A mechanism of strain relief of pseudomorphic Si1-xGex/Si(100) heterostructures by Si+ ion implantation and annealing is proposed and analytically modeled. The degree of strain relaxation is presented as a function of Ge content and implantation and annealing parameters. Rutherford backscattering spectrometry/channeling, Raman spectroscopy, and transmission electron microscopy are employed to quantify the efficiency of the relaxation process and to examine the quality of the samples, respectively. The mechanism and the conditions for strain relaxation are discussed in terms of dislocation loop formation in the implanted range with emphasis on loop formation in the compressively strained SiGe layer. The detrimental effect of local amorphization of the SiGe layer on its relaxation and on strain transfer to the Si-cap layer is also addressed.