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.

Science 15 November 1996:
Vol. 274. no. 5290, pp. 1179 - 1182
DOI: 10.1126/science.274.5290.1179
Prev | Table of Contents | Next

Reports

The Nature of the 660-Kilometer Upper-Mantle Seismic Discontinuity from Precursors to the PP Phase

Charles H. Estabrook * and Rainer Kind dagger

Global Seismic Network data were used to image upper-mantle seismic discontinuities. Stacks of phases that precede the PP phase, thought to be underside reflections from the upper-mantle discontinuities at depths of 410 and 660 kilometers, show that the reflection from 410 kilometers is present, but the reflection from 660 kilometers is not observed. A continuous Lamé's constant lambda  and seismic parameter at the 660-kilometer discontinuity explain the missing underside P reflections and lead to a P-wave velocity jump of only 2 percent, whereas the S-wave velocity and density remain unchanged with respect to previous global models. The model deemphasizes the role of Lamé's constant lambda  with regard to the shear modulus and constrains the mineralogical composition across the discontinuity.

GeoForschungsZentrum Potsdam, Telegrafenberg, D- 14473 Potsdam, Germany.
*   To whom correspondence should be addressed.

dagger    Also at Freie Universität Berlin, Berlin, Germany.

Read the Full Text


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
The Nature of the 660-Kilometer Discontinuity in Earth's Mantle from Global Seismic Observations of PP Precursors.
A. Deuss, S. A. T. Redfern, K. Chambers, and J. H. Woodhouse (2006)
Science 311, 198-201
   Abstract »    Full Text »    PDF »
Seismic Velocity and Density Jumps Across the 410- and 660-Kilometer Discontinuities.
P. M. Shearer and M. P. Flanagan (1999)
Science 285, 1545-1548
   Abstract »    Full Text »


To Advertise     Find Products

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