The Dependence of Constitutive Properties on Temperature and Effective Normal Stress in Seismogenic Environments

We have evaluated how the parameters prescribing the slip-dependent constitutive law are affected by temperature and effective normal stress, by conducting the triaxial fracture experiments on Tsukuba-granite samples in seismogenic environments, which correspond to a depth range to 15 km. The normalized critical slip displacement Dc almost remains constant below 300oC (insensitive to both temperature and effective normal stress reff n ); Dc increases with increasing temperature above 300 C, and the rate of Dc increase with temperature tends to be largest at higher reff n . The breakdown stress drop Dsb for the granite at constant reff n is roughly 80 MPa below 300 C, and does not depend on reff n . Above 300 C, Dsb decreases gradually with increasing temperature, and the rate of Dsb reduction with temperature increases at higher reff n . The peak shear strength sp increases nearly linearly with increasing reff n below 300 C. However, sp becomes lower above 300 C, deviating from the linear relation extrapolated from below 300 C. This is consistent with the onset of crystal plastic deformation mechanisms of Tsukuba granite.