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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 of the Royal Society of London. Series A: Mathematical and physical sciences, 328 (1599). pp. 309-327. ISSN 0080-4614. doi:10.1098/rsta.1989.0038.

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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. 10²⁰ 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.

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Hager, B. H.0000-0002-5643-1374
Additional Information:© 1989 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.
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Caltech Division of Geological and Planetary Sciences4625
Issue or Number:1599
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Official Citation:Hager B. H. and 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 328:309–327
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105648
Deposited By: George Porter
Deposited On:30 Sep 2020 14:26
Last Modified:16 Nov 2021 18:45

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