Fault slip behaviors and frictional stability controlled by particle size of fault gouge under fluid injection

Understanding the control mechanism of fault rock particle size in fluid-induced fault slip and rupture processes is crucial for mitigating the seismic risks associated with large-scale fluid injection. Here, we conducted laboratory experiments to present the effects of fault rock particle size on slip behavior, friction, and slip modes under fluid injection. Our results demonstrate that the particle size of the gouge controls the initiation of fault slip events and that the fluid pressure required for the initial fault slip is negatively correlated with the rock particle size. The increase in rock particle size can weaken the faults and induce the transition of the fault slip mode from creep to slow stick-slip events, which leads to the occurrence of seismic events. These results reveal the particle size of fault gouge exerts a potentially dominant control on the slip behavior, slip modes, and frictional characteristics of faults under fluid injection, providing crucial insights into fault slip and seismic events.