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Evidence for a chemical-thermal structure at base of mantle from sharp lateral P-wave variations beneath Central America

  1. Xinlei Sun *,
  2. Xiaodong Song * , † , ‡ ,
  3. Sihua Zheng † , and
  4. Don V. Helmberger ‡ , §
  1. *Department of Geology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
  2. †Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China; and
  3. §Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125

  1. Contributed by Don V. Helmberger, October 23, 2006 (received for review May 18, 2006)

Abstract

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.

Footnotes

  • ‡To whom correspondence may be addressed. E-mail: xsong{at}uiuc.edu or helm{at}gps.caltech.edu

  • Author contributions: X. Song and D.V.H. designed research; X. Sun and X. Song performed research; X. Sun and S.Z. analyzed data; and X. Sun, X. Song, and D.V.H. wrote the paper.

  • The authors declare no conflict of interest.

  • This article contains supporting information online at www.pnas.org/content/full/0609143103/DC1.

  • Abbreviations:
    CC,
    cross-correlation coefficient;
    CSN,
    China Seismograph Network.

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