Structure and Evolution of the Lithosphere in the Ocean-Continent Transition Zone.

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We studied structure and evolution of the Lithosphere in the ocean-continent boundary zne in the southwestern part of the Japa Sea. We conducted a geohysical experiment in the Tsushima basin including seismic and geomagnetic measurements in 1992. An analysis f the data revealed the crusta and uppermost mantle structure in the Tsushima and Yamato basins and the northern part of the Kita-oki bank. Te Tsushima basin has a similar crust t that in the Yamato basin : both basins have a 14-km-thick crust, which is twice as thick as an average oceanic crust. On the contrary, the transition zone from the Ts4sh50a bas5n t6 the Ya0at6 bas5n, where 5s a sha336w water between the Yamato banks, has a 24-km thick crust. The veocity distribution in the crust indicates a continental characteristic including a 6-km/s layr. Electromagnetic observation using three ocean bottom electro-magnetometers resulted in that the specific electric resistance beneath the Tsushima Basin is less than that beneath the Japanese Islands and the Koren Penisula mainly due t presence of a lot o free water in the crust and that there needs no conducte in the upper mantle shallower than 160km taking the first dimensional mdelling into account.