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[SCG62-07] Unstable slip and the temperature dependence of dry quartz gouge
Keywords:friction, quartz, RSF law, stick-slip, dry conditions, temperature effect
The presence of aqueous fluids in the crust has been considered to trigger or be associated with the unstable slip of faults [e.g., 1]. Therefore, the distribution of crustal fluids has been explored using magnetotelluric method. However, in some areas, highly conductive regions, which can be interpreted as the presence of fluid, may not be associated with the occurrence of earthquakes [2]. In this study, the frictional stability of dry quartz gouge was examined by conducting double direct shear tests at elevated temperatures to understand the occurrence of earthquakes in dry regions.
Double direct-shear tests were performed using a biaxial frictional machine. Quartz particles dried at 70 °C for 24 hours were sandwiched between gabbro blocks. A normal stress of 10 MPa was applied to the blocks 1 hour before the experiment. The temperatures of the samples were controlled to be 30, 100, 200, 300, and 400 °C. The shear stress was applied by loading the center block . The sliding velocity was controlled to be 0.36, 3.0, and 39 µm/s during the experiments. The displacement, normal stress, and shear stress were recorded to analyze the response in the velocity-step tests. The friction coefficient was calculated as the shear stress divided by the normal stress. The temperature dependence of the constitutive parameters a, b, and a-b of the rate- and state-friction (RSF) law was determined by fitting the change in the friction coefficient to the RSF equation.
The a value did not change with temperature in this temperature range, while the b value increased with increasing temperature. The a-b values were negative at all temperatures and decreased with increasing temperature. Stick-slip occurred at 400 °C. In previous studies, the a-b value of quartz gouge was thought to be negative only in wet conditions, and the presence of fluid was considered essential for slip instability [1]. However, our experiments showed that unstable slip can occur even under dry conditions, particularly at elevated temperatures. We will discuss the mechanism of slip instability in dry quartz gouge.
Reference
[1] Masuda K et al. Effects of frictional properties of quartz and feldspar in the crust on the depth extent of the seismogenic zone. Prog Earth Planet Sci. 2019, 6, 50.
[2] Ichihara H et al. A 3-D electrical resistivity model beneath the focal zone of the 2008 Iwate-Miyagi Nairiku earthquake (M 7.2). Earth Planet Sp. 2014, 66, 50.
Double direct-shear tests were performed using a biaxial frictional machine. Quartz particles dried at 70 °C for 24 hours were sandwiched between gabbro blocks. A normal stress of 10 MPa was applied to the blocks 1 hour before the experiment. The temperatures of the samples were controlled to be 30, 100, 200, 300, and 400 °C. The shear stress was applied by loading the center block . The sliding velocity was controlled to be 0.36, 3.0, and 39 µm/s during the experiments. The displacement, normal stress, and shear stress were recorded to analyze the response in the velocity-step tests. The friction coefficient was calculated as the shear stress divided by the normal stress. The temperature dependence of the constitutive parameters a, b, and a-b of the rate- and state-friction (RSF) law was determined by fitting the change in the friction coefficient to the RSF equation.
The a value did not change with temperature in this temperature range, while the b value increased with increasing temperature. The a-b values were negative at all temperatures and decreased with increasing temperature. Stick-slip occurred at 400 °C. In previous studies, the a-b value of quartz gouge was thought to be negative only in wet conditions, and the presence of fluid was considered essential for slip instability [1]. However, our experiments showed that unstable slip can occur even under dry conditions, particularly at elevated temperatures. We will discuss the mechanism of slip instability in dry quartz gouge.
Reference
[1] Masuda K et al. Effects of frictional properties of quartz and feldspar in the crust on the depth extent of the seismogenic zone. Prog Earth Planet Sci. 2019, 6, 50.
[2] Ichihara H et al. A 3-D electrical resistivity model beneath the focal zone of the 2008 Iwate-Miyagi Nairiku earthquake (M 7.2). Earth Planet Sp. 2014, 66, 50.