Three‐dimensional modelling of upper mantle structure under the Pacific Ocean and surrounding area

Abstract

Long‐period (75–250 s) fundamental‐mode Love and Rayleigh waves are inverted for the seismic velocity variations in the upper mantle under the Pacific Ocean and surrounding area. The data are inverted to map the regional variation of phase velocity, and then the velocity structure of the upper mantle. No a priori regionalization is used in this study, and the lateral heterogeneity is expanded horizontally into blocks (10°× 10°). To estimate the reliability of the velocity distribution, we have calculated the resolving kernels. In the central, NW, NE and SW regions, the resolving kernels have fairly sharp peaks. In the SE region, however, resolution is not so good. The results show good correlation with surface tectonics. In the velocity map, shields and ridges are the major features in the depth interval 50–100 km. Anomalies associated with the East Pacific Rise and the shields persist to 300 km. At 400 and 500 km, high‐velocity anomalies appear under the eastern and southern Pacific ridges, and a low‐velocity anomaly appears beneath Australia. The present study provides better resolution than previous studies because of the better path coverage. For example, a large low‐velocity anomaly emerges under Hawaii down to the depth of 200 km for SH velocity. The horizontal extent of this anomaly is comparable to the size of the Hawaiian swell. This feature supports that the Hawaii hotspot is an isolated, truly anomalous feature in the Pacific Ocean. Copyright © 1989, Wiley Blackwell. All rights reserved