Potential Energy as Metric for Understanding Stick–Slip Dynamics in Sheared Granular Fault Gouge: A Coupled CFD–DEM Study

We study the stick–slip behavior in a sheared granular fault gouge using a coupled discrete element method and computational fluid dynamics. We compare characteristics of slip events in dry and fluid-saturated granular fault gouge in drained conditions. The granular layer is confined under constant normal load and sheared with a velocity-controlled mechanism. Potential energy is stored through overlaps between particles. We show that the potential energy builds up during the stick phase and drops during slip instability. Our observations show that on average 8% of the drop in potential energy is converted into particle kinetic energy, while the rest dissipates. Our simulations show that drop in potential energy is a good measure of slip size showing a strong correlation with the drop in macroscopic friction coefficient. Our simulations show that in fluid-saturated granular fault gouge, the potential energy drop is higher leading to a higher drop in friction coefficient and in a higher kinetic energy of particles during slip event.