Effects of Periodic Normal Stress Oscillations on Frictional Properties of Simulated Natural Fault Gouges Under In Situ <i>P</i>‐<i>T</i> Conditions

Abstract Induced earthquakes are occasionally associated with stress oscillations resulting from periodic industrial activities. Yet, the effects of stress oscillations on fault friction under realistic subsurface conditions are not fully clear. We conducted normal stress oscillations experiments using simulated fault gouges derived from the major reservoirs and caprocks of the Changning shale gas field under in situ conditions. Our experimental results reveal that most gouges are velocity‐strengthening under quasi‐static loading. Interestingly, after applying normal stress oscillation, they show similar shear stress evolution with different oscillation amplitudes, frequencies and load‐point velocity, suggesting a negligible effect of the rock composition and the applied P ‐ T conditions. We successfully reproduce our experimental results using an extended CNS (Chen‐Niemeijer‐Spiers) model and the model proposed by Linker and Dieterich (1992, https://doi.org/10.1029/92jb00017 ). Therefore, these experimental observations and friction models can be reliably extrapolated to more heterogeneous field cases and other regions with similar lithology distribution.