DYNAMIC SURFACE-TOPOGRAPHY - A NEW INTERPRETATION BASED UPON MANTLE FLOW MODELS DERIVED FROM SEISMIC TOMOGRAPHY

The very long wavelength (i.e. in the degree range l = 1-8) dynamic topography at the Earth's surface, estimated by isostatic reduction of the observed topography, is shown to be in good agreement with the topography predicted by a model of viscous flow in mantle. This flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large-scale seismic shear velocity heterogeneity in the mantle. Our estimate (and prediction) of the long wavelength dynamic surface topography reveals significant depressions (almost-equal-to 2-3 km) of the continental shields relative to their hydrostatic reference positions.