Unsound Methods of Probing the Earth’s Core

Résumé: Much of what we know about the structure of the core is inferred from seismic observations of body waves and normal mode oscillations. Inversion of these observations yields estimates for the sound speed and density. Magnetic waves in the core provide another source of information. These waves are detected at the surface as variations in the magnetic field. Analysis of these field variations using methods commonly applied in normal-mode seismology yield estimates for the internal magnetic field and the excitation source for the waves. Comparison of the recovered internal magnetic field with predictions from a numerical geodynamo model are encouraging, and suggests that the poloidal part of the internal field is generated by a large number of convective Taylor columns, arranged in a ring around the core at a radial distance (in cylindrical coordinates) that is slightly greater than the radius predicted in the geodynamo model. The excitation source is confined primarily to the region near the tangent cylinder, and may be due to episodic transfer of mass across the surface of the tangent cylinder. -------------------------------------------------------------------------------- Séminaires généraux de l'Institut de Physique du Globe de Paris --------------------------------------------------------------------------------