Surface rupture associated with the 1945 Mikawa earthquake

Abstract

We have compiled all the existing data about geomorphic and geologic features of the surface rupture associated with the 1945 Mj 6.8 Mikawa earthquake, which struck the eastern part of Aichi Prefecture, central Japan. The 28-km-long surface trace of the rupture, including a 10-km-long submarine section in Mikawa Bay, showed a hook-like complex shape that consisted of three sections: two N-S-trending sections comprised of the northern 7-km-long section and the southern 14-km-long section, and the other section, extending for 7 km from east to west between the two N-S-trending sections. On the basis of the compiled data and reconstructed slip distribution along the surface rupture, we suggest that 1) nearly pure thrust faulting along the southern N-Strending section was predominant among the whole surface faulting during the earthquake,2) probably, this thrust faulting was a result of E-W to ENE-WSW-trending compressional stress in the upper crust, and 3) the E-Wtrending section behaved itself as a kind of tear fault, which was an oblique-slip reverse fault associated with the nearly pure reverse faulting along the two N-S-trending sections. The maximum amount of vertical offset was approximately 200 cm.
The source fault model constructed by Kikuchi et al. (2003) includes two asperities, and the northwestern asperity covers a wider area and exhibits a larger amount of slip than the southeastern asperity does. This doesn't agree with the 1) above. Further investigations are needed to understand what causes the discordance.