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Long-wavelength variations in Earth's geoid: physical models and dynamical implications

Hager, B. H. and Richards, M. A. (1989) Long-wavelength variations in Earth's geoid: physical models and dynamical implications. Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, 328 (1599). pp. 309-327. ISSN 1364-503X . http://resolver.caltech.edu/CaltechAUTHORS:20141113-131525233

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Abstract

The seismic velocity anomalies resolved by seismic tomography are associated with variations in density that lead to convective flow and to dynamically maintained topography at the Earth's surface, the core--mantle boundary (CMB), and any interior chemical boundaries that might exist. The dynamic topography resulting from a given density field is very sensitive to viscosity structure and to chemical stratification. The mass anomalies resulting from dynamic topography have a major effect on the geoid, which places strong constraints on mantle structure. Almost 90% of the observed geoid can be explained by density anomalies inferred from tomography and a model of subducted slabs, along with the resulting dynamic topography predicted for an Earth model with a low-viscosity asthenosphere (ca. 10^(20) Pa s) overlying a moderate viscosity (ca. 10^(22.5) Pa s) lower mantle. This viscosity stratification would lead to rapid mixing in the asthenosphere, with little mixing in the lower mantle. Chemically stratified models can also explain the geoid, but they predict hundreds of kilometres of dynamic topography at the 670 km discontinuity, a prediction currently unsupported by observation. A low-viscosity or chemically distinct D" layer tends to decouple CMB topography from convective circulation in the overlying mantle. Dynamic topography at the surface should result in long-term changes in eustatic sea level.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1098/rsta.1989.0038 DOIArticle
http://rsta.royalsocietypublishing.org/content/328/1599/309.abstractPublisherArticle
Additional Information:© 1989 The Royal Society. Close interaction with R. W. Clayton, R. P. Comer, and R. J. O'Connell was essential to this research. Critical reviews by D. L. Anderson, U. R. Christensen, W. Kiefer, and B. Parsons improved the manuscript substantially. This work was supported by NASA grants NAG5-315 and NAG5-842. This is contribution number 4625, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
Funders:
Funding AgencyGrant Number
NASANAG5-315
NASANAG5-842
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Caltech Division of Geological and Planetary Sciences4625
Record Number:CaltechAUTHORS:20141113-131525233
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141113-131525233
Official Citation:Hager, B. H., & Richards, M. A. (1989). Long-Wavelength Variations in Earth's Geoid: Physical Models and Dynamical Implications. Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, 328(1599), 309-327. doi: 10.1098/rsta.1989.0038
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51717
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:14 Nov 2014 16:58
Last Modified:20 Nov 2014 23:42

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