Geomagnetic Total Force Investigation around the Epicenter of the 1984 Western Nagano Prefecture Earthquake

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  • MURAKAMI Hideki
    Department of Geology, Faculty of Science, Kochi University
  • YAMADA Isao
    Department of Earth Sciences, School of Science, Nagoya University
  • FUJIMURA Akio
    Department of Earth Sciences, School of Science, Nagoya University

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Other Title
  • 1984年長野県西部地震の震央周辺における全磁力調査
  • 1984ネン ナガノケン セイブ ジシン ノ シンオウ シュウヘン ニ オケル

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Abstract

The geomagnetic total force survey using a proton magnetometer was carried out around the epicenter of the 1984 Western Nagano Prefecture Earthquake (1984. 9. 14, M 6.8) in December 1984 and December 1985. Geomagnetic anomalies ranging from -200 to -500 nanoteslas were observed along the southern boudary of the aftershock region. It is considered that these negative anomalies reflect the crustal structure around the earthquake fault extending to N70°E direction. Obseved anomalies reveal that there is the vertical contact separatig layers of differig magetic susceptibilities at the depth deeper than several ten meters. The magnetic susceptibility of the layer lying south of the contact is 0.002 to 0.005 lager than that of the layer lying north. The vertical contact is 100 to 200 meters thick.<br>Changes of a few nanoteslas were observed during the period from December 1984 to December 1985. However, further study is necessary to conclude whether these changes were associated with the earthquake because the accuracy of diurnal correction was still not satisfactory.

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