Reconstructing the evolution of fault zone architecture; Field-based study of the core region of the Atera Fault, Central Japan

Niwa, Masakazu   ; Mizuochi, Yukihiro*; Tanase, Atsushi*

Architecture of fault/crush zones and their development histories are closely linked to the long-term stability of the underground environment. Herein, we studied part of the Atera Fault System, one of several large, active faults in Central Japan, and described the detailed mesoscopic and microscopic features of a crush zone to reveal its development at higher structural levels of the fault (i.e. several hundred meters to kilometers in depth). The zone is characterized by brittle fracturing and rock mass pulverization, lacks both ultracataclasite bands and any deformation structures showing pressure solution. The characteristics of the deformation structures suggest that the exposed crush zone was formed at a depth of less than several kilometers. Features of clay mineral and carbonate precipitations in the zone indicate the repetition of intense fragmentation and shear localization through periodic activities on the Atera Fault after the Pleistocene.