ON THE CONSTITUTIVE CRITERIA FOR THE FAULT: INFLUENCEOF SIZE AND TENSILE CRACKS GENERATION DURING RUPTURE

摘要

In recent studies the authors consider the possibility of occurrence of tensile crack generation near thefree surface during faulting. The main assumption is that the dynamic tensile stress created during the shearrupture process would be dominant over the background stress near the free-surface. The proposed model wasable to simulate the mechanism of cracks developed as a flower like-structure surrounding the shear fault in thevicinity of the free surface and explain some aspects of the fracture zones found after the 2000 Tottoriearthquake.The applicability of various constitutive laws for the fault employed in numerical analysis of the nearsource motion, such as the slip-weakening, velocity-weakening or rate- and state-dependent friction laws, werealso recently discussed by the authors in connection with results of laboratory experiments on friction.In this paper, the most important conclusions of the studies outlined above are summarized by way ofintroduction to the numerical modeling of the region adjacent to the fault surface, which includes material nonhomogeneitiesas well as the possibility of generation of new tensile cracks. In the presence of fracture, bothfactors exert important influence on the macro constitutive laws for the fault, which relate the static (meannormal and shear stresses) with kinetic (displacements) variables, as well as with their time derivatives. Bymeans of simulation, it is shown that the coefficients in the equation that relate the relevant variables depend onsize, that is, they vary with the contact area over which stresses, displacements and velocities are averaged. Anyvariability in Young's modulus or mass density of the surround rock may however be neglected, the onlysignificant random fields being those that describe friction at the interface and the specific fracture energy.