The Mohorovičić discontinuity or Moho (from the name of the Croatian seismologist who discovered it in 1909) is the boundary between the Earth crust and mantle. It is a sharp surface separating rocks with different properties at a depth that ranges from 25 km to more than 90 km beneath continents and from 5 km to 15 km beneath the sea floor. A good knowledge of the Moho discontinuity is the base for studies concerning the dynamic of the solid Earth: it will permit to better understand heterogeneities of the lithosphere and represents a major input for the geodynamic modeling (e.g. for the evaluation of seismic hazard and for the reliable retrieval of earthquake source mechanisms).

Since the upper part of the mantle is denser than the crust, the Moho depth can be inferred from gravity data. The main aim of the GEMMA project is to map the crust-mantle discontinuity in key regions of the world by means of observations coming from the innovative ESA satellite mission GOCE. This will allow, for the first time, estimating a Moho model without any need for geophysical interpretation (avoiding the uncertainties connected with this operation). Moreover, since the main input are gravimetric data collected by the satellite mission GOCE it will be possible to estimate the Moho almost worldwide (also where gravity or seismic observations are not available for political or economical reasons). Furthermore, by combining GOCE gravimetric data with altimetry data from ESA CryoSat 2, the inversion algorithm will allow also to improve knowledge on the Cryosphere. In particular, it will be possible to improve the knowledge on the mass distribution beneath ice surface. Finally, the integration of space-geodetic observations and geophysical information will improve the ability to understand, monitor, predict and control geophysical processes.