Elastic wave equation
Séminaire de théorie spectrale et géométrie, Volume 25 (2006-2007), pp. 55-69.

The goal of this talk is to describe the Lamé operator which drives the propagation of linear elastic waves. The main motivation for me is the work I have done in collaboration with Michel Campillo’s group from LGIT (Grenoble) on passive imaging in seismology. From this work, several mathematical problems emerged: equipartition of energy between $S-$ and $P-$waves, high frequency description of surface waves in a stratified medium and related inverse spectral problems.

We discuss the following topics:

• What is the definition of the operator and the natural (free) boundary conditions?
• The polarizations of waves ($S-$waves and $P-$waves) and its relation to Hodge decomposition
• The Weyl law and equipartition of energy between $S-$waves and $P-$waves. We formulate here questions in the spirit of Schnirelman’s Theorem about limits of Wigner measures of eigenmodes and of Schubert’s Theorem about the large time equipartition of an evolved Lagrangian state.
• Rayleigh waves for the half-space: we compute in a rather explicit way the spectral decomposition following the work of Ph. Sécher. Of particular interest are the scattering matrix and the density of states.
DOI: 10.5802/tsg.247
Colin de Verdière, Yves 1

1 Université Grenoble 1 Institut Fourier — UMR CNRS-UJF 5582 BP 74 38402-Saint Martin d’Hères cedex (France)
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Colin de Verdière, Yves. Elastic wave equation. Séminaire de théorie spectrale et géométrie, Volume 25 (2006-2007), pp. 55-69. doi : 10.5802/tsg.247. http://www.numdam.org/articles/10.5802/tsg.247/`

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