The Philippine Sea: New survey results reveal the structure and the history of the marginal basins

The Hydrographic Department of Japan initiated a long-term geological and g eophysical survey of the Philippine Sea in 1983. We here summarize the bath ymetry and magnetic anomalies of this area, focusing on the structure and t he evolutionary process of the marginal basins. The Shikoku and Parece Vela Basins developed as one backarc system in the later phase of their formati on; the significant difference between the two basins, however, is dearest near the extinct spreading centers. The steep Oki-Daito Escarpment, located in the northern West Philippine Basin, was mapped for the first time durin g this survey. The N-S trending spreading fabric north of the escarpment is in striking contrast to the NW-SE to E-W lineament in the south. Our data reveal a more complicated history of the western Philippine Sea than has be en proposed in previous studies.