This paper presents an analysis of the effect of flare-induced shock waves on the intensity of relativistic cosmic rays at 1 AU. We find that the intensity of cosmic ray protons falls abruptly as the shock wae passes the earth and recovers as the compression region moves into the outer heliosphere. The intensity versus time profile we obtain is consistent with observed flare-induced Forbush decreases. The principal mechanism is found to be simply prolonged containment of the cosmic ray particles in the region between the flare shock wave and the sun. This leads to additional adiabatic cooling of the particles and a corresponding decrease in particle intensity. Acceleration mechanisms at the shocks are found to play little role at relativistic energies. We investigate the dependence of both the maximum intensity decrease and recovery time on such parameters as particle diffusion coefficient, particle rigidity, and flare geometry. It is found that flares located to the east of the earth-sun line produce effects than those located to the west. The magnitude of the intensity reduction decreases as a function of increasing diffusion coefficient and increasing particle rigidity. Throughout most of our analysis we assume the flare compression region to have a longitudinal extent of 180¿, but as an extreme case we investigate the effect of a completely spherical blast wave. This, as expected, has a substantilly increased effect on both the magnitude of the decrease and, more significantly, on the recovery profile.