5:15 PM - 7:15 PM
[SSS10-P26] Preliminary results of shear friction experiments using Shirahama sandstone for the construction of friction wear model
It has been empirically demonstrated that the width of a fault damage zone correlates with the fault length and the cumulative displacement (e.g., Ogata, 1976; Otsuki, 1978). This empirical relationship has been used for evaluating the possible maximum magnitude of earthquakes on the fault. However, it has also been reported that the growth rate of the fault damage zone width relative to the cumulative fault displacement depends on the host rock type (Shipton et al., 2006). Furthermore, some faults were reported to deviate from this empirical correlation (Gomura fault zone, e.g., Matsuda et al., 2004). Therefore, elucidating the physical mechanisms behind this empirical correlation is important for understanding earthquake physics and assessing earthquake hazards. Hirose et al. (2012) conducted rotary shear experiments on calcareous sandstone and suggested that its low wear rate is related to the formation of fault mirror structures on the sliding surface. They also suggested that the low wear rate could account for the low growth rate of the fault zone width in the sandstone. Maeda et al. (2023, JpGU) also conducted rotary shear friction experiments on quartzose sandstone and found that the wear rate of quartzose sandstone is significantly low under the condition that the fault mirror structures are formed on the sliding surface. However, the mechanical conditions under which the fault mirror structures were formed were different for the calcareous sandstone and the quartzose sandstone, probably due to the difference in their mineral compositions. Since the mineral composition of the rock should be an important factor controlling the wearing processes, we investigated the friction and wear properties of Shirahama sandstone, which has a different mineral composition from the two sandstones mentioned above, by conducting the shear friction experiments. In this study, we report the preliminary results.
We prepared cylindrical specimens (diameter: 25 mm, length: 40 mm) from the Shirahama sandstone blocks collected from Wakayama Prefecture, Japan. Shirahama sandstone consists primarily of quartz (22.5%), plagioclase (29.9%), and matrix (36.7%), and is categorized as an arenitic sandstone (e.g., Fujita et al., 2000). All experiments were conducted using the rotary-shear friction apparatus at the National Research Institute for Earth Science and Disaster Resilience, under normal stresses of 0.5-1.2 MPa, equivalent slip velocities of 0.010-0.080 m/s, and slip distance up to approximately 50 m. In this study, we investigated the friction and wear properties against the input work rate (PV-value), which is defined as the product of the normal stress and the slip velocity. We considered the slip distances of 10-50 m to be the steady state and averaged the friction coefficient over that distance to use as a representative value, µave. We also estimated two different wear rates based on axial shortening and the weight of the wear material collected after each experiment.
The results show that µave transitions from higher values of 0.38–0.53 to lower values of 0.30–0.35 at the PV-value of 0.05 MW/m2. The wear rate also exhibits a sudden increase at this critical PV-value. In addition, a ring-shaped fault mirror structure was observed on the sliding surface after the experiments with the PV-value higher than the critical value. This wear property of Shirahama sandstone contrasts with that of quartzose sandstone, whose wear rate remains very low under the conditions of the mirror structure formation (Maeda et al., 2023, JpGU). This inconsistency may also be due to differences in mineral composition.
We prepared cylindrical specimens (diameter: 25 mm, length: 40 mm) from the Shirahama sandstone blocks collected from Wakayama Prefecture, Japan. Shirahama sandstone consists primarily of quartz (22.5%), plagioclase (29.9%), and matrix (36.7%), and is categorized as an arenitic sandstone (e.g., Fujita et al., 2000). All experiments were conducted using the rotary-shear friction apparatus at the National Research Institute for Earth Science and Disaster Resilience, under normal stresses of 0.5-1.2 MPa, equivalent slip velocities of 0.010-0.080 m/s, and slip distance up to approximately 50 m. In this study, we investigated the friction and wear properties against the input work rate (PV-value), which is defined as the product of the normal stress and the slip velocity. We considered the slip distances of 10-50 m to be the steady state and averaged the friction coefficient over that distance to use as a representative value, µave. We also estimated two different wear rates based on axial shortening and the weight of the wear material collected after each experiment.
The results show that µave transitions from higher values of 0.38–0.53 to lower values of 0.30–0.35 at the PV-value of 0.05 MW/m2. The wear rate also exhibits a sudden increase at this critical PV-value. In addition, a ring-shaped fault mirror structure was observed on the sliding surface after the experiments with the PV-value higher than the critical value. This wear property of Shirahama sandstone contrasts with that of quartzose sandstone, whose wear rate remains very low under the conditions of the mirror structure formation (Maeda et al., 2023, JpGU). This inconsistency may also be due to differences in mineral composition.