Interaction of slip on asperities: Numerical simulation of seismic cycles on a two-dimensional planar fault with nonuniform frictional property

Numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes. A planar square fault in an infinite uniform elastic medium is considered, and the frictional stress on the fault is assumed to obey a rate- and state-dependent friction law. Nonuniformity in a frictional constitutive parameter is introduced on the model fault. On the fault plane, one or two circular patches with velocity-weakening frictional property are surrounded by velocity-strengthening areas. Unstable slip may occur for velocity-weakening friction and aseismic sliding occurs for velocity-strengthening friction. Velocity-weakening patches correspond to asperities because intense seismic slip may occur there. Simulation results indicate that episodic aseismic slip events (slow earthquakes) occur when the velocity-weakening patch size is close to the critical size of earthquake nucleation. Propagation of postseismic sliding on the velocity-strengthening region follows an earthquake at a velocity-weakening patch. When the postseismic sliding reaches another velocity-weakening patch, an earthquake may be triggered at the patch, resulting in a double earthquake. The time delay between two events of the double earthquake increases with the distance between the two velocity-weakening patches or the degree of velocity strengthening in the region between the patches. When the distance between the two velocity-weakening patches is long, an earthquake at one patch does not directly cause an earthquake at the other patch. In these cases, complex earthquake recurrence may appear due to the interaction between ruptures at the two patches, and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity-weakening patch.