Lawrence Berkeley National Laboratory

Abstract Fluid injections into the deep subsurface can, at times, generate earthquakes, but often, they only produce aseismic deformations. Here we analyze the influence of fault hydromechanical properties on the growth of injection‐induced aseismic slip. Using hydromechanical modeling, we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection. We find that the more pronounced the fault permeability enhancement, the stronger is the growth of the aseismic slip zone. The effect of enhanced permeability is more pronounced when the fault is initially close to failure. Our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases, while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value. Thus, fault permeability increases should be considered as complementary mechanism to current models of fluid‐induced aseismic slip. Plain Language Summary Injection of fluid into the deep subsurface can, at times, generate measurable or even destructive earthquakes, but often, they only produce aseismic deformations along faults and fractures. The relationship between injected pressure and these aseismic deformations is a fundamental point in the estimation of how the crust responds to fluid injection and the associated induced seismic hazard. In this paper, we use data‐driven hydromechanical modeling of fluid injection to show how the fault permeability enhancement in addition to the ambient stress and frictional weakening has an important effect on the fluid pressure diffusion, induced stress perturbation, and the growth of aseismic fault slip. Our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases, while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value. Thus, fault permeability increases should be considered as complementary mechanism to current models of fluid‐induced aseismic slip. These results help to further understand the complex behavior of fault slip caused by fluid injection in nature. Key Points Fault permeability enhancement favors the growth of the aseismic slip zone during fluid injection The larger the fault permeability enhancement, the stronger is the growth of aseismic slip The slip front outpaces fluid pressure diffusion in the fault when fault permeability increases with accumulating slip