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The Nature of the 660-Kilometer Upper-Mantle Seismic Discontinuity from Precursors to the PP Phase
Charles H. Estabrook and Rainer Kind
New Series, Vol. 274, No. 5290 (Nov. 15, 1996), pp. 1179-1182
Published by: American Association for the Advancement of Science
Stable URL: http://www.jstor.org/stable/2891589
Page Count: 4
You can always find the topics here!Topics: Seismographs, Velocity, Wave reflection, Earth, Reflectance, P waves, Seismology, Shear modulus, Olivine, Signal reflection
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Global Seismic 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 λ 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 λ with regard to the shear modulus and constrains the mineralogical composition across the discontinuity.
Science © 1996 American Association for the Advancement of Science