The effect of water on strain localization in calcite fault gouge sheared at seismic slip rates

Strain localization during coseismic slip in fault gouges is a critical mechanical process that has implications for understanding frictional heating, the earthquake energy budget and the evolution of fault rock microstructure. To assess the nature of strain localization during shearing of calcite fault gouges, high-velocity (vmax ¼ 1 m=s) rotary-shear experiments at normal stresses of 3e20 MPa were conducted under room-dry and wet conditions on synthetic calcite gouges containing dolomite gouge strain markers. When sheared at 1 m/s, the room-dry gouges showed a prolonged strengthening phase prior to dynamic weakening, whereas the wet gouges weakened nearly instantaneously. Microstructural analysis revealed that a thin (