Transition between frictional slip and ductile flow for halite shear zones at room temperature.

A complete transition from frictional slip to ductile shearing flow upon decreasing velocity (or slip rate) or increasing confining pressure is documented for a thin layer of halite undergoing large shearing deformation. The results indicate that the logarithmic law for steady-state friction with a negative velocity dependence breaks down when friction becomes nearly equal to the shear resistance required for ductile flow and that the law changes into a flow law in shear upon further decrease in velocity. The frictionvelocity relation is crucial in stability analyses of fault motion, and the results are important for earthquake and state-of-stress problems, especially in the application of laboratory data to the slow average motion of natural faults and to the behavior of deep faults along which ductile deformation becomes increasingly predominant.