10:15 AM - 10:30 AM
[SSS08-12] Rotary shear experiment for understanding frictional behavior of sandstone
Keywords:Friction, Sandstone, Fault mirror
Laboratory experiments are effective for understanding fault slip behavior during earthquakes, but few experiments have been conducted on sandstone. In order to understand the slip behavior of a sandy fault, we conducted rotary shear experiments of sandstone at wide range of slip rates (from 1.0 to 0.001 m/s). We also observed the cross sections and slip surface structures of the sheared samples by optical and electric microscopes. At the experiment of high slip rate (1.0 m/s), frictional coefficient oscillated unsteadily and the slip surface was intensively worn . At the experiment of low slip rate (under 0.1 m/s), frictional coefficient decreased exponentially and fault mirror was developed on the slip surface. Under microscopes, wildly worn surface and many large fragments (~10μm) were observed in the high-slip rate experiment sample. In contrast, mirror-like surface and spherical nanograins (diameter size 100 nm~) were observed in the low-slip rate sample. Roughness amplitude of the fault mirror was nearly same to that of fault mirror in natural fault. Therefore, we would suggest that frictional mechanism of sandy fault is strongly dependent on slip rate. At high slip rate, wearing of slip surface is dominant, and the frictional behavior is unsteady causing from the existence of fragments. At low slip rate, nanograin formation and wearing occurred and then the nanograins fill asperities on the slip surface making fault mirror. The frictional coefficient are relatively low and steady. These differences in mechanisms and the resultant frictional behaviors, depending on slip rate, could contribute to our understanding of rupture propagation and slip behavior along sandy fault such as splay fault in the Nankai Trough.