HR: 0800h
AN: T21B-0482    [Abstracts]
TI: Frictional Constitutive Parameters for Serpentine Mud from South Chamorro Seamount
AU: * Noda, H
EM: nodahiroyuki@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Oiwake cho, Kitashirakawa, Sakyo ku, Kyoto, 6068502 Japan
AU: * Noda, H
EM: nodahiroyuki@kueps.kyoto-u.ac.jp
AF: Graduate School of Arts and Sciences, Harvard University, 327 Pierce Hall, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Shimamoto, T
EM: shima@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Oiwake cho, Kitashirakawa, Sakyo ku, Kyoto, 6068502 Japan
AU: Ishii, T
EM: ishii@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 1648639 Japan
AB: The lack of great earthquakes in Izu-Ogasawara and Mariana subduction zones may be associated with low-temperature serpentinite (M. Kasahara, 2003). We have thus started experimental studies on fault constitutive properties of serpentinite gouge, using a biaxial frictional testing machine at Kyoto University. Many conically-shaped serpentine seamounts are developed behind those subduction zones. They are consisted mainly of serpentinite mud with clasts of mantle rocks and high-pressure metamorphic rocks. Previous studies imply that the serpentinite is likely to have formed at depths around 30km. We have used serpentine mud, consisted mainly of chrysotile, in the drill core from South Chamorro Seamount (ODP Leg195). Double shear frictional experiments have been conducted on about 0.3 mm thick gouge at 30 MPa normal stress, at room temperature and under wet conditions (but without pore pressure). A series of velocity-step tests were performed in velocity range from 0.015 to 150 μm/s. Rate-and-state constitutive laws were fit to experimental data, by solving specimen-apparatus interaction numerically searching for the optimum constitutive parameters. Determination of stiffness of the apparatus is essential for accurate estimate of constitutive parameters. Careful measurements have revealed that the total stiffness (9.00×10⁷ N/m) fluctuates by up to about 10 % probably owing to loose alignment of machine elements. This induces errors in constitutive parameters depending on d_c}. If d_c is in the order of 10 μm or larger, the error in b value is in the order of percent or less. But if the d_c is around 1 μm, it becomes tens of percents or larger. The absolute value of frictional coefficient is around 0.2, very low and consistent with that of pure chrysotile (Moore et al., 1997). a- σb value is about 0.005 for velocity steps at 0.015-0.15 μm/s, decreases with increasing slip rate down to about -0.01 for the velocity steps at 15-150 μm/s. It changes from positive to negative at around 10 μm/s. Positive a- σb at low slip rate may explain the aseismicity of the Mariana subduction zone. Transient portion of experimental data on a velocity step can be fit well with the constitutive law with 2 staate variables, except for velocity steps at low slip rate regime (0.015-0.15 μm/s). a value is around 0.0029 and independent of slip rate. {/it σb} value changes from 0.0013 for velocity steps at 0.15-1.5 μm/s to 0.012 for ones at 15-150 μm/s. d_c increases with slip rate from 15 μm for velocity steps 0.15-1.5 μm/s up to 0.6mm for ones 15-150 μm/s. A peak on a velocity step disappears in the velocity steps between 0.015 æm/s and 0.15 æm/s. Reinen et al. (1994) explained this by `two mechanisms model'. In their model for chrysotile gouge, the a- σb value in the frictional law is positive, and it doesn't seem applicable in the higher velocity regime. The change in frictional coefficient at low slip rate seems much more gradual than expected by this model, so that we may need an extra transient term in the flow law.
DE: 3036 Ocean drilling
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005