1. Graduate School of Engineering, Osaka University, 2‐1, Yamada‐oka, Suita 565‐0871, Japan, hata@civil.eng.osaka-u.ac.jp
2. Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611‐0011, Japan, goto@catfish.dpri.kyoto-u.ac.jp
3. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1‐1‐1 Higashi, Tsukuba 305‐8567, Japan, yoshimi.m@aist.go.jp