Uncertainty in early warning predictions of engineering ground motion parameters: what really matters?

From the engineering perspective, the effectiveness of earthquake early warning systems (EEWS) depends only on the possibility of immediately detecting the earthquake and estimating the expected loss at a location of interest, in order to undertake actions to manage/mitigate the risk before the strike. The simplest proxy for the earthquake's destructive potential is the peak ground acceleration (PGA), which is predicted through probabilistic seismic hazard analysis in the framework of EEW. In this paper, the effects of different sources of uncertainty on the prediction of PGA are assessed with reference to the ISNet (Irpinia Seismic Network) EEWS. First the analyses show how the uncertainty of the ground motion prediction equation (GMPE) dominates those of magnitude and distance, almost independently of the information available for the event. Secondly, based on these findings, information-dependent lead-time maps are provided for the Campania (southern Italy) region. Finally, different real-time magnitude estimators are compared in terms of errors in the prediction of PGA, as a more efficient estimator may give additional lead-time for risk reduction.