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Science 23 October 1998:
Vol. 282. no. 5389, pp. 718 - 720
DOI: 10.1126/science.282.5389.718
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Reports

Three-Dimensional Structure at the Base of the Mantle Beneath the Central Pacific

Ludovic Bréger, * Barbara Romanowicz

Forward modeling of differential travel times of phases sensitive to lowermost mantle beneath the central Pacific reveals lateral heterogeneity that is higher in amplitude than predicted by tomographic models. A broad zone of low S velocity (-4 percent with respect to standard models), which may correspond to the base of a thermal "plume," narrows and is deflected as it extends to about 1000 kilometers above the core-mantle boundary. To the east of this zone, a localized region of fast S velocity (+5 percent) suggests strong heterogeneity or anisotropy related to the presence of high pressure and temperature assemblages, which may or may not involve core material. Its presence could also explain the observation of precursors to core reflected phases in this region.

Seismological Laboratory, University of California, Berkeley, CA 94720, USA.
*   To whom correspondence should be addressed. E-mail: breger{at}seismo.berkeley.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
From the Cover: The innermost inner core of the earth: Evidence for a change in anisotropic behavior at the radius of about 300 km.
M. Ishii and A. M. Dziewonski (2002)
PNAS 99, 14026-14030
   Abstract »    Full Text »    PDF »
Heavy Nitrogen in Carbonatites of the Kola Peninsula: A Possible Signature of the Deep Mantle.
N. Dauphas and B. Marty (1999)
Science 286, 2488-2490
   Abstract »    Full Text »


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Science. ISSN 0036-8075 (print), 1095-9203 (online)