北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University;第70号

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ドーム状隆起に伴う磁場変化 ―有珠山2000 年噴火時の全磁力変化再検討―

橋本, 武志;茂木, 透;西田, 泰典;高田, 真秀;鈴木, 敦生;前川, 徳光;佐藤, 秀幸

Permalink : http://hdl.handle.net/2115/20428
JaLCDOI : 10.14943/gbhu.70.123

Abstract

We investigated geomagnetic changes due to dome-like deformation by using a truncated circular cone model. In the case of the normal magnetization, magnetic total field decreases in the northern side of the uplift center, while it increases in the southern side. We found that the original topography prior to the mound formation does not affect the pattern of this magnetic change. We then apply this calculation to the mound-forming activity in the 2000 eruption of Usu Volcano to infer the magnetic change on the foot of the mound. The expected range of magnetic total field change at the station U01 is -80 to -800 nT which is in the opposite sense to the observed actual change (+70 nT). We examined some alternative mechanisms to compensate this decrease due to the deformation. None of them, however, can be a promising candidate. The most reasonable explanation so far for this contradiction is the reversed magnetization of the Tertiary lava that may comprise the mound.

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