Evolution of Principal Slip Zone in Sheared Granular Fault

Abstract The natural faults show a spectrum of slip modes due to different geological conditions. How the principal slip zones (PSZs) evolve in these faults remains a puzzle. Here, a series of numerically simulated sheared granular faults that incorporate breakable grains under different loading conditions (normal stress, shear velocity, and load stiffness) are adopted to explore the detailed evolution of PSZs. With the increased normal stress, the faults show more distinct stick-slip cycles, and the slip modes gradually switch from stable sliding to stick-slip. The faults produce larger slip events when the shear velocity increases to the scale of slip velocity of the slip events, and higher load stiffness tends to yield stable sliding states. Additionally, when subjected to higher normal stresses, tenser shear localization in the granular gouge can be observed, and PSZs prefer to initiate from places further away from the plates and can expand more widely before entering a stable state. Also, when subjected to higher normal stress or lower shear velocity, the PSZs expand faster. However, the load stiffness has a minor influence on the development of PSZs. This paper illustrates the progression of PSZs under various loading conditions, providing a more comprehensive understanding of the formation and evolution mechanism of PSZs in sheared granular gouges.