Omid Dorostkar, Jan Carmeliet

Mature faults with rough surface at their core contain granular gouge, however, the presence of fault gouge is mostly disregarded in the analysis of effect of fault’s surface roughness on the mechanics and stability of faults. In this work, we consider a rough fault system with constant roughness at the wall-gouge interaction and study the effect of grain friction on the characteristics of seismic cycles. Our discrete element simulations show that the stick-slip frictional strength and dilation of the rough fault system, as well as their variations, nonlinearly increase with the particle friction, but at high particle friction saturate. By statistical analyses on a large number of slip events, we find that the average recurrence time and its variations decrease with particle friction. A rough fault with higher grain friction shows more small slip events, but also contains a limited number of extreme events and demonstrates a more complex nucleation phase with higher stored energy. We analyze the pseudo acoustic emission, which is based on monitoring of the velocity signal of particles, and find higher temporal and more spatially distributed acoustic emissions for rough fault with higher grain friction. Our findings in this study show that, in rough faults with granular gouge, where the fault zone walls are totally engaged to the granular gouge, the friction at grain scale controls the characteristics of stick-slip cycles showing similar influence on the mechanics of faults as the roughness of fault’s surface in absence of fault gouge.