[SSS15-P14] Effects of ambient temperature on the frictional strength and frictional heating of dolerite
Keywords:frictional strength, frictional heating, temperature dependence, dolerite
Frictional properties at intermediate to high slip velocities are essential to understand the earthquake propagation and slip. Coseismic weakening has been observed experimentally at seismic slip velocities for many types of rocks (e.g., Tsutsumi and Shimamoto, 1997; Di Toro et al., 2011). Weakening mechanisms has been controlled by temperature rise including flash heating, melt lubrication or thermal pressurization (e.g., Rice, 2006; Hirose and Shimamoto, 2005). Although the importance of temperature during fault motion are widely recognized, the effects of temperature on frictional properties at intermediate to high velocities remain unknown. We therefore conducted friction experiments at a wide range of temperatures and investigated the effects of temperature on the friction coefficient (µ) and frictional heating.
Experiments were performed on dolerite (Belfast, Northern Ireland) using a rotary shear deformation apparatus at Chiba University. Samples were displaced up to about 20 m at a normal stress of 1 MPa, slip velocities V of 3–300 mm/s, and ambient temperatures Ta of ~20–500oC in an argon atmosphere with an oxygen concentration of 0.3 %. Temperature adjacent to the slip surface Ts was also measured by a thermocouple placed near the slip surface.
At V = 3–30 mm/s, dolerite showed steady-state friction coefficients µss of 0.46–0.54 at Ta = 20–100oC. Whereas at Ta = 200–500oC, µss increased to 0.64–0.71. At V = 100 mm/s, dolerite showed clear velocity-strengthening with µss up to 0.58–0.64 at Ta = 20–100oC, almost constant values with µss = 0.65–0.69 at Ta = 200oC and 300oC, and clear velocity-weakening with µss = 0.45–0.46 at Ta = 400oC and 500oC. At V = 300 mm/s, dolerite showed strong velocity-weakening at all Ta investigated. In addition, slip-weakening distance (Dc) at V = 100 mm/s and 300 mm/s was smaller at higher Ta. Ts increased with increasing V. The amount of Ts increase (ΔTs) due to frictional heating was almost the same at all Ta tested at V = 3–30 mm/s (ΔTs was ~1oC at V = 3 mm/s and ~30oC at V = 30 mm/s). At V = 100 mm/s and 300mm/s, on the other hand, ΔTs was notably smaller at higher Ta. Thus, the frictional properties and frictional heating of dolerite are affected not only by V but also by Ta. Estimations of temperature distribution during experiments based on three-dimensional finite element modeling are also in progress.
Experiments were performed on dolerite (Belfast, Northern Ireland) using a rotary shear deformation apparatus at Chiba University. Samples were displaced up to about 20 m at a normal stress of 1 MPa, slip velocities V of 3–300 mm/s, and ambient temperatures Ta of ~20–500oC in an argon atmosphere with an oxygen concentration of 0.3 %. Temperature adjacent to the slip surface Ts was also measured by a thermocouple placed near the slip surface.
At V = 3–30 mm/s, dolerite showed steady-state friction coefficients µss of 0.46–0.54 at Ta = 20–100oC. Whereas at Ta = 200–500oC, µss increased to 0.64–0.71. At V = 100 mm/s, dolerite showed clear velocity-strengthening with µss up to 0.58–0.64 at Ta = 20–100oC, almost constant values with µss = 0.65–0.69 at Ta = 200oC and 300oC, and clear velocity-weakening with µss = 0.45–0.46 at Ta = 400oC and 500oC. At V = 300 mm/s, dolerite showed strong velocity-weakening at all Ta investigated. In addition, slip-weakening distance (Dc) at V = 100 mm/s and 300 mm/s was smaller at higher Ta. Ts increased with increasing V. The amount of Ts increase (ΔTs) due to frictional heating was almost the same at all Ta tested at V = 3–30 mm/s (ΔTs was ~1oC at V = 3 mm/s and ~30oC at V = 30 mm/s). At V = 100 mm/s and 300mm/s, on the other hand, ΔTs was notably smaller at higher Ta. Thus, the frictional properties and frictional heating of dolerite are affected not only by V but also by Ta. Estimations of temperature distribution during experiments based on three-dimensional finite element modeling are also in progress.