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

Abstract

Growing 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.

BibTeX
@article{id2162,
  author = {Colli, Lorenzo and Ghelichkhan, Siavash and Bunge, Hans-Peter},
  doi = {10.1002/2016GL067929},
  journal = {Geophysical Research Letters},
  language = {en},
  number = {6},
  pages = {2510{\textendash}2516},
  title = {On the ratio of dynamic topography and gravity anomalies in a dynamic Earth},
  volume = {43},
  year = {2016},
}
EndNote
%O Journal Article
%A Colli, Lorenzo
%A Ghelichkhan, Siavash
%A Bunge, Hans-Peter
%R 10.1002/2016GL067929
%J Geophysical Research Letters
%G en
%N 6
%P 2510–2516
%T On the ratio of dynamic topography and gravity anomalies in a dynamic Earth
%V 43
%D 2016