Comments on the Paper 'On Variational Principles and Matrix Methods in Elastodynamics' by B. L. N. Kennett

Summary Kennett has shown how the equations of elastodynamics may be derived from a variational principle (see also Lanczos, Germain) and attempted to extend this method to the ‘Minor Matrix’ system (Gilbert & Backus). Unfortunately such a direct extension is impossible as will be shown below. However in the case of a medium composed of a series of homogeneous layers, it is possible to construct a stationary expression by a simple transformation. Our discussion will be limited to P-SV or Rayleigh waves in such a medium. References to the equations of Kennett will be denoted, e. g. (K- 4. 1).