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Published 1987 | Published
Book Section - Chapter Open

Global Mapping of the Uppermantle by Surface Wave Tomography


Surface wave tomography compliments detailed body wave studies by providing a global framework for the lateral variability of the uppermantle. In particular the method allows one to map the mantle beneath the lithosphere and to discuss the fate of overridden oceanic plates. Midocean ridges appear to extend to at least 400 km. By contrast, the very high velocities associated with shields are primarily much shallower. The Red Sea-Afar region is a pronounced and deep low-velocity anomaly. A significant uppermantle anomaly has been found in the central Pacific. This "Polynesian Anomaly" is surrounded by hotspots; Hawaii, Tahiti, Samoa and the Caroline Islands. This may be the site of the extensive Cretaceous volanism which generated the plateaus and seamounts in the western Pacific. Anisotropy indicates deep upwellings, >300 km depth, under midocean ridges, the Afar and the Polynesian Anomaly and downwelling under the western Pacific and the northeastern Indian Ocean. The large fast anomaly under the south Atlantic may represent overridden Pacific plate.

Additional Information

© 1987 by the American Geophysical Union. I gratefully acknowledge the work of my colleagues Ichiro Nakanishi, Henri-Claude Nataf and Toshiro Tanimoto which forms the basis of the present paper. The figures were prepared by C. Stork. This research was supported by the National Science Foundation EAR-8115236 and EAR-8317623, and the National Aeronautics and Space Administration NSG-7610. Division of Geological and Planetary Sciences of the California Institute of Technology contribution number 4189.

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