Seismology and Composition of the Earth

Standard seismological techniques yield the variation of compressional and shear velocity with depth. These velocities are a function of pressure, temperature, composition and molecular structure. In hydrostatic, homogeneous, isotropic and adiabatic regions of the Earth, the density can be estimated from these velocities with the Adams-Williamson equations and the known mass and moment of inertia. Modern methods of analysing the dispersion of surface waves and the periods of free oscillation yield the density in a direct fashion. The two seismic velocities and the density and the variation of these properties with depth completely define the composition of the material of the Earth's interior in the seismic sense of the word.