Affiliation: | Department of Physics, Faculty of Science, Mahidol University, Rama VI Rd, Rachatawee, Bangkok, 10400,;Thailand. E-mail: College of Oceanic and Atmospheric Science, Oregon State University, Corvallis, OR 97331,;USA. E-mail: Earthquake Research Institute, University of Tokyo, 1-1-1;Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. E-mail: |