  In this paper we analyze a posteriori error estimates for a mixed formulation
of the linear elasticity eigenvalue problem. A posteriori estimators for the
nearly and perfectly compressible elasticity spectral problems are proposed.
With a post-process argument, we are able to prove reliability and efficiency
for the proposed estimators. The numerical method is based in Raviart-Thomas
elements to approximate the pseudostress and piecewise polynomials for the
displacement. We illustrate our results with numerical tests.
