SAKAI Hideo Faculty of Science, Toyama University, Associate Professor, 理学部, 助教授 (30134993)
石渡 明 金沢大学, 理学部, 助教授 (90184572)
古本 宗充 金沢大学, 理学部, 助教授 (80109264)
河野 芳輝 金沢大学, 理学部, 教授 (80019489)
UYEDA Seiya Institute of Oceanic Research and Development, Tokai University, Professor, 海洋研究所, 教授 (60011459)
|Budget Amount *help
¥7,000,000 (Direct Cost : ¥7,000,000)
Fiscal Year 1996 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1995 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 1994 : ¥4,700,000 (Direct Cost : ¥4,700,000)
Whether the geoelectric potential field exhibits anomalous changes before earthquakes is a matter of long-standing debate. Recently many positive results have been reported for Greek earthquakes by the VAN group. To check their method, similar observations have been carried out in the Central Japan area. We established geoelectric potential monitoring stations at Komatsu, Suzu (Ishikawa Pref.), Toyama (Toyama Pref.), Hamaoka and Shimizu (Shizuoka Pref.), Outaki (Nagano Pref.), Kitafuji (Yamanashi Pref.), and Tsukuba and Hitachi-ohmiya (Ibaragi Pref.) during the Grant period.
It is generally claimed that Japan is a electrically noisy country, therefore this type of study is impossible. To overcome this opinion, we intensively installed both short and long dipoles in a same station. For example, at the Tsukuba station, we observed over thousand of anomalies for only one-pair of short dipole during nine months, however, to apply two-pairs of dipoles, the anomalies decreased only 50. Furthermore, to install 2km-long dipole, the anomaly decreased only one. It means appropriate dipole configuration works even in Japan.
During our observation period, on March 6,1996, we had an M5.8 earthquake at the eastern margin of the Yamanashi Prefecture. Our Kitafuji Station locates 20km apart from the epicenter. At the Kitafuji station, we observed only one anomalous change on January 29,1996. At that moment we had not yet installed a long dipole, therefore artificial noise rejection was not well. However this observation gives us a lot of useful information.
On August 1996, the head investigator visited Athen University to summarize our program and discussed a future research plan.