The Slip Behavior and Source Parameters for Spontaneous Slip Events on Rough Faults Subjected to Slow Tectonic Loading

We study the response to slow tectonic loading of rough faults governed by velocity weakening rate and state friction, using a 2-D plane strain model. Our numerical approach accounts for all stages in the seismic cycle, and in each simulation we model a sequence of two earthquakes or more. We focus on the global behavior of the faults and find that as the roughness amplitude, b_r, increases and the minimum wavelength of roughness decreases, there is a transition from seismic slip to aseismic slip, in which the load on the fault is released by more slip events but with lower slip rate, lower seismic moment per unit length, M_0,1d, and lower average static stress drop on the fault, Δτ_t. Even larger decreases with roughness are observed when these source parameters are estimated only for the dynamic stage of the rupture. For b_r ≤ 0.002, the source parameters M_0,1d and Δτ_t decrease mutually and the relationship between Δτ_t and the average fault strain is similar to that of a smooth fault. For faults with larger values of b_r that are completely ruptured during the slip events, the average fault strain generally decreases more rapidly with roughness than Δτ_t.