Energy partition for grain crushing in quartz gouge during subseismic to seismic fault motion: An experimental study

Brunauer-Emmett-Teller (BET) surface area of quartz gouge was measured before and after shearing deformation at subseismic to seismic slip rates to determine how much of frictional work and fracture energy was consumed during grain crushing. Measurement of BET surface area provides more direct data on surface-area change than grain-size measurement does. Twenty-four experiments on quartz gouge composed of Ottawa sands or crushed quartz were conducted dry (with room humidity) or wet (with added water) at slip rates of 0.006∼1.3 m/s and normal stresses of 0.76∼3.37 MPa, using a high-velocity friction apparatus and a low to high-velocity friction apparatus. About 1 mm-thick gouge was placed between cylindrical specimens of Belfast dolerite of 25 mm in diameter. Results show that grain crushing absorbed only 0.02∼0.22% of frictional work and only 0.05∼1.06% of fracture energy under dry and wet conditions. Thus, grain comminution is unlikely to be an important energy sink at least for mature faults with well-developed slip zone. Surface area of gouge decreases with deformation at seismic slip rates. This and SEM observations suggest partial sintering due to frictional heating. Thus a simple scenario of grain crushing as an energy sink does not hold for estimating the energy budget during earthquakes.