The influence of cementation on faults frictional stability

Fault healing is a crucial mechanism for the seismic cycle allowing faults to lock and restrengthen during the interseismic time. Several studies also suggested that the rate of fault healing controls the magnitude and recurrence time of earthquakes both in laboratory and nature. Experimental works show that fault healing, at the laboratory time-scale of 1 to 10⁵ s, is dominantly a frictionally-driven process which derives from the time-dependent growth of the contact area due to plastic yielding of asperities. However, seismic cycles in nature are considerably longer and thus other healing mechanisms such as cementation are more effective. Cementation is a chemically-driven process commonly observed in the field where cataclasites characterize the core of several exhumed tectonic faults.  Nevertheless, laboratory studies on the role of cementation on fault stability are still few because the limited time-frame of the laboratory approach which hinders an effective characterization of the process. Here we present a different experimental approach to overcome this limitation. By using an analogue fault gouge made of hydraulic cement in both nominally dry and fluid saturated conditions, we investigate how frictional and chemical (cementation) healing influence fault slip behavior. Microstructural analysis shows the pervasive precipitation of newly-formed minerals in the fluid-saturated gouge, coherently with the expected cementation reaction. In these experiments, cementation results in larger and non-log-linear restrengthening of the experimental fault compared to frictional healing. Our results show that cementation also promotes unstable slip, inducing a time-dependent increase of fault cohesive strength that scales with time as the observed stress drop during instabilities. We thus suggest that cementation is a fundamental mechanism during interseismic time that controls the seismic potential of faults, even at shallow depths, with relevant implications for natural and induced seismicity.