Aeromagnetic surveys over Izu-Oshima Volcano before and soon after the 1986 eruption.

An aeromagnetic survey over Izu-Oshima Volcano had been conducted in 1978 by the Geological Survey of Japan. A similar survey was carried out by Nakanihon Air Service Co. Ltd. on November 29-30, 1986 soon after the eruption. Comparison of those results revealed a very good repeatability of the magnetic anomaly pattern. It was suggested that the difference between the 1978 and 1986 anomaly maps was caused by the insufficient line spacing of each survey, and that there was no largescale variation in the magnetic anomaly. Then, both the survey data were processed together to produce a more detailed anomaly map, and a magnetic structural model was proposed from the analysis of the anomalies.