Fault rock heterogeneity can produce fault weakness and reduce fault stability

Geological heterogeneity is abundant in crustal fault zones; however, its role in controlling the mechanical behaviour of faults is poorly constrained. This study presents laboratory friction experiments on laterally heterogeneous faults with patches of strong, rate-weakening quartz gouge and weak, rate-strengthening clay gouge. The experiments show that heterogeneity leads to a significant reduction in strength and frictional stability compared to compositionally identical faults with homogeneously mixed gouges. Weakening effects include smearing of weak clay, differential compaction redistributing normal stress, and shear localization producing stress concentrations in strong quartz patches. The results demonstrate that geological heterogeneity significantly impacts fault strength and stability, influencing slow-slip transients versus earthquake ruptures. Further research in lab experiments and earthquake source modeling is needed.

John D. Bedford, Daniel R. Faulkner, Nadia Lapusta