Rate dependence of AE activity during frictional sliding

A velocity-step test was performed to examine effects of the macroscopic sliding-rate on AE activity during steady-state frictional sliding on a pre-cut fault in a granite sample. Both the amplitude-frequency relation and the number of AE events per unit displacement changed in response to a change in the macroscopic sliding-rate. Both the AE activity and its rate-dependence evolved with sliding. The rate dependence of cumulative seismic energy calculated from the AE activity shows a positive correlation to that of friction coefficient, suggesting that the rate dependence of seismic energy is one of the origins of rate-dependent friction, because the seismic energy is a part of frictional energy-loss. Further, the rate dependence of seismic energy is much larger than that of friction, meaning that a ratio of seismic energy to frictional energy-loss depends on the macroscopic sliding rate.