Spatial distribution and characteristics of fracture zones near a long-lived active fault; A Field-based study for understanding changes in underground environment caused by long-term fault activities

Niwa, Masakazu   ; Kurosawa, Hideki; Ishimaru, Tsuneari 

Fracture zone development has a substantial impact on long-term changes in the underground environment because fracture zones are leading candidates as groundwater flowpaths as well as a locus for mechanical disturbance by fracturing. For understanding fracture zone development we surveyed the spatial distribution and characteristics of fracture zones in an area 4 km to the north and 6 km to the south from the western part of the Atotsugawa Fault, a long-lived active fault in central Japan. This study suggests that fracture zones along the Atotsugawa Fault act as a major conduit controlling regional groundwater flow. Based on rock features and deformation fabrics at meso- and microscopic scales, once fracture zones had formed, epigenetic deformation was concentrated in the ancient fracture zones.