Magnetic Model of the Izu-Oshima Island and its Surroundings Estimated from the Aeromagnetic Anomaly

Abstract

The aeromagnetic anomalies over the Izu-Oshima Island and its surroundings were interpreted using 3-D magnetic inversion analysis.
A magnetic positive anomaly extends from the south of Oshima to the neighboring off-shore area trending northwest by west. Taking the previous rock-magnetic studies into consideration, the magnetic anomaly in the Oshima Island is caused by igneous rocks having high remanent magnetizations. Calculation shows that the observed anomaly can be interpretedwell by the effect of topography over the Oshima Island except for neighboring off-shore area.
The thick magnetic layer trending NWW-SEE direction around the Oshima Island was suggested by the iterative inversion. The distribution of the thick magnetic layer coincides with the NW-SE trending dike distribution and the NWW-SEE trending alignment of submarine volcanoes. This indicates that the observed magnetic anomaly is associated with the subsurface volcanisms of the island. According to the comparison between the observed anomalies and the calculated anomalies caused by topographic relief, and the geometry of thick magnetic layer, the high magnetic anomaly around the Oshima Island includes the effect not only of surface volcanics but of a number of high magnetized concealed intrusives underneath.