1. Fukushima Museum, 1-25, Jyoto Machi, Aizuwakamatsu City, Fukushima 965-0807, Japan
2. INPEX Corporation, 5-3-1 Minato Ward, Tokyo 107-6332, Japan
3. Research Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Ibaraki 305-8567, Japan
4. Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan (e-mail: )