Elastic interaction of parallel rate-and-state-dependent frictional faults with aging and slip laws: slow-slip faults can sometimes host fast events

In contrast to surface observation of complex earthquake faults, simple fault-plane models are frequently sufficient to fit geophysical data of seismic wave or crustal deformation. However, earthquake occurrence should be strongly affected by fault interaction between separate faults. To understand its mechanics, rate-and-state frictional models of separate faults within elastic continuum would be important. We construct a conceptual out-of-plane model of aligned parallel faults (causing stress shadows) in a two-dimensional elastic body, assuming both "aging" and "slip" type of state evolution laws. We find that close fault conditions (roughly for smaller inter-fault distance than fault length) favor higher-speed slip events than distant fault conditions. In a practical sense, the elastic interaction only affects faults that are hosting slow events. This point does not depend on the state evolution laws (aging or slip). Our result implies that the parallel distribution of the frictional faults contributes occurrence of relatively fast slip in a slow-slip region.