Three component geomagnetic anomalies in backarc basins (e.g. Japan Seq and Okinawa Trough)

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1. Geomagnetic three component anomalies in the Japan Sea(1) Japan Basin: Three component magnetic survey was conducted by R/V Hakuhomaru and R/V Tanseimaru of ORI of Univ. of Tokyo in June 1987. The detailed feature of geomagnetic anomaly lineations was revealed by the three component anomalies. One of the important results is that magnetization of the Japan Basin seafloor has the north-south declination which does not suggest rotation of the basin.(2) Yamato Basin: The magnetic survey over 4 seqmounts was conducted through the DELP program in summer 1986. The declinations of magnetization of all 4 seqmounts direct almost due north-south, which suggest no rotation of the basin.2. Geomagnetic three component anomalies in the Okinawa TroughIn the Iheya depressionm the central part of the Okinawa Trough there are large amplitude geomagnetic anomalies. These anomalies are explained by the seafloor topography with normal magnetization, which suggests that the magnetic source is the young intrusive volcanic rocks in the Brunhes epoch.3. OBM(Ocean Bottom Magnetometer) survey: An OBM with newly developed detach device was deployed in the north of Nankai Trough and withdrew by an acoustic detach system.