VELOCITY MODEL OF THE ASTHENOSPHERE IN THE KURILE-KAMCHATKA REGION AND ADJACENT PARTS OF THE SEA OF OKHOTSK AND THE PACIFIC

Abstract

The asthenosphere of the Sea of Okhotsk is structurally very complex. The depth of its top edge, its thickness and its dip range, respectively, from 40 to over 250 km, from 35 to 160 km and from zero to 30°. We should emphasize, too, that the thickness and the dip of the asthenosphere under the Sea of Okhotsk vary both longitudinally and latitudinally. The asthenosphere is dead-ended in various places here, i.e., is a discontinuous layer. Its roof locally rises very high and, perhaps, is in contact with the Earth's crust. The complex asthenospheric structure described above occurs only under the central and southern parts of the Sea of Okhotsk. The asthenosphere is likely to have an equally complex structure in most other regions of high recent and present tectonic activity, for example in many tectonically active areas of the West Pacific margin.