1982年7月23日茨城県沖地震(M=7.0)に伴った津波について,検潮記録で調査した.波源域は水深1,000mと3,000mの範囲に長さ60kmと推定され,余震域とは南西方向に約30kmずれている.津波マグニチュードはm=0とみなせる.茨城・房総沖の津波活動と比べ,35°～36°Nの範囲の千葉県東方沖の活動がきわめて低調である.この海域は,津波発生の空白域として注目すべきであろう.
Based on tide-gauge records, the tsunami magnitude and the source area of the Ibaraki-oki tsunami on July 23, 1982 and past tsunamis off the eastern coast of the Kanto region, eastern Japan, since 1896 are investigated. At the tidal stations from Onahama to Choshi, the initial disturbance of the present tsunami began with an upward motion about 30min after the earthquake occurrence. The first wave period was 10 min and the first or second waves were the highest with a double-amplitude of 13-26cm. The tsunami magnitude on Imamura-Iida scale is estimated to be m= O. This is average for an earthquake having a magnitude of M=7.0. The source area of tsunami estimated by means of an inverse refraction diagram is 2.2×10^3 km2, extending 60 km between the bathymetric contours of 1,000 m and 3,000 m. Since 1896, many tsunamis were generated off Fukushima and Ibaraki Prefectures, and the source area of the present tsunami was located at the southern end of the 1938 Fukushima-oki tsunamis. In contrast to the tsunami activity in the Fukushima-Ibaraki region, a tsunami (seismic) gap exists east off the Boso Peninsula between 35° and 36°N. It should be considered a region of tsunami risk, because the historical large tsunami (m=3) of Nov. 4, 1677 was generated near the trench.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
58
号
2
ページ
423 - 431
発行年
1983-10-22
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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16. 1982年茨城県沖津波とその周辺海域の津波活動
ji0582006.pdf
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