The Seismic Cycle on Rate and State Faults with Different Evolution Laws and Fault Geometries

Earthquakes occur by sudden slippage along pre-existing faults via a frictional instability. Laboratory-derived rate and state friction laws have emerged as powerful tools for investigating the mechanics of earthquakes. Two types of state‐variable evolution laws are commonly used to fit the experimental data, the aging and slip laws. The aging evolution law has been used extensively to model the earthquake cycle, including the nucleation, dynamic rupture propagation and arrest, and interseismic period. The slip law, which generally provides a better fit to rock friction experiments, has rarely been used in simulations of the whole seismic cycle. In addition, faults are zones with complex internal structure and non-planar geometry, which also affect the rupture process during the seismic cycle.

In this study, I examine the effects of fault geometry, state evolution law, and friction parameters on the earthquake source process with fully dynamic 2-D simulations of earthquake sequences on planar and non-planar faults. The numerical approach accounts for all stages in the seismic cycle and enables modeling slip that is comparable to the minimum wavelength of roughness. I test the statistics of the events in terms of static source parameters and analyze in detail the rupture process during the nucleation and dynamic propagation stages. For the same friction parameters and fault geometry, the slip law results in a more rapid weakening of the friction coefficient than the aging law. That leads to ruptures with smaller nucleation sizes, larger slip rates, and larger rupture speeds for the slip law, including transition to supershear. With the aging law, a small level of fault roughness is enough to introduce considerable complexity into the rupture process, with larger amount of aseismic slip and larger variability in earthquake sizes.  For the same level of roughness, those effects are significantly smaller in the case of the slip law.