地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
東海沖の海底地電位変化について
海底地震常時観測システムの利用
森 俊雄
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ジャーナル フリー

1982 年 35 巻 2 号 p. 213-221

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Electric field on the sea-floor have been observed by making use of the electric powerfeeding arrangement for the submarine system which was laid off the Tokai-oki, south coast of Chubu district, Japan. The submarine system consists of four seismographs and a tsunami-meter, and each instrument is in series through a submarine co-axial cable with the shore station (Omaezaki weather station). The direct current transmitted from the power supplier goes through the inner conducter of the submarine cable, and is released from the sea earth attached near the terminal apparatus, and sends back to the shore earth through the sea water and floor. As the direct current remains constant, the change in the supply voltage is equal and opposite in polarity to the extraneous voltage between the sea earth and the shore earth in distance of 110km.
It has been preliminary reported that the supply voltage had repeated the daily change with the amplitude of about 0.1 volt and the pattern was similar to the change in the geomagnetic field. In this paper, at first, the fluctuations in the supply voltage are compared with the geomagnetic and geoelectric fluctuations on land in detail. It is confirmed that the changes in the supply voltage express the charge in the submarine electric field which are mainly caused by geomagnetic fluctuations.
Anomalous changes of the supply voltage were recognized before and just after the Izuhanto-tohooki earthquake on June 29, 1980 with magnitude 6.7. One of the anomalous changes is the cluster of pulse-like changes from about 17 hours to about 20 minutes before the occurrence of the earthquake. Another is a concurrent bay-like change with the earthquake. These anomalous changes seem to be related with the earthquake.

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© 社団法人日本地震学会
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