Following along the line of the theory proposed initially at CFA-2010, the present contribution presents the recent progress achieved in this trend of research. In particular, for some exemplary modes of propagation, it is shown that quasi-particles of definite “mass” can be associated with these modes via an application of the celebrated Noether’s theorem of variational field theory (or its generalization in presence of dissipation). New results include accounting for (i) the elastic nonlinearity of the substrate, (ii) its viscosity, (iii) the presence of a thin glued active film on top of the surface. The motion of the exhibited quasi-particles may be inertial, or not (in the presence of friction related to viscosity). It is reminded that the main tool here is the exploitation of the canonical conservation laws of wave momentum and energy integrated over a volume element representative of the wave mode. The problem of transmission-reflection at an interface between two elastic media is considered as an example showing the alternate wavelike and particle-like pictures of the solution. References: Proc. Roy. Soc. London, A467, 495-507, 2011; Int. J. Eng. Sci., 48, 1462-1469, 2010; ibid, 50, 10-21, 2012; Int. J. Non-linear Mech., 47, 67-71, 2012.