Friction in faulted rock at high temperature and pressure

Abstract

Two hundred observations of frictional behavior of seven low-porosity silicate rocks were made at temperatures to 700°C and pressures from 2.5 to 6 kbar. For all rocks except one, peridotite, stick-slip occurred at low temperature and gave way to stable sliding at some high temperature, different for each rock. These differences could be related to the presence or absence of minerals such as amphibole, mica, or serpentine. Up to some temperature, depending on rock type, the friction stress was relatively unaffected by temperature. The shear stress decreased at higher temperature, and in some cases such decrease was related to the coincidence of fracture and friction strength. While somewhat dependent on rock type, the friction stress for the seven rocks studied was about the same, within 10–15%. Up to 265°C, water had little effect on the frictional behavior of faulted granite at 3 kbar effective pressure. The frictional stresses measured in the laboratory were significantly higher than estimated for natural faults. This difference could be accounted for by high pore pressure or weak alteration materials in the natural fault zone.