Gravity observations and 3D structure of the Earth

The determination of Earthʹs gravity field has benefited from various gravity missions that have been launched recently (Champ and Grace) and a new quantitative jump should be made by the Goce mission in a few more years. For the first time, a global high-quality coverage of the Earthʹs gravity is available. In this paper, we review the results that have been obtained to explain Earthʹs gravity on a global scale. We show how we can separate the contributions due to shallow density variations (crust and lithosphere) to those related to the deep mantle. The geoid (or the first degrees of the gravity field) is very simply and well explained by ancient slabs subducting throughout the whole mantle. Such a density distribution is in agreement with tomographic results and qualitatively with what is expected from a convective mantle without a large amount of bottom heating. Although we can produce a simple model that correlates with observations for all degrees and explain most of the geoid, a significant improvement in the fit is possible and will need to take into account the details of the lithospheric structure. To cite this article: Y. Ricard et al., C. R. Geoscience 338 (2006).