オホーツクプレート運動の地球物理学的検証とそのテクトニクスの研究

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To clarify the movement of Okhotsk Plate a new GPS network have been deployed in Kamchatka, Sakhalin and Khabarovsk from 1996 to 1998. The network consists of 12 stations that have been operating continuously at each point as possible. Existence of Okhotsk Plate is clearly concluded by analyzing the data obtained till the end of 1998. Furthermore existence of Amur Plate and its velocity vector which has been assumed nearby Okhotsk Plate by several authors based on geological and seismological data are also quantitatively determined by this project. Velocity vector of south Sakhalin obtained, here shows that the collision boundary between Okhotsk and Amnur Plates is located on inland of southern Sakhalin and northern Hokkaido instead of the former assumed zone located at the eastern margin of Japan Sea. The collision rate determined is about 2 cm/y that is two times greater than the former estimations.In the sourece region of the 1995 North Sakhalin Earthquake temporal seismic observations were carried out every summer since 1996. The characteristic property of b-value distribution on the fault plane was found and interpreted by the differences of strength of the stress field. In the South Sakhalin seismic belt trending North-South is clearely exposed. This may be the boundary between Okhotsk and Amur plates. GPS network in Kmachatka was deployed in 1996 and 1997 and will provide eough data in time and space for detail analysis to define the movement of Okhotsk plate.