1. Civil Engineering Research Laboratory, Central Research Institute of Electrical Power Industry, 1646 Abiko, Abiko City, Chiba Prefecture 270-1194, Japan.
2. Corresponding author.
3. Institute of Seismology and Volcanology, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan.
4. NeoScience Co., 5-11-22, Onosato, Sennan, Osaka 590-0526, Japan.
5. Geotechnical Center, Oyo Co., 2-61-5 Toro, Saitama 331-8688, Japan.