[S-SS08] Fault Rheology and Earthquake Physics

[SSS08-17] Frictional experiments and numerical simulations for understanding the developing process of composite planar fabrics in faults

*Takeshi Miyamoto¹, Tetsuro Hirono¹, Akari Fuke¹, Satoshi Yukawa¹ (1.Graduate School of Science, Osaka University)

Keywords:friction experiment, numerical simulation, composite planar fabric

Many experimental works have previously performed to understand frictional properties of various kinds of rocks and minerals by using friction apparatus at various orders of sliding velocities ranging from nm/s to m/s. Some of them were conducted together with microscopic observation. However, friction experiments at wide range of velocities on a single type of rock or mineral have been rarely reported. Here we conducted friction experiments using powdered pyroclastic samples at velocities ranging from 0.0002 to 1 m/s, 1.5–3.0 MPa normal stress, and 10 m slip distance under dry and wet conditions. After experiments, we observed the thin sections of sheared samples. We also performed numerical simulation by using discrete element method (DEM) that focused on the changes of distances to adjacent particles (referred as CAP) and forces acting on particles during frictional slip. At higher velocities, the sample showed relatively drastic decrease of friction coefficient and boundary-parallel Y shears. In contrast, R₁ shears, oblique to shear direction, were observed in the samples at lower velocities. Numerical simulations at higher velocities of 0.1 and 1 m/s resulted in slip weakening and development of larger CAP lines parallel to boundary. At lower velocities, larger forces were concentrated locally. These results could imply that the development of composite planar fabrics during frictional slip has a dependency on slip velocity. Although pyroclastic samples we used contain much of volcanic glass, we could not identify the most efficient factor on the development of shear fabrics. Then, we tested frictional experiments using three kinds of quartz powders (supplied from Sigma-Aldrich, Wako, and Thermo Fisher Scientific) at 1 and 0.01 m/s slip rate and 2.0 MPa normal stress under dry condition. We also observed thin sections of sheared samples. At the case of experiment of 1 m/s velocity, friction coefficient was weakened drastically, whereas that of the experiment of 0.01 m/s velocity, it was almost at constant together with development of boundary parallel shear. We will show the preliminary result of friction experiments at wide ranging velocity using quartz supplied from Sigma-Aldrich together with the microscopic observation.