Formation process and mechanical property of slickenside

Slickenside is well-known microstructure created on fault surface as a shiny and smooth fault plane. However, its generation process and influence on fault behavior have not been studied in detail so far. In order to understand that, we conducted frictional experiments on Carrara marble using a rotary shear apparatus to produce artificial slickenside. Frictional experiments are performed on hollow and solid cylinders of Carrara marble at normal stress of 1.0, 2.0, 3.0 MPa (with hollow cylinders) and 5.0, 10.0 MPa (with solid cylinders), slip rate of 0.1 m/s, and displacement of up to 5 m. Before starting each experiment, the specimens are rotated at low slip rate (0.01 m/s) and low normal stress (0.3 MPa) to produce parallel and smooth slip surfaces. The results are followings: 1) Slickenside is formed in friction experiments even at low slip rate (0.1 m/s). 2) The slickenside is rather developed at higher normal stress and/or longer displacement conditions. 3) The slickenside is formed only on the ground tiny grains of calcite, which is produced on the slip surface during the initial stage of experiment. 4) The slickenside starts to form after the temperature of slip surface reaches ca. 100°C. 5) The frictional coefficient at lower normal stress such as 1.0, 2.0 and 3.0 MPa, is ca. 0.6, while at higher normal stress it decreases to ca. 0.2 with the development of slickenside. Based on these results, we infer the following formation process of the slickenside. The calcite grains on the slip surface are crushed to tiny powders at the initial stage of experiment. Then the powders are strongly squeezed by shearing and are sintered to form slickenside. This phenomenon is similar to that of tribofilm. The exact normal stress effect on the frictional coefficient is presently under investigation.