PSI - Issue 78

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

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To support the continued development of seismic and structural monitoring technologies and to validate the performance of instruments and sensors developed within the “Monitoraggio Sismico Urbano e delle Infrastrutture” group of INGV, a seismic-accelerometric station (BAS01) was installed inside the Basilica of Saint Francis of Assisi on 6 October 202, in collaboration with WISE Robotics. In Figure 2.c and in the table on the left, the hypocentral locations of earthquakes with a local magnitude (M L ) greater than 3.0 recorded since the installation of BAS01 in October 2023 are shown. The map also reports the location (orange circle) of the 25th December 2023 M L 2.0 earthquake (ca. 20 km from BAS01) and the 21st March 2025 M L 3.5 earthquake (ca. 50 km from BAS01). Velocigrams and accelerograms of both the events are presented in Figure 3.

Fig. 3. BAS01 station velocigrams and accelerograms of the 25 December 2023 M L 2.0 earthquake (ca. 20 km from BAS01) and the 21 March 2025 M L 3.5 earthquake (ca. 50 km from BAS01). The maximum Peak Ground Acceleration (PGA) value is measured on the E – W component. The noise at the M L 3.5 horizontal components may depend on mechanical systems that are active mainly during daytime hours. 4. The Structural Health Monitoring Systems The SHM system installed on the bell tower of the Basilica of St. Francis in Assisi is entirely based on ultra-low noise digital QMEMS sensors (Seiko Epson Corporation, Nagano, JP). The locations of the sensors are shown in the tower model presented in Figure 4.a. Six tri-axial M-A552 accelerometers (Figure 4.b), dust- and water-resistant and capable of measuring accelerations up to ±15 g with exceptionally low noise, are distributed at three levels along the tower, up to the bells, despite the absence of rigid floors. The QMEMS sensors have been integrated in the Quakebots SHM system that has been developed by Wise Robotics, as already done with piezoelectric sensors for other applications (Storni et al. 2024). The solution consists of an edge component that manages channel time synchronization, data logging, and data analysis. The edge integrates with the cloud platform, enabling remote system control, sensor configuration and diagnostics, and the configuration of alert thresholds, notifications, and reporting. Seamless data access is guaranteed by the web application and smartphone app, while APIs enable platform integration with third-party software. Built on a distributed computing infrastructure, the platform offers high redundancy and fault tolerance and implements cybersecurity protocols using asymmetric cryptographic keys to guarantee data authenticity, integrity, and non-repudiation. The INGV-OSU seismic station BAS01 (Figure 4.c), located at the base of the Basilica, is also part of the monitoring system and provides measurements of ground-level accelerations. The station includes a data acquisition system comprising a data logger, GNSS-based time synchronization, a 3G/4G modem, and a wideband, three-component velocimeter (ETL3D/5s_H2) that integrates an M-A352 accelerometric sensor (Patanè et al., 2022). The velocimeter with 5s period and 100 Hz high cut-off frequency (noise floor of 10 (nm/s)/√Hz at1 Hz) has been designed ad hoc and integrates the M -A352 QMEMS sensor, which shares the same technical features as the M-A552. This hybrid sensor was specifically designed for monitoring local and regional seismic events, as well as for environmental noise measurements, such as for HVSR analysis and microzonation studies. Both the M-A352 and M-A552 accelerometers incorporate embedded 32-bit digitizers (with 24 effective bits), a sensitivity of 0.06 µg per least significant bit, a frequency bandwidth of up to 400 Hz, and ultra -low power consumption of only 75 mW. Previous studies (e.g. Patanè et al., 2022; Fertitta et al., 2024) show that the self-noise levels of the M-A352 (or M-A552) are much lower than those of other commercial MEMS accelerometers, and the