The aim of this paper is to analyse the damage on gravity dams through artificial earthquakes from two methods. The first procedure defines the performance and the response curve of concrete gravity dams using a harmonic function which establishes linear displacements. The other procedure to obtain the artificial earthquake defines the power spectral density function consistent with the response spectrum. This artificial accelerogram is necessary to quantify the response curve of concrete gravity dams in the time domain. The seismic activity in Spain is not frequent, therefore it is often difficult to select real accelerograms to perform a complete seismic analysis, which makes artificial accelerograms extremely useful. Finally, combining these two procedures, a damage index is determined for assessing the crack’s magnitude. These both efficient and practical procedures are useful to develop further complicated analysis.