Deformation history of the Atera fault, central Japan

Zwingmann, H.*; Niwa, Masakazu   ; Todd, A.*

Active inland faults are widespread in Japan and investigations are important for earthquake forecasting and seismic hazard assessments. We describe authigenic illite fault gouge age dating results from a unique outcrop of the active Atera Fault, central Japan. This study investigates the timing of fault formation by K-Ar dating of authigenic illite separated from 3 fresh, non-weathered samples from the outcrop. Prior to age dating, extensive mineral characterization was carried out comprising petrography (TS, SEM, TEM) and XRD clay analyses. An undeformed host rock yields an age of 55 Ma (Paleogene-Eocene) and the Atera fault gouges clay ages range from 40 to 60 Ma (Paleogene-Eocene to Paleocene) and will be discussed within the geochronological and thermochronological background of the study area.