Difference of microscopic texture between fault gouges and hydrothermal clay veins

Niwa, Masakazu   ; Shimada, Koji   ; Aoki, Kazuhiro ; Seshimo, Kazuyoshi ; Tanaka, Yoshihiro; Okubo, Nariaki   ; Kondo, Keietsu  ; Yasue, Kenichi; Ishimaru, Tsuneari ; Umeda, Koji

Hydrothermal clay veins in granite show similar appearance to clay-rich fault gouge in field outcrops. Thus precise identification of earthquake-related fault gouge, including discrimination from aseismic clay veins, is important for a reliable seismic hazard assessment. In this study, in-depth description was carried out for samples of a fault gouge and a clay vein from the Kojaku Granite in the western part of the Tsuruga Peninsula, central Japan. Observation of the clay-rich gouge and vein using scanning electron microscope and transmission electron microscope revealed clear difference of their microscopic textures, regardless of their clay mineral compositions.