The role of frictional heterogeneities, stress-state and fluid flow on fault slip behavior during fluid pressure perturbations.

In the last 15 years, activities for geo-energy production are associated to subsurface fluid injection in enhanced geothermal systems,  for enhanced oil recovery, for the disposal of wastewater or for carbon dioxide capture and storage. In several regions, M>3 earthquakes occurred following fluid injection, and some of these earthquakes have caused extensive damage, putting geo-energy production projects at risk of being discontinued. Evaluating the conditions under which fluid injection can induce earthquakes is therefore important to safeguard local infrastructures and to ensure continuity of geo-energy projects.  

To shed light on the effect of fluid injection on a fault located in the proximity of a reservoir, we implemented into the Q-DYN seismic cycle simulator the fluid diffusion equation (one-way coupling). We ran models of seismic cycles on a rate-and-state-dependent fault under a quasi-dynamic approximation, and we developed a systematic study to assess how fault frictional heterogeneities, the stress state of the fault upon injection, the timing of injection relative to the phase of the seismic cycle and factors controlling fluid flow, i.e. permeability, porosity, flow-rate, influence fault slip behavior and earthquake magnitude. 

Our results show that localized pore-pressure perturbations allow us to gain deeper physical insight into the propagation and arrest of earthquake ruptures and that changes in the fault physical properties can promote a spectrum of fault slip behavior and recorded magnitudes.