Micromechanical Insights Into the Cyclic Behavior of Fault‐Valve Systems

Abstract Cyclic fluid pressurization can promote repeated fault reactivation and transient permeability changes, a behavior often discussed within the fault‐valve concept in which faults alternate between acting as hydraulic barriers and conduits. To investigate the micromechanical processes involved during fluid induced reactivations, we simulate cyclic fluid injection into a pre‐sheared granular gouge using a discrete element model. The simulations reproduce key behaviors observed in laboratory and in situ studies and reveal pronounced cycle‐to‐cycle variability in the onset of reactivation and slip magnitude. Some cycles generate large slip episodes, whereas others produce comparatively small slip under similar loading conditions. Micromechanical analysis of force‐chain evolution reveals a strong inverse correlation between slip magnitude and the population of load‐bearing chains, with sparser force‐chain backbones generating larger slip events. Our results highlight the role of micromechanical processes in controlling macroscopic cyclic fault behavior, offering a physically grounded perspective on fault‐valve behavior.