Effects of fault roughness on estimating critical slip-weakening distance from fault slip history: A laboratory study

Earthquakes are the dynamic rupture of faults governed by fault weakening processes. Critical slip-weakening distance (D_c) is a crucial source parameter of earthquakes, and the determination of D_c is of great concern to semiologists. However, determining D_c for natural earthquakes is challenging due to the trade-off in inversed source models. To solve this problem, Fukuyama and his coworkers proposed a simple method (denoted as the F&M method) to estimate D_c directly from slip-velocity functions. According to the F&M method, the fault slip at the peak slip velocity (D_c') can be used as an approximation of D_c. However, the feasibility of this method has not been completely resolved. Here, we performed laboratory earthquake rupture experiments to examine the validity of the F&M method. Experiments were conducted on faults with different roughness and stress level. We studied the effect of fault roughness on the validity of the F&M method. Our results show that the increase in fault roughness could complicate the fault weakening process, producing repeated weakening and strengthening phase, which leads to a prominent deviation between D_c' and D_c. Furthermore, we also observed a correlation between the critical slip-weakening distance D_c and the final fault slip D. Such correlation implies the scale-dependent nature of D_c, which is consistent with seismic observations in the field.