments were examined at constant normal stresses of 0.3 to 1.8 MPa and a constant equivalent slip rates of 1.03 m/s [1200rpm], with unconfined and dry conditions. The fault gouge used in the experiments is blue gray gouge derived from granodiorite collected at the Hirabayashi trench along the Nojima fault. The representative mechanical behavior of a simulated fault at the condition, that the normal stress is 0.6 MPa and rotation speed is 1200 rpm, is as follows. At the initiation of a run, friction coefficient rapidly increased to about 0.8 and then decreased gradually. The friction coefficient finally attained to nearly constant [-0.3]. The slip weakening displacement [Dc] to the residual friction was around 30. We also measured temperature of 4 positions in solid-cylindrical granite specimens by using CA thermocouples and then calculated temperature distribution in the specimens numerically to estimate temperature of fault gouge. The results indicate that the maximum temperature of fault gouge during high-velocity friction is around 380 _E#381;. Local temperature in the gouge zone might be higher than the estimated value due to shear localization, but the bulk of the gouge would not melt. Friction and Dc are important parameters to analysis earthquake generation process. The frictional coefficient inferred from the heat flow measurements along the San Andreas Fault was lower than 0.2 and the inconsistent with the laboratory tests confuses many seismologists for a long time [reviewed in Zoback (2000)]. However our results in laboratory suggested that frictional strength of a fault at seismic slip rates might be enough low to explain the low frictional strength of natural faults. As to Dc, there also is a wide difference between laboratory friction test at slow slip rates and seismic wave analysis. The difference is thought to be due to the scaling of fault surface topography. The Dc at low normal stress range from 20 to 40 m and are one order of magnitude larger than the values estimated from seismic wave [Ide and Takeo, 1997; Olsen et al, 1997]. However the Dc at the higher normal stress is the same order of the Dc based on seismic wave analysis. We can explain the inconsistency about the Dc by high-velocity frictional properties of fault gouge. Although weakening mechanism of gouge is unknown at present, our results as well as Goldsby and Tullis (2003) and DiTro et al. (2004) indicate that there is another slip-weakening mechanism enhancing fault instability, in addition to thermal pressurization and frictional melting.
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting