Effects of Operational and Environmental Variability on the Vibration-Based Modal Identification of the Cusco Cathedral

Vibration-based modal identification is widely used to assess the structural condition of historic buildings. However, the reliability of modal identification may be significantly affected by operational and environmental variability. Although environmental effects on modal parameters have been documented in monitored masonry structures, detailed case studies addressing the influence of varying operational excitation levels, especially their impact on mode identifiability in monuments, remain limited. This work presents the preliminary results of an Operational Modal Analysis campaign on the stone-masonry Cusco Cathedral (Peru) during the Corpus Christi festivities in June 2025. A five-day ambient-vibration monitoring campaign was conducted on the main façade while several religious and cultural events took place in front of the Cathedral. The effects of excitation level, temperature, and relative humidity on the identified modal parameters and mode identifiability were assessed. The results highlight the variability and stability of the principal natural modes under changing operational and environmental conditions, and their implications for vibration-based assessment of large heritage churches.