Exciting news! We're transitioning to the Statewide California Earthquake Center. Our new website is under construction, but we'll continue using this website for SCEC business in the meantime. We're also archiving the Southern Center site to preserve its rich history. A new and improved platform is coming soon!

Crack Models of Repeating Earthquakes Predict Observed Moment‐Recurrence Scaling

Camilla Cattania, & Paul Segall

Published January 30, 2019, SCEC Contribution #8999

Small repeating earthquakes are thought to represent rupture of isolated asperities loaded by surrounding creep. The observed scaling between recurrence interval and seismic moment, Tr ~ M^(1/6), contrasts with expectation assuming constant stress drop and no aseismic slip (Tr ~ M^(1/3)). Here we demonstrate that simple crack models of velocity-weakening asperities in a velocity-strengthening fault predict the M^(1/6) scaling; however, the mechanism depends on asperity radius, R. For small asperities (Ri < R < 2Ri, where Ri is the nucleation radius) numerical simulations with rate-state friction show interseismic creep penetrating inwards from the edge, earthquakes nucleate in the center and rupture 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 being due to the finite nucleation dimension.

For 2Ri < R <~ 6 Ri simulations exhibit simple cycles with ruptures nucleating from the edge. Asperities with R >~ 6Ri exhibit complex cycles of partial and full ruptures. Here Tr is explained by an energy criterion: full rupture requires that the energy release rate everywhere on the asperity at least equals the fracture energy, leading to the scaling Tr ~ M^(1/6). Remarkably, in spite of the variability in behavior with source dimension, the scaling of Tr with stress drop Dtau, nucleation length and creep rate Vpl is the same across all regimes: Tr ~ (Ri^(1/2) Dtau^(5/6) M0^(1/6)/Vpl. This supports the use of repeating earthquakes as creepmeters, and provides a physical interpretation for the scaling observed in nature.

Citation
Cattania, C., & Segall, P. (2019). Crack Models of Repeating Earthquakes Predict Observed Moment‐Recurrence Scaling. Journal of Geophysical Research: Solid Earth, 124(1), 476-503. doi: 10.1029/2018JB016056.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)