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タイトル: 1980年伊豆半島東方沖地震と伊豆船原,柿木における水位変化の異常
その他のタイトル: Changes in Water Level at Funabara and Kakigi before the Izu-Hanto-Toho-Oki Earthquake of 1980
著者: 山口, 林造
著者(別言語): Yamaguchi, Rinzo
発行日: 1981年3月31日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第55冊第4号, 1981.3.31, pp. 1065-1071
抄録: An earthquake with magnitude 6.7 occurred off the eastern part of the Izu Pe ninsula at 16 h 20 m on June 29, 1980. The earthquake was the largest one of the swarm which started on June 24 and centered nearly 30 km east from the recording wells at Funabara and Kakigi in the Izu Peninsula. Measurements of the ground water level of deep wells have been made at Funabara and Kakigi since September 1976. The depths of the two wells are 600 m and 250 m respectively. In the record we can see small fluctuations with the earthquake. These fluctuations are presumed to result from compression and expansion of elastic confined aquifers by the passage of earthquake waves. After these small fluctuations falls of about 40 cm and 10 cm were recorded in the water levels at the respective wells associated with the earthquake. These wells have also showed remarkable coseismic drops of about 7 m and 1.5 m in connection with the Izu-Oshima-kinkai earthquake of January 14, 1978. Remarkable changes in water level can be seen in the records at Funabara. The earthquake occurred about a month after a slow variations trend in water level changed to rapid rising. Precursory changes as observed at Funabara could not be detected at Kakigi. This may be partly because a shallow well tends to keep a constant water level. As mentioned in a previous report, the water level affected by rainfall returns rapidly to the previous level and hence relatively slow variations of pore pressure (or originally of tectonic stresses) do not appear on the records. Therefore we believe that a deep well is more suitable than a shallow well for detecting precursory phenomena of an earthquake.
URI: http://hdl.handle.net/2261/12785
ISSN: 00408972


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