A magnetic anomaly map in the Japanese region with special reference to tectonic implications.

Abstract

Aeromagnetic surveys over the Japanese Islands yielded a detailed magnetic anomaly map. Magnetic anomaly maps were also derived for sea regions surrounding the Japanese Islands from ship-borne magnetic surveys. We combined these maps into a unified magnetic anomaly map for the entire Japanese island arc region. The map enables us to find some characteristic features; in particular, three similar anomaly belts are clearly recognized. We attempted to combine these belts into one linear belt, although they are spatially separated and the direction of elongation is different from one belt to another. This process requires rotations of the blocks constituting the Japanese Islands. The result of our reconstruction of the blocks agrees with the result derived from paleomagnetic studies, supporting the opening of the Japan Sea. This implies that magnetic anomalies serve as markers for the original locations of blocks, in a sense similar to yet slightly different from oceanic magnetic lineations in plate reconstruction.