HR: 0800h
AN: T11A-0333    [Abstracts]
TI: High velocity frictional properties of clay-bearing fault gouges : experiments and modelling
AU: Brantut, N
EM: brantut@clipper.ens.fr
AF: Laboratoire de Geologie - ENS/CNRS, 24 rue Lhomond, Paris, 75009, France
AU: * Schubnel, A
EM: aschubnel@geologie.ens.fr
AF: Laboratoire de Geologie - ENS/CNRS, 24 rue Lhomond, Paris, 75009, France
AU: Rouzeaud, J
EM: rouzeaud@geologie.ens.fr
AF: Laboratoire de Geologie - ENS/CNRS, 24 rue Lhomond, Paris, 75009, France
AU: Brunet, F
EM: brunet@geologie.ens.fr
AF: Laboratoire de Geologie - ENS/CNRS, 24 rue Lhomond, Paris, 75009, France
AU: Shimamoto, T
EM: shima007@hiroshima-u.ac.jp
AF: Department Of Earth And Planetary Systems Science Hiroshima University, Higashi-Hiroshima 739-8526 Hiroshima, Hiroshima, 739-8526, Japan
AB: The present study focuses on the experimental measurement and theoretical understanding of the high-velocity frictional properties of the MTL (Median Tectonic Line at the Tsukide outcrop, Japan) fault gouge and on its possible consequences on the large scale behaviour of clay bearing fault gouges during co-seismic slip. Several experiments were conducted on the MTL fault gouge using a rotary-shear apparatus at high velocities (up to 1.03 m.s^-1), low normal stresses (up to 1.4 MPa), for displacements up to 60 m. During these experiments, we observed systematically a slip-weakening behaviour, i.e. a dramatic decrease in the coefficient of friction, from a value of ~1.2 to a value of ~0.3. In addition, the slip-weakening distance D_c also decreased with increasing normal stress. Optical and SEM observations show the presence of a very thin slipping zone, with important grainsize reduction. TEM analysis using a FIB section shows that this zone is partially amorpheous, with only a few remaining oxides grains of the order of a few nanometers in grainsize. XRD analysis show that the initial kaolinite content disapeared after shearing, probably due to co-seismic dehydration of kaoliniti into metakaolinite (an amorpheous mineral) and bounded water exsolution. For comparison, additional experiments were conducted under similar conditions on pure kaolinite gouge samples. Monitoring humidity, we did observe a release of water vapor during these experiments. Further, we present a numerical model in which thermal pressurization of pore fluid is coupled to dehydration reactions. Our modellling shows that thermal dehydration of hydrous clay minerals may be a non-negligible phenomenon during co-seismic slip. In well documented fault gouges such as San Andreas, Aegion, or the MTL where the water content can reach up to 10% in weight, pore pressure raise due to frictional exsolution of bonded water may : 1) be at least comparable to the thermal pressurization term, 2) help overcome normal stress and induce damage by hydrofracturation of the fault walls, 3) limit the temperature rise and thus prevent the formation of pseudotachylites.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 5112 Microstructure
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting