Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6, Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
Department of Earth Sciences and Insititute of Geophysics, National Central University, 300, Jhongda Rd., Chung Li, 32054 Taiwan