Institution: | Centre de Recherche en Géophysique, École des Mines de Paris, 35 rue St Honoré, 77 305 Fontainebleau, France. E-mail:; Usu Volcano Observatory, Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Sobetsu-cho, Hokkaido 052–0103, Japan. E-mail: |