The modal basis of elastic open waveguides contains two continua of radiation modes and a discrete set of trapped modes. A third set also exists: the leaky modes. However, they do not belong to the modal basis as they spatially grow to infinity. Herein, the excitation of elastic open waveguides is investigated. For numerical pur- pose, the infinite transverse direction is model- led with a truncated perfectly matched layer (PML). Indeed, the PML offers a natural way to reveal the contribution of leaky modes. The PML gives access to the improper Riemann sheets by redefining the branch cuts, yielding two ro- tated continua of radiation modes (PML modes). The cases of an infinite medium and an open waveguide are considered. It is shown that all sets are necessary for achieving convergence of the modal expansion.