3D S-Wave Velocity Model of the Crust and Upper Mantle beneath the Sea of Okhotsk and the Kamchatka Peninsula

Abstract

A 3D S-wave velocity model (from 0 to 350 km depth) is determined for the region of the Sea of Okhotsk and the Kamchatka peninsula, through Rayleigh wave analysis applied to the traces of 278 earthquakes registered by 12 seismic stations, both located within (and nearby) of the study area. This model reveals the principal geological and tectonics features present in the study area, e.g., the presence of two lower-crust hot plumes located at the northwest of the Sea of Okhotsk, which are shown as two zones of low S-wave velocity (from 20 to 30 km depth). Also, a conspicuous low S-wave velocity zone is determined at the southwest of the Sea of Okhotsk (from 35 to 60 km depth), which can be matched up with a high conductivity layer previously determined from 30 to 65 km depth. For the Kamchatka peninsula, low S-velocities are determined beneath the volcanic belt from the upper crust (~5 km-depth) down to a depth of ~60 for the southern part, and down to a depth of ~140 km for the northern part. This low S-wave velocity pattern is enlarged in size at the northwest (north of ~55°N), following the location of the Kliuchevskoi and Sheveluch volcanoes, which confirms that these volcanoes must be a part of the same subduction-induced volcanic process. The present model shows that the subducting Pacific slab terminates near to the Aleutian-Kamchatka junction, i.e., no relict slab underlies the extinct northern Kamchatka volcanic arc. This model shows that this slab shoals towards north, and there exists a gap associated with the loss of this slab beneath Sheveluch and Kliuchevskoi volcanoes. The low S-wave velocity pattern determined at northwest of the slab edge confirms the presence of the asthenospheric flow, which would pass through this gap to the northwest around the north slab edge. Finally, the present model shows the precise location and detailed structure of the asthenosphere, which is a new result that has not been determined in other previous studies.