Scaling of seismic and aseismic moments of natural and induced earthquakes

A growing body of in-situ experimental data suggests that stimulating faults through the injection of pressurized fluids can trigger both aseismic and seismic slip. The simultaneous occurrence of aseismic and seismic slip can be explained by a fault pressurization mechanism that facilitates the nucleation of aseismic ruptures. Stress concentration at the leading edges of these advancing aseismic cracks triggers seismic slip on brittle asperities. This mechanism has also been proposed to explain the behavior of shallow (<10 km) faults during well-documented slow slip events (SSEs). Observations of these SSEs, particularly in extensional and transform settings, reveal a power-law scaling relationship between seismic and aseismic moments across several orders of magnitude.

We have extended the scaling of crustal SSEs to encompass induced seismicity, in-situ experiments, and laboratory earthquakes. Our findings show that power-law scaling remarkably applies to lower magnitude slow slip transients, including those observed up at the laboratory scale. However, there is an observational gap for SSEs with magnitudes between Mw 0-4. To address this gap, we employed numerical simulations of SSEs and their associated seismicity, integrating a poroelastic model with a stochastic earthquake simulator. The simulated distributions of aseismic and seismic moments align well with the natural and induced cases, maintaining the established scaling. Our results support the hypothesis that stress changes resulting from aseismic slip are the primary driving mechanism, while fluid-fault pressurization is crucial for the nucleation of aseismic slip. Furthermore, varying levels of confining stress help explain the depth-dependent variability in the ratio between aseismic and seismic slip. Overall, our findings suggest that the process governing the transition from aseismic to seismic release due to fluid pressurization are consistent across both nature to laboratory scales.