Mechanical properties of ultrafine quartz, chlorite and bentonite in environments appropriate to upper-crustal earthquakes

Abstract

This dissertation is concerned with understanding frictional deformation mechanisms in the context of earthquake prediction. Using experimental rock deformation techniques, attempts are made to simulate realistic hypocentral environments for upper-crustal earthquakes, with the purpose of elucidating characteristics of the operative deformation mechanisms important in determining constitutive equations for frictional processes and instabilities. In particular, the effects of temperature and pore water pressure are investigated in friction experiments simulating the environment expected along a fault between 5 and 10 km depth. Using a triaxial apparatus, thin layers (<1 mm) of powders of quartz, chlorite and bentonite are sheared in a 35(DEGREES)-sawcut configuration in Tennessee sandstone, dry at 150 MPa confining pressure, or wet at 250 MPa with a pore water pressure of 100 MPa. Specimens are deformed at a shear strain rate of approximately 10('-2) or 10('-3) s('-1). The effect of temperature to 300(DEGREES)C in the mineral powders tested generally is to increase frictional resistance slightly and to promote, rather than to suppress, unstable frictional response. For ultrafine quartz, frictional strength at 600(DEGREES)C is the same as at room temperature. However, microscopic evidence for porosity reduction with increasing temperature marks progressive changes in contact area between grains. These effects are wholly consistent with previous reports of the effects of strain rate on frictional response, and lead to the conclusion that underlying creep processes at discrete contacts between frictional surfaces are fundamental to the explanation of a variety of frictional phenomena, including stick-slip. ...