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The Shikoku Basin is a backarc basin occupying the northern part of the Philippine Sea Plate. The recent Continental Shelf Survey Project of Hydrographic Department, Maritime Safety Agency of Japan reveals interesting features of the basin genesis. High-resolution magnetic data of whole basin and the adjacent region are presented together with the topographic and seismic data. Based on detailed mapping of magnetic anomalies and topography, we propose a scenario of evolution of the Shikoku Basin from 30 Ma to 15 Ma. The history of Shikoku Basin is divided into five stages as follows-rifting, NNW-SSE opening, N-S opening, NW-SE opening, and volcanism and deformation after opening. Some dipole-type anomalies which are not accompanied by any topographic highs are distributed in the vicinity of both sides of the basin. They are considered as the effect of the upwelling of magma during the rifting stage. In addition, we recognize the structures deformed after opening in the northern part of the basin.
Okino et al. (Sat,) studied this question.