Affiliation: | Department of Earth Sciences, College of Integrated Arts and Sciences, Osaka Prefecture University, Gakuen-cho 1-1,;Sakai, Osaka 599-8531, Japan. E-mail: Mizunami Underground Research Laboratory, Tono Geoscience Center, Japan Nuclear Cycle Development Institute, 1-63,;Yamanouchi, Akeyo-cho, Mizunami, Gifu 509-6132, Japan. E-mail: |