Physics – Geophysics
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.119..617r&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 119, no. 4, p. 617-625
Physics
Geophysics
10
Earth Mantle, Fluid Flow, Geoids, Lithosphere, Two Dimensional Models, Viscosity, Asthenosphere, Boundary Conditions, Finite Element Method, Geodynamics, Geophysics, Topography
Scientific paper
Whereas the oceanic lithosphere is unerlain by a low viscosity layer, the asthenosphere, it appears unlikely that this layer is well developed beneath continental cratons. This difference could represent a lateral viscosity variation of two to three orders of magnitude near the top of the mantle. Previous mantle flow/geoid models have typically neglected this variation. To investigate the impact of such a lateral strength variation on mantle flow and the resulting geoid, we solve for density-driven flow in a 2D box of uniform-viscosity fluid. A dicchotomous lateral viscosity variation near the top of the mantle is modeled by having a no-slip boundary condition over a section of the top of the box, while allowing the remainder of the top to be slip free. For varying fractions of no-slip on the upper boundary, and various values of the wave number, depth and phase of the driving density anomaly, model geoids are found. In contrast to the viscous flow with only a lengthscale of the lateral viscosity structure, with amplitudes as large as 20-40% in some cases. Thus, coupling can produce a significant signal in the geoid at a wavelegth longer than that of the driving load. This result suggests that the accuracy of models of the geoid that assume a solely radial viscosity structure may be limited to the 60-80% level found in recent studies. We speculate that some of the Earth's low-order geoid is due to flow coupling resulting from the degeree two to five components of the lateral ocean-continent structure.
Phipps Morgan Jason
Ravine Michael A.
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