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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 99, NO. B10,
PAGES 19,843–19,852,
1994
Subducted slabs and the geoid 1. Numerical experiments with temperature-dependent viscosity
Scott D. King
Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana
Bradford H. Hager
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge
Abstract
One of the most powerful constraints on mantle viscosity comes from the correlation of the long-wavelength (degree 4–9) geoid
with that predicted by a density model for subducted slabs. The effect of lateral variations of viscosity should be most pronounced
at subduction zones, due to the strong effect of temperature on viscosity. An idealized slab model with temperature-dependent
viscosity is considered, with various lateral and vertical viscosity structures, using a two-dimensional finite element formulation.
The viscosity parameterization affects the amplitude of the long-wavelength geoid anomaly but not the sign of the correlation
between the geoid and density anomalies. Depth-dependent viscosity models with a high-viscosity lithospheric layer do not
completely match the temperature-dependent (laterally varying) results, suggesting that the rheology of the slab does have
an effect on the long-wavelength surface topography and geoid; however, this affect is minor, suggesting that the radial models
of mantle viscosity inferred from surface observables are correct to first order. In contrast, the short-wavelength features
are dramatically affected by the rheology of the region surrounding the downwelling. Further study of the shorter-wavelength
geoid over subduction zones may provide better insight into subduction zone processes.
Received 1
July
1993;
accepted 13
June
1994.
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Citation: King, S. D., and B. H. Hager
(1994),
Subducted slabs and the geoid 1. Numerical experiments with temperature-dependent viscosity,
J. Geophys. Res.,
99(B10),
19,843–19,852.
Copyright 1994 by the American Geophysical Union.
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