Crack Models of Repeating Earthquakes Predict Observed Moment-Recurrence Scaling

Small repeating earthquakes are thought to represent rupture of isolated asperities loaded by surrounding creep. The observed scaling between recurrence interval and seismic moment, $T_r$ ~ $M^{1/ 6}$, contrasts with expectation assuming constant stress drop and no aseismic slip ($T_r$ ~ $M^{1/ 3}$). Here we demonstrate that simple crack models of velocity-weakening asperities embedded in a velocity-strengthening fault predict the $M^{1/ 6}$ scaling; however, the mechanism depends on asperity radius, $R$. For small asperities ( $R\_{\infty} < R < 2R\_{\infty} $, where $R\_{\infty}$ is the nucleation radius) numerical simulations with rate-state friction show interseismic creep penetrating inwards from the edge, with earthquakes nucleating in the center and rupturing the entire asperity. Creep penetration accounts for ~$25\%$ of the slip budget, the nucleation phase takes up a larger fraction of slip. Stress drop increases with increasing $R$; the lack of self-similarity due to the finite nucleation dimension. For $2 R\_{\infty}

Type

Journal article

Publication

Journal of Geophysical Research: Solid Earth, 123