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Seismicity, Fault Slip Rates, and Fault Interactions in a Fault System

Seismicity and the partitioning of slip rates in interacting and mechanically coupled fault systems are poorly understood. We developed and used three‐dimensional viscoelastoplastic finite element models to simulate earthquakes, earthquake cycles, and synthetic seismicity in single and bifurcated fault systems and investigate seismicity, fault slip rates, and interactions and mechanical coupling between faults in fault systems. The modeled interseismic velocities and coseismic displacements are consistent with those from analytical and quasi‐analytical solutions. We found that the modeled frequency‐magnitude relation satisfies the Gutenberg‐Richter relation and the b value is inversely related to differential stress. We observed that the seismicity on two parallel faults is often interdependent and complementary: high seismic moment release rates on a fault are usually accompanied by low ones on the other fault and vice versa; the two faults collectively accommodate far‐field tectonic loading and crustal relative motion. Model results showed that when two parallel faults have the same or similar strength, they have similar seismicity and long‐term slip rates, but when one of the two faults has lower strength, it has more active seismicity and a faster slip rate than the other; the sum of their slip rates equals the far‐field crustal relative motion in both cases. The results in this study provide scientific insights into the spatiotemporal migration of seismicity and partitioning of fault slip rates in an interacting and mechanically coupled fault system and help to qualify b values and to evaluate the earthquake hazard and risk on each of the faults in such a system.