Quantifying the role of aseismic slip in the source processes of induced earthquakes

Understanding the triggering mechanisms of induced earthquakes is the key to effective seismic hazard mitigation. Various mechanisms have been proposed in the past decades, with more recent studies suggesting complex driving forces that involve aseismic motion on the fault. The interplay of seismic and aseismic motion in the context of induced seismicity is particularly intriguing because of the complex interaction among fluid, frictional fault interface and the evolving state of stress during and after the injection.

We aim to characterize, through numerical modeling of rate-and-state faults, the aseismic motion on a fault that is subjected to fluid-induced stress perturbation. We consider its effect on both the timing and size of subsequent induced seismic events. Our fault model features a velocity-weakening (VW) patch embedded in a large velocity-strengthening (VS) region. It is subjected to various levels of shear stress perturbations at different times during a certain seismic cycle, representing the case of far-field injection with no direct hydrological connection, i.e. fluid does not directly reach and impact the fault. We observe a wide range of aseismic responses from the fault that lead to either the advancing or delaying of the next seismic event and the triggering of smaller seismic events that rupture the VW patch partially. One interesting finding is that the delaying of the induced event tends to happen when the level of stress perturbation is low (< 0.1 MPa) and when the perturbation occurs late in the interseismic period (> 85%).

Our ongoing work is directed toward an analogous set of models that assume the presence of fluid on the fault, as represented by the perturbation of normal stress instead. We will also explore additional effects of dynamically evolving friction parameters. The subsequent step is then to incorporate specific fault frictional properties and fluid injection histories to match with field conditions, such as those in the Central United States. We aim to provide observables that can be tested in geophysical observations or drilling experiments, and ultimately to better constrain the range and timing of stress perturbations that are favorable for certain fault responses that induce earthquakes