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| | Abstract | | Total geomagnetic and topographic surveys in and around the Beyonnaise knoll volcano, which is located on the western margin of active arc (volcanic front), Izu-Ogasawara island arc, were conducted by Japan Marine Surveys Association (JAMSA) as a part of SIP in January, 2015. The geomagnetism was investigated by using a sea surface ship and a deep-tow which was towed between the depths from 200 m to 500 m. The topography was surveyed by a multi-beam echo sounder (MBES) from the sea surface ship. The 3-D magnetic inversion study revealed that the lower part of the Beyonnaise Knoll was composed of a high magnetization more than 6 A/m. The upper part was composed of weak-magnetization (around 1 A/m) for the most part, but a relatively strong part (2~3 A/m) was interspersed among the weakness. And it was also shown that the magnetizations of the central cone and a large hydrothermal deposit (Hakurei thermal deposit) were very low (less than 1 A/m). |
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