Ground Motion Models for Campi Flegrei (Italy)

Ground Motion Models (GMMs) are empirically-calibrated equations relating ground motion intensity measures to earthquake magnitude, source-to-site distance, geological local site conditions, and possibly other covariates. GMMs are employed for applications such as probabilistic seismic hazard analysis and post-event rapid shaking estimation. Since early 2014, the densely populated Campi Flegrei caldera in Southern Italy has experienced increasing seismicity, concomitant to the volcanic unrest and ground uplift, with over ten thousand recorded events, with duration magnitude larger than -1.1. In the period between March 2022 and May 2024, seismic activity has intensified, including approximately seventy events with duration magnitudes between 2.5 and 4.4, most of them widely felt, in some cases causing non-negligible seismic structural actions close to the source, and ultimately sparking large public concern. In this study, we calibrated site-specific GMMs for peak ground acceleration, peak ground velocity, and 5% damped spectral pseudo-acceleration for 18 vibration periods ranging from 0.02 s to 5 s. The dataset includes recordings from the largest events over the period 03/22-05/24 recorded by more than 50 accelerometric and velocimetric seismic stations at epicentral distances Repi < 40 km. Moment magnitude, which is the scale used in the GMMs, was derived for the events from their displacement Fourier amplitude spectrum. The GMMs show structurally non-negligible spectral amplitudes at short periods ( T<0.2 s), and the relatively faster attenuation with distance Repi[[EQUATION]]5 km as compared to some existing ground motion models for Italy.