Ömer Aydan, University of the Ryukyus, Okinawa, Japan, Takashi Ito, Tohoku University, Sendai, Japan Takafumi Seiki, Utsunomiya University, Japan, Katsumi Kamemura, Fukada Geological Institute, Tokyo, Japan Naoki Iwata, Chuden Engineering Consultants Co., Ltd., Hiroshima, Japan