Study for the Possibility of Earthquake Prediction by High density Geoelectric Potential Observations and its Theoratical Approach.

地电位场在地震前是否会出现异常变化是一个长期争论的问题。最近，货车小组报告了许多关于希腊地震的积极结果。为了验证他们的方法，在日本中部地区进行了类似的观测。我们在小松、水津（石川县）、富山（富山县），滨冈和清水（静冈县），Outaki（长野县），北藤（山梨县），和筑波和日立大宫（茨城县）一般认为日本是一个电力噪音很大的国家，因此这种类型的研究是不可能的。为了克服这种观点，我们在同一个站集中安装了短偶极子和长偶极子。例如，在筑波站，我们在9个月内仅用一对短偶极子就观测到了上千个异常，然而，应用两对偶极子，异常仅减少了50。此外，安装2km长的偶极子，异常只减少了一个。在我们的观测期间，1996年3月6日在山梨县东缘发生了一次5.8级地震。我们的北藤站距离震中20公里。在北藤站，我们只观测到1996年1月29日的一次异常变化。当时我们还没有安装一个长偶极子，因此人工噪声抑制效果不好。1996年8月，该研究的负责人访问了雅典大学，总结了我们的研究计划，并讨论了未来的研究计划。

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.