Complexity in the Earthquake Cycle Increases with the Number of Interacting Patches

Numerical simulations were performed to examine the effects of heterogeneity of frictional properties on earthquake cycles. In the model, rate- and state-dependent friction was assumed at a planar fault in an infinite uniform elastic medium. Simulated earthquake cycles were compared at model faults with one to four circular patches with velocity-weakening frictional properties. The characteristic slip distances for the patches were varied so that the effects of interactions between patches with different frictional properties could be assessed. Simple periodic, multiperiodic, and aperiodic earthquake cycles were observed in the simulation results. The frequencies of the multiperiodic and aperiodic cycles increased with the number of velocity-weakening patches, suggesting that more complex cycles may occur in a fault as the frictional properties become more heterogeneous. The simulated earthquake cycles were divided into several classes according to the combinations of ruptured patches in the earthquakes. Complex aperiodic earthquake cycles tended to occur when the values of the parameters lay between the parameter ranges for the different patterns. The frequency distribution of simulated earthquake recurrence intervals became more continuous and smooth as the number of patches increased. The simulation results suggest that interactions between many patches with different frictional properties form part of the explanation of realistic complex earthquake cycles.