The power of the little ones: Computed and observed aftershock hazard in Central Italy

Seismic hazard in Central Italy due to the 2016-2017 seismic sequence is modeled using a standard probabilistic aftershock seismic hazard model. Two key features of the model are the consideration of time-dependent aftershock occurrence, modeled by stacking Omori decay curves associated with the three largest (M-w > 5.5) events, and the incorporation of geologic information by modeling the locations of expected seismicity along realistic fault surfaces. The computed seismic hazard at Amatrice indicates higher hazard values compared to those computed using a conventional time-independent hazard analysis. We then compare the computed hazard curves against empirical hazard curves constructed for 12 individual recording stations in terms of peak ground acceleration, each with at least 35 (and up to 231) recordings. At eight sites, the observed exceedances fall within one standard deviation of the expected mean, while at the remaining sites, the observed exceedances fall outside this range indicating a poorer match. The soil sites are among the stations with the poorest match, suggesting that site effects may not be accurately modeled with the current approach.