ESR dating of geological fault with a new isochrone method granite fractured on the earthquake in 1995

A new ESR isochrone dating for fracture age based on the effective annual dose for different grain sizes has been applied to quartz grains in fractured granite at the Nojima fault that moved during the earthquake in 1995 and in fault gouge at the Rokko fault in the vicinity. Incomplete resetting of ESR signals was observed for both samples collected at the ground surface. The fracture age of the quartz grains was obtained for the Rokko fault as (1.6 ± 0.2) × 105 yr. At the Nojima fault there appears to be a considerable effect from previously-fractured surfaces in the newly-fractured material. The relation between the fracture age and the age of the fault movement is discussed.