How could cumulative damage affect the macroseismic assessment?

When strong earthquakes occur, buildings are usually affected by multiple, consecutive seismic shakings causing a progression of the damage. This paper presents a comprehensive discussion on how the cumulative damage caused by multiple shocks could influence the assignment of macroseismic intensity. The potential consequences in case of single or multiple shocks are investigated through a large set of simulations, applying a simplified non-linear structural model on a stock of masonry buildings taken from real cases. The results allow an estimation of the changes in vulnerability, with reference to the European Macroseismic Scale classification, for the buildings that suffered a specific damage in a prior shock. Simulations reckon a significant difference in the macroseismic intensity assignments, especially when the same damage is associated to single or multiple seismic shocks. We highlight the potential bias due to the cumulative damage on the correlation between macroseismic intensity and ground motion parameters, and we formulate a proposal for testing on the field, in the case of future earthquakes, what has been here investigated through a simplified simulation.