On the ratio of dynamic topography and gravity anomalies in a dynamic Earth

Abstract

AbstractGrowing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free‐air gravity anomalies (<30 mGal) associated with Earth's long‐wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well‐established formalism of global, self‐gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half‐space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal.