抄録
Fracture nucleation in which instability occurs may be produced before earthquakes on the recent papers for fracture mechanics. The formation process of the fracture nucleation have been studied by the various models on physical and chemical bases, that is, slip weakening on a pre-existing fault, stress corrosion cracking and localization of microcracks. This paper suggests that a fracture nucleated region will be generated because of localization of microcracks as the differential stress in the crust is increased, in which ultimately dynamic rupture can be led due to sudden coalescence of cracks. We examined the precursor changes such as elastic wave velocities, attenuation, wave form, stress and strain in a seismic source region before earthquakes, on the basis of the fracture nucleation process which we have been investigated using an elastic wave tomograpy technique during triaxial compression tests. We also estimated the strength about 12km deep in the crust in order to evaluate a potential whether the fracture nucleation can be produced actually or not, considering the existence of water and pre-existing faults in the crust.
