Assessment of the dynamic response of Croatian cultural heritage buildings to microseismic noise measurements

Purpose The 2020 Zagreb and Petrinja earthquakes caused damage to cultural heritage buildings in Croatia, motivating an investigation of their seismic response using non-invasive methods. This study focuses on two monuments: Trakošćan Castle and the Cathedral of St James in Šibenik. Design/methodology/approach Non-invasive ambient noise measurements are diagnostic tool for the preliminary assessment of post-earthquake effects. Ambient vibration measurements were conducted at Trakošćan Castle after the 2020 earthquakes and compared with pre-earthquake data to identify changes in dynamic properties. For the Cathedral of St James, pre-earthquake ambient vibration measurements of the structure were integrated with a microzonation study of predominant ground frequencies in its surroundings to assess potential soil-structure interaction effects. Findings For Trakošćan Castle, the comparison of pre- and post-earthquake data indicates a decrease in the natural frequencies of the tower and the second floor, suggesting an overall reduction in stiffness. The relationship between the frequencies of the Castle’s structures and the site frequencies may indicate possible soil-structure resonance and topographic amplification effects inferred from peak proximity. In the case of the Cathedral of St James, the combined analysis of free-field and in-structure measurements highlights critical structural components, particularly the right-side wall, the left gallery and the dome. Originality/value The study demonstrates the applicability of ambient vibration techniques and site-frequency characterization for rapid post-earthquake diagnostics of complex heritage structures. The results provide a basis for future research on the dynamic response and seismic monitoring of these monuments, with the aim of defining strengthening and preservation strategies for vulnerable cultural heritage buildings.