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

日本海位于亚洲大陆和日本岛屿之间，是太平洋西北部的弧后盆地。它包括北部和西北部的日本盆地，东南部的大和盆地和西南部的对马盆地。三个深盆地组成了日本海；它们被分裂的大陆残余隔开，如朝鲜高原、冲绳浅滩和大和浅滩。日本海的开放始于渐新世早期日本盆地东北部的地壳减薄，随后是渐新世晚期的海底扩张。在日本盆地的最初扩张期间，以及后来的日本海南部，那里经历了地壳的伸展，形成了大和盆地和宇梁盆地。晚中新世，日本群岛东部和西南部俯冲带板块运动和俯冲方式的变化导致了树皮弧闭合和地壳缩短，这种现象一直持续到现在。我们进行了海底地震仪(OBS)实验，磁力和重力测量，以及单气枪测量，以弄清陆地和海洋过渡区域的地壳结构。结果得到了洋陆混合构造，并认识到了利用DTCM获得近海底磁异常信息的重要性，这将使我们顺利地确认这一结果。

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.