Abstract
Seismic CT was employed to observe how dilatancy of rock localizes before faulting. The seismic CT can map the spatial distribution of P wave velocities. Since P wave velocity is determined by the extent of dilatancy (density, orientation, and aspect ratio of microcracks), mapping the seismic pofile is useful for observing nondestructively the progressive development of dilatancy. The specimen of Ohshima granite was compressed at a constant deformation rate under uniaxial stress. The reconstructions were made within the plane perpendicular to the loading axis. The maps clearly show the metamorphic changes of dilatancy before faulting; at first the formation of diffuse dilatancy occurred, the localization of dilatancy to a few near-surface areas followed at the next stage, and finally a failure zone appeared intersections of localized dilatant areas.
