Post-injection aseismic slip as a mechanism for the delayed triggering of seismicity

TL;DR

This study models how aseismic slip continues and propagates after fluid injection stops, potentially triggering delayed earthquakes, with implications for geo-energy operations and seismic hazard assessment.

Contribution

It provides a hydro-mechanical model explaining post-injection aseismic slip propagation and arrest, highlighting its role in delayed seismicity.

Findings

Aseismic slip propagates in pulse-like modes after injection stops.

Faults can host slip pulses much larger than the injection duration.

Post-injection slip may trigger delayed seismic events.

Abstract

Injection-induced aseismic slip plays an important role in a broad range of human-made and natural systems, from the exploitation of geo-resources to the understanding of earthquakes. Recent studies have shed light on how aseismic slip propagates in response to continuous fluid injections. Yet much less is known about the response of faults after the injection of fluids has stopped. In this work, we investigate via an hydro-mechanical model the propagation and ultimate arrest of aseismic slip during the so-called post-injection stage. We show that after shut-in, fault slip propagates in pulse-like mode. The conditions that control the propagation as a pulse and notably when and where the ruptures arrest are fully established. In particular, critically-stressed faults can host rupture pulses that propagate for several orders of magnitude the injection duration and reach up to nearly double the size of the ruptures at the moment of shut-in. We consequently argue that the persistent stressing of increasingly larger rock volumes caused by post-injection aseismic slip is a plausible mechanism for the triggering of post-injection seismicity -- a critical issue in the geo-energy industry. We discuss evidence that supports this mechanism based on documented cases of post-injection-induced seismicity.