How Far does the Influence of Faulting Extend

Abstract

Faults are always accompanied by fracture zones, regardless of their dimensions. The characteristics and distribution of fault fracture zones in basement rocks have been extensively clarified, because their existence is taken into account in the site selection and safety design of large structures, such as large dams, underground power stations and nuclear power stations. Recently, materials that constitute fault fracture zones have been investigated and classified as “fault rocks, ” a new category. In field investigations, simple description of “fracture zone” is insufficient. As observations at fault outcrops and optical microscopy can easily distinguish fault rocks, types of fault rocks should be described in detail. Zones influenced by faulting have been found around faults. These zones are called process zones. A process zone is characterized by a greater number of joints, secondary shear fractures and microcracks. It is difficult to know whether or not faulting directly produces all these structures. The existence of a process zone probably influences on the long-term circulation of underground water and diffusion of materials. Characteristics of the process zones should be clarified, in order to facilitate the safe depository of high-level nuclear wastes into geological formations.