A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault

► Samples from the San Andreas Fault Observatory at Depth (SAFOD) were studied. ► Foliated rocks in the fault core were developed by alternating pressure solution and cataclasis. ► The active creep mechanism is a granular-type flow that involves both frictional sliding and pressure solution. ► The microseismicity involves local fluid pressure build-up in regions of fracture-and-seal and material contrast.