We use the finite-difference method to investigate the effects of irregular structure on ground motions resulting from point sources on the Elysian Park fault. The response computed at several depths beneath the basin suggests that the response is dominated by the initial direct arrivals for sources located interior to the basin. When the receivers are located at one end of the basin, and the seismic sources are located at the opposite edge, the characteristic features on the seismograms are the long durations caused by the trapped energy within the basin. The level of trapped energy decreases as the depth of the source increases. Thus, the fault model becomes important in determining the level of peak ground motions and shaking duration.