A method is presented for modeling earthquake strong ground motion, which uses the aftershocks associated with a large earthquake as Green's functions. A major earthquake, with a large rupture surface, is modeled by a collection of point sources distributed over the fault plane. The response of each point source is approximated by the ground motion of the closest associated aftershock. By using the aftershock responses, the effects of the true earth structure are included in the modeling process. This method is used to model the El Centro displacement record for the 1940 Imperial Valley earthquake.