Effect of mineralogy on friction-dilation relationships for simulated faults: Implications for permeability evolution in caprock faults

This paper experimentally explores the frictional sliding behavior of two simulated gouges: one, a series of quartz–smectite mixtures, and the other, powdered natural rocks, aiming to evaluate and codify the effect of mineralogy on gouge dilation and frictional strength, stability, and healing. Specifically, velocity-stepping and slide-hold-slide experiments were performed in a double direct shear configuration to analyze frictional constitutive parameters at room temperature, under normal stresses of 10, 20, and 40 MPa. Gouge dilation was measured based on the applied step-wise changes in shear velocity. The frictional response of the quartz–smectite mixtures and powdered natural rocks are affected by their phyllosilicate content. Frictional strength and healing rates decrease with increasing phyllosilicate content, and at 20 wt.% a transition from velocity-weakening to velocity-strengthening behavior was noted. For both suites of gouges, dilation is positively correlated with frictional strength and healing rates, and negatively correlated with frictional stability. Changes in the permeability of gouge-filled faults were estimated from changes in mean porosity, indexed through measured magnitudes of gouge dilation. This combined analysis implies that the reactivation of caprock faults filled with phyllosilicaterich gouges may have a strong influence on permeability evolution in caprock faults.