A study on the viscous characteristics of granular fault gouge under low and high slip rates

The viscous characteristics of granular fault gouge significantly impact the dynamic mechanical behavior of faults, yet the problem of determining the viscosity of these interlayers at different slip velocities remains unresolved. This article presents theoretical research on this issue. The Maxwell relaxation model was employed to study the evolution of force chains in granular fault gouge during slow shearing of granular gouge, and the dependence of force chain length on shear strain rate, effective extension speed of shear bands, and strength of the granular medium was derived. The relaxation time of the shear band in granular fault gouge, the expression for the viscosity coefficient of the granular medium, and the conditions for the transformation of solid-liquid mechanical behavior of the granular medium were established. The validity of this model was verified through comparison with existing experimental data. For high-speed fault slip shear, the motion of the granular medium exhibits turbulent characteristics. Statistical physics was used to describe the interaction between granular particles in granular fault gouge, and it was found that the viscosity coefficient is inversely proportional to the shear rate at high slip rates. The research results have fundamental significance for understanding the viscous and other physico-mechanical properties of granular gouge in faults.