A Magnetic Anomaly Map of the Japan Sea

抄録

A magnetic anomaly contour map (contour interval is 50nT) is compiled with all the available data of the total intensity of geomagnetic field. Data are very dense in the coastal areas of the Japanese islands so that contour control is good while in the coastal areas of U. S. S. R. and the Korean Peninsula, data are not so dense. The amplitudes of anomalies are generally small compared with that in the northwestern Pacific Ocean. The magnetic anomaly lineations exist in the southern half of the Japan Basin. From identification of the lineations, the Japan Basin stopped opening 15Ma BP on the assumption of two-limbed opening and the spreading rate of 3.4cm/yr. There are many seamounts and uplifts which have anomaly patterns suggesting their reversed magnetization. This seems to be a crucial point towards understanding the tectonics of the Japan Sea.