First, the present paper is concerned with the extension to linearized elastodynamics of the optimal results known in statics for the mortar method. It also analyzes and tests a new couple of displacements/Lagrange multipliers for the method, as proposed independently by Ben Belgacem [F. Ben Belgacem, A stabilized domain decomposition method with non-matching grids for the Stokes problem in three dimensions, SIAM J. Numer. Anal. 42 (2) (2004) 667–685] and the authors [P. Hauret, Méthodes numériques pour la dynamique des structures non-linéaires incompressibles à deux échelles (Numerical methods for the dynamic analysis of two-scale incompressible nonlinear structures), Ph.D. thesis, Ecole Polytechnique, 2004]. Finally, questions of practical implementation in the presence of curved interfaces are addressed and validated from the numerical point of view.