A study of the northwestern Pacific upper mantle

Abstract

Records obtained with a bottom-mounted hydrophone at Wake Island are used in this study for an analysis of P and S waves originating from the Marianas Islands, Japan, and the Southern Kurils Islands. Because the distances for these areas range from 18 degrees for the Marianas to 30 degrees for the Kurils, P and S arrivals at Wake are ideal for studying the effect of the "20-degree discontinuity". The objective of the study was to obtain evidence for the low-velocity channel below the Northwestern Pacific on the basis of P and S arrivals at Wake from the above-mentioned areas. If adequate evidence were found, it was hoped that the data might permit the boundaries of the channel to be established from an analysis of the observed velocities as a function of distance and depth.