One-second-lead earthquake warning and impact assessment at Campi Flegrei.

Rapid dissemination of earthquake information during seismic crises is crucial for mitigating the impact of earthquakes, particularly in densely populated volcanic areas, such as the Campi Flegrei caldera (Southern Italy). This region is affected by recurrent bradyseism and shallow seismicity, with recent events up to Md 4.6, very well perceived by the local inhabitants and increasing concern among the local community. In such small regions, conventional Earthquake Early Warning (EEW) systems face physical limitations, due to the short epicentral distances and relatively small magnitudes of the earthquakes. Here we propose and offline tested a hybrid, impact-based, on-site EEW system capable of providing rapid estimates of the earthquake size and expected impact (PGV, PGA), within one second after the P-wave detection. In addition, the proposed system extends the classical concept of an on-site EEW approach by introducing the notion of an area of competence (AoC): a circular zone surrounding the recording site in which peak ground motion is expected to fall within a user-defined range around the predicted value, and within which local users or infrastructures can effectively benefit from the warning. The proposed methodology is easily transferable to other volcanic or seismically active regions and might represent a step toward low-latency, impact-based earthquake alert systems designed to enhance community resilience.