Cooperative research among Japan, Russia and Korea in crustal structure in transient areas between land and ocean around Japan Sea

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Japan Sea, which is a back-arc basin in the northwestern Pacific, is located between Asian continent and Japanese islands. It comprises the Japan Basin in the north and northwest, the Yamato Basin in the southeast, and the Tsushima Basin in the southwest. Three deep basins comprise the Japan Sea ; they are separated by rifted continental remnants such as the Korea Plateau, Oki Bank, and Yamato Bank. The opening of the Japan Sea was initiated by crustal thinning in the northeastern Japan Basin in Early Oligocene, followed by seafloor spreading in the Late Oligocene. During initial spreading of the Japan Basin, and later one of the southern Japan Sea there underwent crustal extension, forming the Yamato and Ulleung Basins. In the Late Miocene, changes in plate motions and subduction mode along the subduction zones, east and southwest of Japanese Islands, caused bark-arc closing and crustal shortening that has continued till the present. We have conducted the OBS (Ocean Bottom Seismometer) experiments, magnetic and gravity surveys, and single air-gun survey to make clear the crustal structure in the transient area between land and ocean. As the result, we got the mixed structure with oceanic and continental ones, and understood importance of magnetic anomaly information obtained at near bottom using DTCM which will lead us smoothly to confirm the result.