Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Site Tools

  • AAAS
  • Subscribe
  • Feedback

Site Search

Search Advanced

Science 13 March 1998:
Vol. 279. no. 5357, pp. 1701 - 1703
DOI: 10.1126/science.279.5357.1701
Prev | Table of Contents | Next

Reports

Ultra-Low Velocity Zones Near the Core-Mantle Boundary from Broadband PKP Precursors

Lianxing Wen, * Donald V. Helmberger

Short- and long-period precursors of the PKP phase were used to study an ultra-low velocity zone (ULVZ) near the core-mantle boundary beneath the Western Pacific. Synthetic seismograms were computed from a hybrid method, which handles seismic wave propagation through two-dimensional complex structures. Long-period precursors were explained by Gaussian-shaped ULVZs of 60 to 80 kilometers height with P velocity drops of at least 7 percent over 100 to 300 kilometers. Short-period precursors suggest the presence of smaller scale anomalies accompanying these larger Gaussian-shaped structures. These fine structures may be areas of partial melt caused by vigorous small-scale convection or the instability of a thermal boundary layer at the mantle's base, or both.

Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA.
*   To whom correspondence should be addressed. E-mail: wen{at}gps.caltech.edu

Read the Full Text


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Implications of lower-mantle structural heterogeneity for the existence and nature of whole-mantle plumes.
E. J. Garnero, T. Lay, and A. McNamara (2007)
Geological Society of America Special Papers 430, 79-101
   Abstract »    Full Text »    PDF »
The inner inner core of Earth.
D. L. Anderson (2002)
PNAS 99, 13966-13968
   Full Text »    PDF »
Origins of High-Frequency Scattered Waves near PKKP from Large Aperture Seismic Array Data.
(2002)
Bulletin of the Seismological Society of America 92, 751-760
Distribution of Fine-Scale Mantle Heterogeneity from Observations of Pdiff Coda.
(2001)
Bulletin of the Seismological Society of America 91, 1875-1881
Contrasting behavior of noble-metal elements during magmatic differentiation in basalts from the Cook Islands, Polynesia.
Y. Tatsumi, K. Oguri, G. Shimoda, T. Kogiso, and H. G. Barsczus (2000)
Geology 28, 131-134
   Abstract »    Full Text »    PDF »
Lower Mantle Lateral Heterogeneity Beneath the Caribbean Sea.
I. M. Tibuleac and E. Herrin (1999)
Science 285, 1711-1715
   Abstract »    Full Text »
A Diamond Trilogy: Superplumes, Supercontinents, and Supernovae.
S. E. Haggerty (1999)
Science 285, 851-860
   Abstract »    Full Text »
Three-Dimensional Structure at the Base of the Mantle Beneath the Central Pacific.
L. Bréger and B. Romanowicz (1998)
Science 282, 718-720
   Abstract »    Full Text »
Solidus of Earth's Deep Mantle.
A. Zerr, A. Diegeler, and R. Boehler (1998)
Science 281, 243-246
   Abstract »    Full Text »


To Advertise     Find Products

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