[SSS17-P16] evolution of localized shear texture on a simulated fault surface of quartz rocks during slip-weakening process at a intermediate slip velocity
Keywords:quartz, weakening, structure, amorphous, healing, gouge
All the experiments in this study were conducted using a rotary-shear, intermediate-to high-velocity friction testing machine in Kyoto University. The samples used for the friction experiments were single crystal of quartz (a synthetic crystal). A pair of solid cylinders with a ring-shaped end surface (inner and outer diameter of 5 mm and 25 mm) was cored from the samples. Experiments were carried out at a constant normal stress of 1.5 MPa and a slip velocity of 105 mm/s condition.
As an experimental result, slip-weakening occurred at the initial 0.2–0.3 m of the sliding and the value of friction coefficient dropped from the peak value 0.6 to residual value 0.2. The peak friction showed log(t) healing [Dieterich, 1972]. Whole of the fault surfaces of the specimens were completely covered with white, fine-grained gouges after the experiments. SEM observations showed that 100–300 µm size of plate-like structures had been formed on the surface. The surfaces of these structures were very smooth and flat. These structures were teared from the surface into a shear direction. SEM observations of the fault section revealed that a continuous shear plane had been formed at the center of the fault zone. Along and parallel to this shear plane, approximate 1.5 µm-thick layers had piled up and formed foliation structures. Similarities in size and direction of the planes suggest that these piled layer structures should correspond to the plate-like structures found on the fault surface.
XRD analyses of the fault gouge revealed that amorphization of gouges had already been occurred during the slip-weakening.