1. Graduate School of Science and Technology; Shizuoka University; Suruga-ku, Shizuoka Japan
2. Faculty of Education; University of the Ryukyus; Nishihara, Okinawa Japan
3. Department of Physics and Earth Sciences, Faculty of Science; University of the Ryukyus; Nishihara, Okinawa Japan
4. Institute of Geology and Paleontology, Graduate School of Science; Tohoku University; Aobayama, Sendai Japan