This copy is for your personal, non-commercial use only.
If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission torepublish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this information is current as of May 23, 2010 ): Updated information and services, including high-resolution figures, can be found in the online version of this article at:http://www.sciencemag.org/cgi/content/full/294/5541/357 Supporting Online Material can be found at: http://www.sciencemag.org/cgi/content/full/294/5541/357/DC1 This article cites 13 articles, 1 of which can be accessed for free: http://www.sciencemag.org/cgi/content/full/294/5541/357#otherarticles This article has been cited by 35 article(s) on the ISI Web of Science. This article has been cited by 2 articles hosted by HighWirePress; see: http://www.sciencemag.org/cgi/content/full/294/5541/357#otherarticles This article appears in the following subject collections: Paleontology http://www.sciencemag.org/cgi/collection/paleo
Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW,Washington, DC 20005. Copyright 2001 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS.
Downloaded from www.sciencemag.org on May 23, 2010
13. P. R. Cummins, B. L. N. Kennet, J. R. Bowman, M. G. Bostock, Bull. Seismol. Soc. Am. 82, 323 (1992). 14. H. M. Benz, J. E. Vidale, Nature 365, 147 (1993). 15. Weincluded 1530 events with a depth from 0 to 75 7.0, and from km, a magnitude of 6.0 Mw stations in the epicentral distance range 100° 160° for the period 1 January 1980 to 29 March 1998. The SS phases in the individual traces are hand-picked, and the data is deconvolved for receiver effects and bandpass-ﬁltered between 15 and 75 s. 16. The size of the caps corresponds to the Fresnel zone of the SSrays. Neighboring caps overlap partly to ensure smoothing. 17. B. Efron, R. Tibshirani, Science 253, 390 (1991). The data set was also divided into two subsets with epicentral distances from 100° to 130° and 130° to 160°; splitting was still present in stacks of the subsets. 18. Supplementary material is available at www. sciencemag.org/cgi/content/full/294/5541/354/DC1 19. The stacks arecross-correlated with the SS pulse; splitting is determined by two cross-correlation maxima (instead of one) in the depth range of 480 to 600 km. 20. We ﬁnd single reﬂections from 520 km for stacks corresponding to different regional types (shields, tectonically active regions, stable continents, and oceans). The stacks exhibit somewhat different amplitudes and, in particular, the shield stack shows asmaller amplitude, conﬁrming an earlier study (6). N. A. Simmons, H. Gurrola, Nature 405, 559 (2000). D. Canil, Phys. Earth Planet. Inter. 86, 25 (1994). S. Koito, M. Akaogi, O. Kubuta, T. Suzuki, Phys. Earth Planet. Inter. 120, 1 (2000). D. J. Weidner, Y. Wang, in Earth’s Deep Interior: Mineral Physics and Tomography from the Atomic to the Global Scale (Geophysical Monograph 117, AmericanGeophysical Union, Washington, DC, 2000), pp. 215–235. J. Ritsema, H. J. van Heijst, J. H. Woodhouse, Science 286, 1925 (1999). Y. Fei, C. Bertka, in Mantle Petrology: Field Observations and High-Pressure Experimentation, Special Publication in honor of Francis R. Boyd, Geochem. Soc. Spec. Pub. (Geochemical Society, Washington University, St. Louis, MO, 1999), vol. 6, pp. 189 –207. T. Inoue, D. J....