Statistical modeling of 3D seismicity and its correlation with fault slips along major faults in California

Abstract

This study applies a 3D Epidemic Type Aftershock Sequence (ETAS) model to the earthquake catalog in California. A new depth kernel function incorporating the scaling effect of mainshock magnitudes is introduced into the model. The results demonstrate that the new model improves data fitting, and we find a consistent decrease in aftershock productivity with depth by stochastic reconstruction. We attribute this to the decreasing fault coupling with depth or active seismic faulting in the upper crust. Furthermore, we compare background seismicity rates derived from the new model with the long-term slip rates on the faults in the study region. We reveal a linear increase in the seismicity rate with the slip rate on the logarithmic scale, suggesting the accumulated strain on fault is partially released by seismic activities. Additionally, a significant correlation exists between the background seismicity rate and fault segments exhibiting relatively high creep rates, especially in the transition zones for fault coupling along the central San Andreas fault. This finding suggests that interseismic background earthquakes mostly occur in areas with moderate coupling ratios.