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PHYSICAL SCIENCES / GEOPHYSICS
Evidence for a chemical-thermal structure at base of mantle from sharp lateral P-wave variations beneath Central America
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*Department of Geology, University of Illinois at Urbana–Champaign, Urbana, IL 61801; Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China; and Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125
Contributed by Don V. Helmberger, October 23, 2006 (received for review May 18, 2006)
Compressional waves that sample the lowermost mantle west of Central America show a rapid change in travel times of up to 4 s over a sampling distance of 300 km and a change in waveforms. The differential travel times of the PKP waves (which traverse Earth's core) correlate remarkably well with predictions for S-wave tomography. Our modeling suggests a sharp transition in the lowermost mantle from a broad slow region to a broad fast region with a narrow zone of slowest anomaly next to the boundary beneath the Cocos Plate and the Caribbean Plate. The structure may be the result of ponding of ancient subducted Farallon slabs situated near the edge of a thermal and chemical upwelling.
core–mantle boundary | slab
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/content/full/0609143103/DC1.
To whom correspondence may be addressed. E-mail: xsong{at}uiuc.edu or helm{at}gps.caltech.edu
© 2007 by The National Academy of Sciences of the USA
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