Anisotropy of the 1ʳᵉ seed part : discovery, radial structure, hemispheric variations

We have described the different modes of seismic anisotropy and their physical cause, and given some elements of elasticity theory. We also introduced the notion of splitting eigenmodes in the presence of lateral heterogeneities and anisotropy. We described the observations of anomalous splitting of core-sensitive eigenmodes and faster PKIKP volume wave propagation times on polar paths than on equatorial paths, which led to the hypothesis that the seed is anisotropic and the corresponding anisotropic models, and their possible physical causes (convection in the seed, anisotropic growth, iron crystal alignments at the time of crystallization in the presence of the magnetic field etc.). Finally, we have begun to address seismic observations involving a complex seed model.