A review of frictional sliding on brine-penetrated faults in salt

Abstract

We review and discuss experimental observations of the frictional sliding of porous, fluid saturated faults in salt. In previous work, granular salt has been used almost exclusively as an analogue for quartz under hydrothermal conditions due to its high solubility at room temperature. However, the frictional behavior of salt itself is of interest, since localized frictional or frictional-viscous shear might occur at low effective stresses, such as those expected if migrating brine permeates localized zones during salt tectonics or after cavern abandonment. Results from slide-hold-slide experiments, performed at room temperature and an effective normal stress of 1, 2.5 and 5 MPa, show that porous/granular faults in salt regain strength within hours. Slip-dependent weakening, velocity-weakening and stick-slip behavior were observed during sliding at constant velocity, implying significant potential for unstable, localized deformation under fluid-saturated conditions. The results demonstrate that localized frictional or frictional-viscous shear of salt could occur in fluidpermeated zones at interfaces between lithologies, is potentially unstable and might provide pathways for fluid expulsion.