The influence of cementation on fault stability

Fault healing is a crucial part of the seismic cycle, allowing faults to lock and restrengthen during the interseismic period in preparation for a future earthquake. Laboratory studies show that fault healing occurs through time- dependent growth of asperity contact area, via plastic flow, and diffusional mechanisms that increase contact strength at constant area. However, natural seismic cycles have significantly longer interseismic periods than are studied in the lab, and thus additional mechanisms such as cementation and mineral growth may play a role. In fact, the role of cementation, defined as the precipitation of mechanically strong minerals, in influencing fault stability remains largely underexplored. Here, we present laboratory work integrated with mineral and microstructural studies investigating how cementation and frictional healing influence fault slip behavior. Cementation results in much larger fault restrengthening than frictional healing and this promotes unstable slip. Our results show that cementation induces a time-dependent increase of fault cohesive strength and that this scales with stress drop of lab earthquakes. We suggest that cementation is a fundamental mechanism that influences the seismic potential for natural and fluid-injection induced seismicity.