Fluid conducting fault zone and their long-term behavior in crystalline rocks -An example from orogenic field of Japan-

Fault zone distributed in crystalline rock inevitably influence fluid transport and solute migration. Most evaluations of those fluid conducting features and contaminant migration processes have been conducted mainly by the present hydrological characteristic for deep underground usages (e.g. for high level radioactive waste (HLW) disposal and LPG storage). Relatively little attention has been given to the possible long-term behavior and evolution of these features, and their influence on fluid flow and geochemical interaction after the installation of engineered materials underground. In the orogenic field of Japan, there are wide areas of crystalline rocks. The rocks in each area have a distinctive history that is partly reflected in the characteristics of the displacement system including fault zone and fractures, and associated mineral fillings that occur. These characteristics generally imply that fluids can flow through those networks developed in and around fault zones or crushed zones. The structural and mineralogical features readily illustrate how fluid interacts by the fillings and open pore geometry, due to the dissolution and precipitation. The work presented here seeks to provide geological evidence that natural long-term physical and chemical processes are unlikely to change the overall transport properties of the rock significantly. Here, as present understandings provided from URL, LPG storage site and Atera active fault study, describes fault zone and related fracture systems that are developed in intrusive crystalline rocks within the Japanese orogenic belt, and the fluid transport properties of the fluid systems. Mineralogical studies and dating analyses of fracture fillings also suggest that structurally the features are relatively stable after the present hydrogeological setting established. The studies on fluid conducting geometry show the unique characteristics of those forming process and the geometries in crystalline rocks distributed within the orogenic belt. This geological evidence also enables us to provide a model to build confidence in a technical approach applicable for hydrogeological and geological modeling over long time scales under the orogenic stress field present in Japan. The model can be transferred for other host rocks, as well as for characterizing a site in crystalline rocks at a continental margin in order to allow the underground environment to be exploited.