Scaling of small repeating earthquakes explained byinteraction of seismic and aseismic slip in a rate andstate fault model

摘要

Because of short recurrence times and known locations, small repeating earthquakespresent a rare predictable opportunity for detailed field observations. They are used tostudy fault creeping velocities, earthquake nucleation, stress drops, and other aspects oftectonophysics, earthquake mechanics, and seismology. An intriguing observation aboutrepeating earthquakes is their scaling of recurrence time with seismic moment, which is significantly different from the scaling based on a simple conceptual model of circularruptures with stress drop independent of seismic moment and no aseismic slip. Herewe show that a model of repeating earthquakes based on laboratory-derived rate and statefriction laws reproduces the observed scaling. In the model, a small fault patchgoverned by steady state velocity-weakening friction is surrounded by a much largervelocity-strengthening region. Long-term slip behavior of the fault is simulated using amethodology that fully accounts for both aseismic slip and inertial effects of occasionalseismic events. The model results in repeating earthquakes with typical stress dropsand sizes comparable with observations. For a fixed set of friction parameters, theobserved scaling is reproduced by varying the size of the velocity-weakening patch., Insimulations, a significant part of slip on the velocity-weakening patches is accumulatedaseismically, even though the patches also produce seismic events. The proposed modelsupplies a laboratory-based framework for interpreting the wealth of observations aboutrepeating earthquakes, provides indirect evidence that rate and state friction acts on naturalfaults, and has important implications for possible scenarios of slip partition into seismicand aseismic parts.