In November 2005, we conducted the first low-altitude, high-density helicopter-borne aeromagnetic survey
over Sakurajima Volcano, Kyushu, Japan to provide a baseline for subsequent measurement of changes in
magnetic anomalies related to volcanic processes, because previously acquired aeromagnetic data cannot
resolve small-scale geological feature. Although the observation error was considered to be b10 nT, the
harmonic component is extracted by the reduction procedure. We applied an apparent magnetization
intensity mapping method to the newly obtained aeromagnetic data assuming that magnetization intensity
varies only laterally. Results showed the following features: (1) Apparent magnetization intensities of lava
flows were from 4.0 to 6.0 A/m. The most remarkable highs (N5.0 A/m) were located on the lava around
An'ei craters and on the northeastern flank of Kita-dake, (2) the lowermost values of apparent magnetization
(b2.0 A/m) are locally distributed around the active craters of Minami-dake, suggesting high temperature in
the shallow part and (3) apparent magnetization lows (~2.5 A/m) lie over the northwestern flank of Kitadake,
reflecting debris flows and/or volcanic fans. To examine the validity of the obtained map, we carried
out rock-magnetic studies. The total magnetization intensities for the surface-rocks showed reasonable
correlation with the mapped values.
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