N.I. PAVLENKOVA (IPE RAS), S.N. KASHUBIN (VSEGEI), L.I. GONTOVAYA (IVS FEB RAS), G.A. PAVLENKOVА (IPE RAS)

Deep structure and geodynamics of the Sea of Okhotsk region

The new deep seismic sounding (DSS) in the Okhotsk Sea and a generalization of other geophysical data in this region allow to solve many geodynamic problems on the structure of the earth’s crust and the upper mantle of this continent – ocean transition zone. Two DSS profiles, made with а very detailed system of observation, finally decided the problem of the Okhotsk Sea crustal type: it is a typical continental crust with a thick granite­gneiss layer. The thin crust of the sub­oceanic type is distinguished only in the narrow basin near the Kuril Islands. The upper mantle velocity models along the DSS profiles are also similar to the continental models. A comparison of the Kuril­-Kamchatka deep earthquake focal zone with the upper mantle velocity model of the North Eurasia shows the Okhotsk-­Kamchatka region has the lithosphere structure of the Asian continent with some local changes only in the upper 100 km depth. The new important structural element of the Okhotsk Sea is the deep fracture zone along the Sakhalin Island. This zone is traced far to the Pacific Ocean and in the Asian continent.
Keywords: deep seismic studies, Earth’s crust, upper mantle, Sea of Okhotsk, earthquake focal zone, deep mantle faults, geodynamics.