It is shown that during the growth of InxGa1-xAs on GaAs, the strain-induced lattice distortion oscillates as a function of monolayer completion in both purely 2D and quasi-2D layer-by-layer growth regimes. This is explained by considering that nontetragonal elastic distortion occurs at the free edges of 2D monolayer islands. Numerical relaxation using a simplified model of interatomic forces gives the correct order of magnitude of the strain relaxation by this process.