Gravity anomaly analysis is an essential tool to study the subsurface structure of the lithosphere and mantle. We present the importance for geodynamic studies of the project of World Gravity Map (WGM) undertaken by the International Gravimetric Bureau (IGB) - one of the International Gravity Field Services - under the aegis of the Commission for the Geological Map of the World. The set of 3’×3’-resolution, global digital maps provided by the WGM project will present free-air gravity as well as Bouguer gravity anomalies, both on land and at sea. We plan to release the set of maps during the year 2009, as part of the Year of Planet Earth projects. The digital support will be accompanied by a booklet presenting the contributions and data processing techniques. In geodynamic studies, gravity anomalies are used to image at local and regional scales the mass-density distribution of the Earth’s interior and hence the geological structures from the subsurface, crustal and upper mantle depths. With that aim, the geophysicist usually removes the surface and very deep gravity effects that mask the local or regional sub-surface anomalies which are of interest. The gravity anomaly residuals with respect to a gravity model provide insights into the density anomalies or dynamic forces present in the crust or upper mantle. The objective of the digital WGM project is to compile gravity anomalies on land and at sea, to combine the near-surface observations with satellite-derived gravity models, in order to provide an up-to-date data set which could be used by geophysicists for regional or local studies. A major interest of such a combination of digital maps is to allow the study of continental margins, either passive or active, because it will provide a continuous map on the edge of the continents, an area where very different gravity data sets usually coexist, with on-land local measurements, ship-borne data sets, and sometimes air-borne data sets. The gravity maps will include contributions from major institutions, including estimates of the gravity anomalies from sea surface satellite measurements, as well as contributions from the IGB public-domain data base. We present the gravity compilations in some areas to show the potential interest of these maps for geodynamic studies, and to encourage all contributions to the project, either with gravity data sets or with surface and subsurface information.
BGI/IGB Team: Sylvain Bonvalot, Anne Briais, Michel Sarrailh, Thierry Fayard, Richard Biancale, Sophie Pecquerie, Germinal Gabalda and Nicole Lestieu.