Historical buildings are of foremost importance due to their unique and irreplaceable value. However, their ageing structure and materials make them particularly vulnerable to structural damage. This may result in catastrophic failure under strong motions, which are unfortunately not uncommon in seismic areas such as most of Italy. This numerical study discusses the application of Discrete Wavelet Transform (DWT) and Wavelet Levels (WLs) to the seismic response of such historical structures. The simulated data are obtained from a calibrated Finite Element (FE) model of the Santa Maria and San Giovenale Cathedral bell tower in Fossano (Northern Italy). This structure suffered major structural damage during an earthquake in 1887; it then underwent several reinforcement interventions, the last one being in 2012. It is also currently scheduled for further reinforcement works in the near future. The FE analyses apply a set of realistic earthquake inputs, defined in accordance with the seismic hazard zone of Fossano, to the structure with and without damage (modelled as a stiffness reduction in the façades, considering several possible crack patterns). The results show the potential for WL-based retrospective analysis after seismic events on recorded signals.