Geoid Height and Swell-Push Force in the Lithospheres of Venus and the Earth

Details Geoid Height and Swell-Push Force in the Lithospheres of Venus and the Earth Geoid Height and Swell-Push Force in the Lithospheres of Venus and the Earth

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.u62a..03s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #U62A-03

Physics

1213 Earth'S Interior: Dynamics (8115, 8120)

Scientific paper

The thermal boundary layer model for the cooling oceanic lithosphere [Turcotte and Oxburgh, J. Fluid. Mech. V. 28, 1967] provides a remarkably accurate description of seafloor depth, heat flow, lithospheric strength, and swell-push force. However the global stress field of the Earth is still poorly determined because the slab-pull force dominates. Don Turcotte [J. Geophys. Res., v. 98, 1993] proposed that lithospheric cooling is the dominant convective mechanism on Venus and therefore the swell-push force dominates the stress field of the Venusian lithosphere. Is this simple model consistent with observations of faults and fractures on Venus? I use new high-resolution geoid and topography models for Venus and the Earth to construct planetary stress and compare these with observations of small-scale surface structure. Venus has a very high correlation between geoid height and topography at all wavelengths so it is reasonable to assume that the swell-push force dominates. This swell-push body force is applied to a uniform thickness elastic shell over an inviscid sphere, to calculate the present-day global strain field [Sandwell et al., ICARUS, v. 129, 1997]; areas of positive geoid height are in a state of extension while areas of negative geoid height are in a state of compression. This model strain pattern is highly correlated with the global strain patterns inferred from Magellan-derived maps of wrinkle ridges and rift zones. Much of the observed deformation matches the present-day model strain orientations suggesting that most of the rifts on Venus and many of the wrinkle ridges formed in a stress field similar to the present one. In contrast to Venus, the correlation between geoid height and topography on the Earth is poor for spherical harmonic degrees less than 9. Moreover, stress in the Earth's lithosphere is the sum of three forces, slab pull, swell push and asthenospheric drag. These complications make it difficult to uniquely establish the global stress field for the Earth?s lithosphere. To address this problem, Earth's geoid is decomposed into a "lithosphere" contribution and a "deep mantle" contribution by making plausible assumptions about the compensation mechanisms of the continents and the seafloor spreading ridges (i.e., ridges are weak). This ?lithospheric? contribution is used to construct a partial global stress model. Results show good agreement with the style of faulting in mountainous areas of the continents but poor agreement with inferred stress patterns in the ocean basins suggesting slab pull is the dominant mechanism in the oceans.

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