Earthquake engineering issues with bradyseism at Campi Flegrei: end 2024 - late 2025 update

Between January and late September 2025, thousands of earthquakes were recorded at Campi Flegrei (southern Italy). These events are attributed to the ground uplift (currently a few centimetres per month) of the area due to volcanic activity, named bradyseism. Among the earthquakes of the sequence, which has lasted for some years so far, the largest estimated duration magnitude (Md) reached 4.6. Complementing recent work by the authors, this study provides an updated analysis of the recent earthquakes from a structural engineering perspective. Focusing on earthquakes with Md ≥ 2.5 that occurred between March 2022 and September 2025, the study analyses the response spectra for the Md ≥ 4.4 events, maps the estimated shaking for the Md = 4.6 earthquake of March 2025, and maps the envelopes of estimated shaking from all events considered. Finally, the structural response of equivalent single-degree-of-freedom (ESDoF) systems representative of code-conforming unreinforced masonry (URM) and reinforced concrete (RC) buildings, subjected to the whole sequence of Md ≥ 2.5 earthquakes, are discussed. Results show that the largest shaking of the sequence was recorded during the
Md = 4.6 event of March 2025, with peak ground accelerations greater than 0.7 g recorded at three stations within 1.6 km from the epicentre of the event. Nonlinear dynamic analysis of the ESDoF systems confirms that the impact of the sequence is negligible for the code-conforming RC structures, while the considered URM structure engages plastic excursions during the March Md = 4.6 event, even in western Naples, and also during other events (mostly occurring in 2025) with Md between 3 and 4, and epicentral distance of about 1.5 km at most.