Understanding the role of rock heterogeneity in controlling fault strength and stability

The rock heterogeneity exists widely in fault zones; however, the intrinsic mechanism of how it affects the mechanical behavior of faults is poorly understood. To develop a quantitative understanding of the effect of the rock heterogeneity on the strength and stability of faults, here we investigate a pore-pressure model based on rate- and-state friction in the manner of two-degree-of-freedom spring-sliders and analyze the reasons of fault weakening and the conditions of frictional instability by carrying out nonlinear simulations and a linear stability analysis. We find that the strength of heterogeneous faults depends largely on the compaction difference (or differential compaction) between the two gouges (e.g. quartz and clay), and the stability is affected by the proportion of the two gouges patches. Our model implies that the rock heterogeneity is likely to weaken faults and reduce the stability of faults.