5:15 PM - 6:30 PM
[SSS08-P07] Friction and wear properties of Indian sandstone at subseismic slip rates
A thickness of fault zone has a positive correlation with the cumulative displacement, and therefore it can provide us crucial information related to the growth and activity of the fault. However, Shipton et al. (2006) have reported that the growth rate of thickness of fault zones developed within sandstone is significantly lower than that within other types of rock. Hirose et al. (2012) suggested that the low growth rate of the sandstone is derived from a shiny slickenside formed on the fault surface based on their experimental results using calcareous sandstone. However, the friction and wear properties of sandstone should depend on the geological settings such as main constituent minerals, grain size, and formation process. Therefore, it is necessary to investigate those properties with various types of sandstone.
For this purpose, we systematically measured the friction coefficients and the ware rate of white sandstone collected at Karauli, Rajasthan in India (hereinafter, “Indian sandstone”) using a rotary shear friction apparatus (Mizoguchi and Fukuyama, 2010). Friction experiments were performed on a pair of about 40 mm long hollow-cylindrical specimens with the outer and inner diameters of 40 and 16 mm, respectively, under the condition of room humidity and room temperature. We conducted 14 experiments at the subseismic slip rates between 1.2×10-3 and 8.8×10-2 m/s at normal stress of 0.56 MPa. To obtain the steady-state friction coefficients, we averaged the friction coefficients at the slip displacements between 60 and 100 m (μave), following Mizoguchi and Fukuyama (2010). The axial displacement (shortening) is measured to estimate the wear rate. We also monitored temperature at the outer rim of the sliding surface using a radiation thermometer (Keyence, IT2-02, IT2-50).
Our experimental results show that μave is ~0.5 at the slip rates on the order of 10-3 m/s. When the slip rate exceeds 10-2m/s, μave starts decreasing down to ~0.2 with the increase of the slip rate. Although the measurement of axial displacement did not show any significant change during a single experiment, we could estimate a very low wear rate of 6.9×10-2 µm/m by calculating the ratio of change in the sum of axial displacement to the total slip displacement over 14 experiments. We visibly observed the sliding surface after each experiment and found that a shiny slickenside was formed under all experimental conditions. Hirose et al. (2012) reported that the wear rate of calcareous sandstone is high at low slip rate, while it is suppressed at high slip rate due to the formation of shiny slickenside surface. The remarkably low wear rate of Indian sandstone should be attributed to the fact that the shiny slickenside surface was easily formed at any slip rates used in this study.
Our results indicate that the friction coefficient of Indian sandstone is clearly lower than that of calcareous sandstone (Hirose et al., 2012) at the subseismic slip rates. Di Toro et al. (2004) reported that quartzite has a very low friction coefficient even at low slip rates due to the silica gel lubrication. Since ~70% of the constituent minerals of Indian sandstone is quartz, we suggest that the low friction coefficient observed in this study is also caused by the silica gel lubrication.
For this purpose, we systematically measured the friction coefficients and the ware rate of white sandstone collected at Karauli, Rajasthan in India (hereinafter, “Indian sandstone”) using a rotary shear friction apparatus (Mizoguchi and Fukuyama, 2010). Friction experiments were performed on a pair of about 40 mm long hollow-cylindrical specimens with the outer and inner diameters of 40 and 16 mm, respectively, under the condition of room humidity and room temperature. We conducted 14 experiments at the subseismic slip rates between 1.2×10-3 and 8.8×10-2 m/s at normal stress of 0.56 MPa. To obtain the steady-state friction coefficients, we averaged the friction coefficients at the slip displacements between 60 and 100 m (μave), following Mizoguchi and Fukuyama (2010). The axial displacement (shortening) is measured to estimate the wear rate. We also monitored temperature at the outer rim of the sliding surface using a radiation thermometer (Keyence, IT2-02, IT2-50).
Our experimental results show that μave is ~0.5 at the slip rates on the order of 10-3 m/s. When the slip rate exceeds 10-2m/s, μave starts decreasing down to ~0.2 with the increase of the slip rate. Although the measurement of axial displacement did not show any significant change during a single experiment, we could estimate a very low wear rate of 6.9×10-2 µm/m by calculating the ratio of change in the sum of axial displacement to the total slip displacement over 14 experiments. We visibly observed the sliding surface after each experiment and found that a shiny slickenside was formed under all experimental conditions. Hirose et al. (2012) reported that the wear rate of calcareous sandstone is high at low slip rate, while it is suppressed at high slip rate due to the formation of shiny slickenside surface. The remarkably low wear rate of Indian sandstone should be attributed to the fact that the shiny slickenside surface was easily formed at any slip rates used in this study.
Our results indicate that the friction coefficient of Indian sandstone is clearly lower than that of calcareous sandstone (Hirose et al., 2012) at the subseismic slip rates. Di Toro et al. (2004) reported that quartzite has a very low friction coefficient even at low slip rates due to the silica gel lubrication. Since ~70% of the constituent minerals of Indian sandstone is quartz, we suggest that the low friction coefficient observed in this study is also caused by the silica gel lubrication.