Ground Motion, Estimated Shaking, and Structural Response at Campi Flegrei During Bradyseism

Campi Flegrei, a densely populated volcanic area bordering the city of Naples (Italy), is currently undergoing volcanic unrest accompanied by seismic activity. Between August 2023 and December 2024, 32 events with duration magnitude (Formula presented.) equal to or larger than (Formula presented.) were recorded, with the largest one (Formula presented.). More than 1000 three-component accelerometric waveforms from these events were collected in a database made available as supplemental material to this paper, for earthquake engineering analyses. Using the database, this study first discusses the recorded shaking in terms of intensity measures of structural interest. Second, using a ground motion model calibrated ad-hoc for Campi Flegrei and representing its peculiar features, it presents maps of the estimated shaking from the largest magnitude event and maps of the largest shaking considering all events. Finally, the structural response of single degree-of-freedom systems, representing code-conforming masonry and reinforced-concrete structures, are evaluated by means of non-linear dynamic analysis. Results show that structural actions close to the epicenters (i.e., less than 1 km), can be non-negligible at some vibration periods. However, ground motion attenuation is such that the largest estimated shaking, from all (Formula presented.) events, is reduced by more than 60% already at less than 4 km from the epicenters. The structural effects on code-conforming structures are generally negligible, with limited engagement of non-linear behavior only for the masonry structure and only in close proximity to the epicenter of the (Formula presented.) earthquake.