The present study considers the two-dimensional seismic analysis of a concrete gravity dam along with massed foundation and the reservoir. The coupled system is subjected to spectrally matched mainshock-aftershock sequences, and the response thus obtained has been compared with the case when only the mainshock earthquake ground motion is considered. Response parameters considered are the crest displacement, stress at heel, crack length, dissipated energy and contact displacements. The results suggest that aftershocks lead to an enhancement of these response parameters in a dam that has been damaged due to mainshock but has not yet been repaired. An attempt has also been made to discuss two types of damage indices that are suitable for consideration of the cumulative effect of damage due to aftershocks.