2006 Volume 2006 Issue 26 Pages 163-191
The 28-km-long surface ruptures of reverse fault type were associated with the 1945 Mikawa earthquake (Mj 6.8) in the southeastern part of Aichi Prefecture, central Japan. Two traces of surface faulting had appeared along the pre-existed late Quaternary faults named as the Fukouzu (ca 18 km long) and Yokosuka (ca 10 km long) faults, showing a hook-like complex shape with N-S and E-W trending sections. All the existing data concerning the 1945 ruptures have been compiled by Sugito and Okada (2004), and then this paper describes geomorphic and geologic features, characteristics of the faults, and relationship between surface rupture and Quaternary fault.
Based on trench excavation and boring exploration surveys recently carried out at several sites by the CRIEPI (Central Research Institute of Electric Power Industry), interpretation by detailed topographic maps and air photos, leveling of fault scarplets, and age estimation for the faulted terraces, characteristics of the seismic faults have been clarified. Average vertical slip rate for the Fukouzu fault are roughly measured to be 0.6 m to 0.9 m per one thousand of years. Recurrence time of the Mikawa earthquake type is estimated about 20,000 to 30,000 yearinterval. The Yokosuka fault is a subordinate fault with weaker topographic and geologic expression and has slightly lower slip rate than Fukouzu fault. Tectonic setting, geomorphological classification and underground structure etc. in this area are also discussed.
