This series of five lectures focused on seismic imaging methods, as developed over the last forty years or so to study the global deep structure of the Earth's mantle. The principle is similar to that of medical imaging : how can we obtain an image of the internal structure of a body by placing wave sources and sensors on its surface ?
To the first order and to a very good approximation, the Earth is made up of concentric spherical layers, so the elastic structure of its solid mantle (from the surface to a depth of 2 900 km) can be described using a single parameter - depth. However, there are geographical variations in temperature and composition due to the fact that our planet is " dynamic ". In particular, to release the internal heat stored in the core and mantle, the mantle is animated by convection movements - which, although very slow (on the order of 10 km/Ma), are manifested at the surface by the movements of tectonic plates. The seismic waves generated by a strong earthquake propagate through the Earth's interior, at speeds that vary during propagation and depend on the elastic properties of the materials encountered along the way, which in turn depend on the temperature and composition of these rocks. Thanks to seismic tomography, combined with information from other disciplines (materials physics, geochemistry, geodynamic modelling), we have an increasingly precise idea of the morphology of these mantle convection currents, enabling us to better understand surface observations and their variation over time : distribution of continents, earthquakes and volcanoes, submerged mountain ranges (or ridges) on the ocean floor, etc., as well as the evolution of the Earth's crust, as well as the evolution of the Earth since its formation some 4.6 billion years ago.