Velocity sections of the upper mantle under oceanic trenches

Abstract

According to the travel time of longitudinal waves from earthquakes in the upper mantle under oceanic trenches, a velocity model of waves beneath these structures to a depth of 360 km is developed. A sharp contrast to the distribution of V_p under the trenches of ocean regions studied earlier is found. Experimental data on the Kamchatka and Kuril trenches compiled by the authors do not allow the construction of a hodograph that would characterize such different speed sections. As a result of the selection process, the hodograph must correspond to the velocity profile different from that forming the pilot hodograph by no more than a few hundredths of km/s. In the depth interval 120–360 km, the velocity model is almost the same as the model for the mantle of a continental platform. At shallower depths, the velocity is lower, but it does not indicate the partial melting.