諏訪之瀬島の地磁気異常と3次元磁気構造

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書誌事項

タイトル別名
  • Aeromagnetic Anomalies and a 3D magnetic structure of Suwanose-jima Island
  • スワノセジマ ノ チジキ イジョウ ト 3ジゲン ジキ コウゾウ

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Airborne magnetic surveys of Suwanose-jima Island were conducted on August, 24 and 25, 1999 at the altitude of 1066m by a proton magnetometer installed on a craft of YS-11. Magnetic anomalies of total force are calculated by subtracting IGRF-10. The negative peak (-326nT) is observed over the north to northeastern coastal zone and a positive peak (242nT) is over the southeastern slope. Another positive peak is also recognized over the southern tip of Island. The volcanic edifice is approximated by the assemblage of the prismatic bodies for the 3D magnetic analyses. A 3D model analysis based on an uniform magnetization assumption shows the magnetization intensity of 3.14A/m corresponding to a magnetization direction polarized in the direction defined by declination of 0° and inclination of 42.5°. A 3D non-uniform magnetization analysis, where each block is magnetized in the same direction as in the uniform model with a variable magnetization intensity, is conducted to derive an internal magnetic structure of the edifice. This result makes it apparent that the volume weighted mean magnetization intensity is ranging from 2.87 to 3.12A/m, and a non-uniformity of magnetization from 40% to 14%, by taking into consideration of the base layer underlain by the volcanic edifice. Besides, the following features are also made apparent. (1) Relatively low magnetization zones (-0.5～-1.5A/m) are recognized in the southwest of Mt Ontake. This low magnetization zone extends to the base layer between 0m and 700m below sea level. This zone is thought to be linked with the conduit of Suwanose-jima Volcano. (2) Relatively strong magnetization zones (0.5～1.5A/m) are recognized in the southeast of the summit area and they further extend northeastward to the east offing of Suwanose-jima Island. (3) The base layer between 0m and 700m b.s.l. is generally small in magnetization intensity (-0.5～-1.5A/m) except the high magnetization zone denoted in 2). The above features may imply that the base layer is composed of more siliceous rocks than pyroxene andesites forming the present volcanic edifice.

収録刊行物

  • 火山

    火山 52 (4), 211-220, 2007

    特定非営利活動法人 日本火山学会

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