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Published January 21, 1966 | public
Journal Article

Earth's Viscosity


Seismic methods are now being used to determine not only Earth's elastic properties, but also by how much it departs from a perfectly elastic body. The seismic anelasticity (Q) varies by several orders of magnitude throughout the mantle, the main feature being an extremely dissipative zone in the upper mantle above 400 kilometers. Recent determinations of viscosity by McConnell show a similar trend. The two sets of data indicate that the ratio of viscosity to Q is roughly a constant, at least in the upper mantle of Earth. On the assumption that this relation is valid for the rest of Earth, viscosities are estimated in regions that are inaccessible for direct measurement. The implied presence of a low-viscosity zone in the upper mantle, overlying a more viscous, less deformable, lower mantle, reconciles viscosities calculated from the shape of Earth and from postglacial uplift. The mismatch of the deformational characteristics at various levels in Earth, coupled with the changing rate of rotation, may be pertinent to the rate of release of seismic energy as a function of depth.

Additional Information

© 1966 American Association for the Advancement of Science. Received 13 September 1965. I thank F. Press. D G. Harkrider, and B. Kamb for helpful discussions during preparation of this report. Research assisted by the Advanced Research Projects Agency and monitored by the U.S. Air Force Office of Scientific Research under contract AF-49(638)-1337, and by the Sloan Foundation. Contribution 1358, Division of Geological Sciences, California Institute of Technology.

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October 26, 2023