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Science 3 December 1999:
Vol. 286. no. 5446, pp. 1925 - 1928
DOI: 10.1126/science.286.5446.1925
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Reports

Complex Shear Wave Velocity Structure Imaged Beneath Africa and Iceland

Jeroen Ritsema, 1* Hendrik Jan van Heijst, 1 John H. Woodhouse 2

A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle.

1 Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA.
2 Department of Earth Sciences, Oxford University, Oxford OX1 3PR, UK.
*   To whom correspondence should be addressed. E-mail: jeroen{at}gps.caltech.edu

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