YAMASAKI, Yuko, Dept. Earth Env. Sci., Grad. Sch. Sci. Tech, Kumamoto Univ, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 8608555, Japan, sk2atom@yahoo.co.jp and ISOBE, Hiroshi, Dept. Earth Env. Sci., Grad. Sch. Sci. Tech, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 8608555, Japan