Structure and Tectonics of Japan Sea and Sikhote Alin and their relation to Japan Arc

l.在日本海盆的研究在这项合作研究期间，POI的Gagarinsky教授R/V在俄罗斯专属经济区内日本海盆整个地区每隔5英里的轨道上进行了海洋调查。a.地震调查：日本盆地的地震研究采用了千叶大学的OBS和P01的单气枪，结果表明，日本盆地中部地壳厚度为8- 9 km，其中沉积物厚度为1.5km，并向东递增。地壳特征与典型的大洋地壳特征并不完全相同，盆地东部地壳为大洋地壳，则盆地中部具有与东部不同的发育模式，即海底扩张发育。B.磁法调查：POI质子旋进磁力仪和STCM利用千叶大学的船用三分量磁力仪对该盆地进行了磁性研究，结果表明，该盆地东部有明显的磁异常线理，而中部则不明显。这与上述地震调查是一致的。c.重力调查：使用了POI的船上重力仪。从重力异常得到的地壳结构从东到西从海洋到大陆变化。2. Sikhote Alin（地质研究）地质调查是利用Sikhote Alin特别是Tercialy时间的地质资料，重建日本海开放前日本岛屿的原始位置。第三纪时日本诸岛和Sikhote Alin之间的地质连续性被揭示出来，同时考虑到其他数据，即盆地底部的地形和日本岛弧的变形。

l.Research in the Japan BasinDuring this cooperative research, the marine investigations had been carried out by R/V Prof.Gagarinsky of POI on the tracks of 5 mile interval in the whole area of Japan Basin in the Russian EEZ..a.Seismic investigation : OBSs of Chiba University and the single air-gun of P01 were used for the seismic research in the Japan Basin resulting in that the thickness of crust in the central part of the Japan Basin is 8-9km including 1.5km thick sediments and increasing towards east. The feature of crust is not completely identical with the typical oceanic one.The crust in the eastern part of the Basin is oceanic, then the central part of the Basin has the different developing mode from the east part, namely sea floor spreading development.b.Magnetic investigation : A proton precession magnetometer of POI and a STCM(Shipboard Three Component Magnetomete) of Chiba Univ. were used for the magnetic study of the Basin resulting in that there are clear magnetic anomaly lineations in the eastern part of the Basin and not so clearly in the cental part. This is coincident with the seismic investigation mentioned above.c.Gravity investigation : A shipboard gravimeter of POI was used. The structures of the crust obtained from gravity anomalies change from the oceanic to the continental from east to west.2.Research in the Sikhote Alin (Geological Research)The geological investigation was done to reconstruct the original position of Japanese islands before opening of the Japan Sea using the geological data in the SikhoteAlin especially of Tercialy time. The geological continuation between the Japanese islands and the Sikhote Alin in the Tercially time was revealed taking other data, that are, tobography of the Basin floor and deformation of the Japanese Island Arc into account.