Nucleation and arrest of aseismic fault slip, during and after fluid pressurization

Fluid pressurization of preexisting faults due to subsurface energy and storage applications can lead to the onset of aseismic slip and microseismicity, and possibly to major induced seismic events.

Fluid injection decreases the fault shear strength and slip occurs when the in situ shear stress on the fault exceeds its shear strength. The nature of slip (aseismic or seismic) depends on the rate at which it occurs and thus on the stability of the deformation. Understanding the mechanics controlling the onset and arrest of aseismic slip and the transition to seismic slip is therefore key to design mitigation strategies for the safe utilization of the subsurface.

In this contribution, we investigate using theoretical and numerical techniques how aseismic slip on a fault plane nucleates, evolves and stops in response to fluid pressurization and its relaxation. We analyze the impacts of the stress regime and the duration of the pressurization event on the aseismic slip propagation and the time to arrest of fault slip after stopping injection. We demonstrate conditions under which there is spatio-temporal self-similarity of (i) aseismic slip profiles during pressurization and (ii) aseismic slip rate profiles after pressurization. We show that post-injection progression and arrest of slip are proportional to the duration of injection. The results presented here provide insights into the mechanics controlling the arrest of aseismic slip after fluid pressurization as a first milestone towards induced seismicity mitigation strategies.