Earthquake Cycles and Seismic Source Processes on Carbonate Faults: Insights From Microphysically-Based Modeling

The source process of natural earthquakes, involving spontaneous fault slip and complex deformation processes within the fault zone, remains poorly understood. Despite advances in understanding earthquake nucleation and rupture propagation, a model capturing the full range of velocities and associated deformation mechanisms is still lacking. Existing studies often fail to integrate the contributing mechanisms comprehensively, limiting simulation of earthquake behavior at varying depths and loading velocities. This study addresses this gap by extending a microphysical friction model, originally developed for earthquake nucleation, to simulate the entire seismic cycle on a carbonate fault, using a spring-slider analog. The model predicts steady-state friction as a function of velocity (v) and depth, revealing a transition from v-strengthening to -weakening with increasing depth or decreasing velocity, and dynamic weakening at seismic velocities at all depths. These predictions align with previous laboratory results. Depths simulated range from the surface to the nucleation zone. At shallow depths featuring v-strengthening friction (<4 km), the model predicts a range of slip behaviors at a rupture front, from catastrophic events to small slow-slip events with significant afterslip, depending on whether the peak resistance inherent in the model is surpassed during acceleration. At depths featuring nucleation (≥4 km), the model predicts spontaneous earthquake cycles with well-defined source characteristics. Notably, the predicted slip pulses resemble the classic or regularized Yoffe function, suggesting a self-healing rupture mode. The extended model improves our understanding of earthquake source processes and provides a potentially powerful framework for simulating earthquake behaviors on carbonate faults.