Complexity in earthquake sequences controlled by multiscale heterogeneity in fault fracture energy

A series of dynamic rupture events under constant tectonic loading is simulated on a fault with multiscale heterogeneity and a stochastic rupture initiation process. The fracture energy of the fault plane is assumed to have multiscale heterogeneous distribution using fractal circular patches. The stochastic rupture initiation process as a function of the accumulated stress is introduced in order to take account of unknown smaller-scale heterogeneity and variability. Five realizations of a statistical spatial distribution of fracture energy (fault heterogeneity maps) are tested for the simulations of earthquake sequences during a few seismic cycles. The diversity of earthquake sequences is principally controlled by the spatial distribution of the patches. The effect of dynamic rupture appears in the residual stress after the characteristic events because of their directivity and this localizes the subsequent sequences. Although the characteristic earthquakes occur rather regularly in time and similarly in different seismic cycles, some irregular behavior is found based on the heterogeneity maps and the randomness of the preceding earthquake sequence, leading to a visible anomaly in the seismicity. Such anomalies are not predicable but understandable through the analysis of the considered earthquakes during the cycle. The similarity and the diversity simulated in this study, governed by the structure of an inherent distribution of multiscale heterogeneity, suggest the importance of the pre-existing heterogeneity field along the fault for the appearance of earthquake sequences, including those that are characteristic.