HR: 11:20h
AN: G32A-05    [Abstracts]
TI: The Effect of Mantle Heterogeneity on Tidal Gravity and Surface Deformations
AU: * Metivier, L
EM: metivier@jhu.edu
AF: Johns Hopkins University, Department of Earth and Planetary Sciences, 3400 North Charles Street, Baltimore, MD 21216, United States
AU: Conrad, C P
EM: conrad@jhu.edu
AF: Johns Hopkins University, Department of Earth and Planetary Sciences, 3400 North Charles Street, Baltimore, MD 21216, United States
AB: Precise knowledge of Earth tides is crucial for correcting the signal from satellite gravity surveys or superconducting gravimeters with nanoGal precision. Some local observations show unexplained perturbations to the tidal gravity signal. This noise is generally considered to result from unmodeled loading induced by oceanic tides, but it is possible that an unmodeled component of Earth's body tides contributes to this noise. In fact, the strain and gravity responses of the Earth to body tides are generally computed assuming a radially (or elliptically) stratified Earth. However, seismic tomography surveys and fluid dynamic studies show that thermal convection in Earth's mantle produces significant heterogeneity. Superplumes beneath the Pacific and South Africa superswells, and descending slabs that ring the Pacific are examples of this internal heterogeneity. We have determined body tides for a non-radially symmetric earth model using a spectral element method. The structure of the laterally-heterogeneous mantle interior has been inferred from a tomographic model. We couple this heterogeneity to a viscous convection model to compute dynamic topography on surface and CMB, and verify the complete Earth model using geoid observations. We investigated semi-diurnal, diurnal and a few longer periods wave tides. We show that laterally-varying mantle structure induces perturbations in surface tidal response of the solid Earth of about 1 per mil. Using a tidal catalogue, we show that the maximum perturbation of radial tidal and geoid displacements are about 0.25 mm and about 0.1 mm, respectively, and the maximum perturbation of tidal gravity variation is about 120 nanoGal. This gravity perturbation is 100 times larger than the present precision of superconducting gravimeters and is at the level of the observed tidal noise. However, the amplitudes of tidal perturbations depend strongly on location, and are particularly high above large dense slabs (such as those near South America, Indonesia, and the Marianas) or over hotspots of Hawaii or Iceland, and over the East African Rift. Some of these regions exhibit unusually large tidal noise, suggesting that perturbations to the body tides might be an important source of this noise.
DE: 0545 Modeling (4255)
DE: 1211 Non-tectonic deformation
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1217 Time variable gravity (7223, 7230)
DE: 7208 Mantle (1212, 1213, 8124)
SC: Geodesy [G]
MN: 2007 Fall Meeting