PSI - Issue 78

Daniele Storni et al. / Procedia Structural Integrity 78 (2026) 237–244

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Fig. 7. Frequency tracking during the observation period between 2023-09-01 and 2025-02-20

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Fig. 8 Influence of a) temperature, b) humidity and c) wind on the frequencies

6. Conclusions The Basilica of St. Francis in Assisi, a monument of extraordinary historical, artistic, and spiritual value, is located in one of the most seismically active areas of central Italy. Following the significant damage, it sustained during the 1997 earthquake, the protection and preservation of its structural integrity have become a critical concern. In response, a long-term SHM system was implemented between 2022 and 2023, focusing on both the nave vaults and the bell tower — a key architectural and symbolic component of the complex. The INGV OSU seismic station (BAS01) placed at the base of the monumental complex, which features a wide-band velocimeter and an M-A352 accelerometer, demonstrates a high signal-to-noise ratio in the accelerometric signals that enables clear identification of seismic phases for earthquakes with M L around 2.0 at distances of approximately 20 – 25 km, and M L of about 3.0 at distances up to ca. 50 km. This performance highlights the station’s suitability for testing early warning system ( EEW) capabilities across this range of distances. With the Wise Robotics platform, the system allows for ongoing observation of the Basilica’s movements and quick identification of any structural issues. The bell tower's dynamic patterns, determined through OMA, were successfully tracked for two years, showing a steady behavior mainly affected by changes in temperature. An extensive frequency-weather parameters correlation has been performed and a non uniform dependency of the identified modes on weather parameters has been obtained. Notably, temperature affects all modes, with the strongest effect observed on the fifth mode at +7.47 mHz/°C. Humidity has a less pronounced effect, primarily impacting the fifth mode as well with a variation of -1.19 mHz/%RH. High sensitivity of sensors enabled the system to capture responses even from distant, low-magnitude seismic events. Analyzing how the tower