Elastic seismic wave equation and P/S wave speed ratio (geophysics)

Geophysics application of L0 wave-equation-PDE and Sturm–Liouville theory. Infinitesimal elastic displacements u(x, t) in an isotropic medium obey the Navier (Lamé) equation ρ∂²u/∂t² = (λ+2μ)∇(∇·u) − μ∇×(∇×u), which Helmholtz-decomposes…