When are mitigation actions warranted: the case of the 2009 L'Aquila earthquake

The disastrous earthquake in L’Aquila Italy (Mw 6.3, 6 April 2009) again highlights the issue of potentially reducing seismic risk by releasing warnings or initiating mitigation actions. Earthquakes cluster strongly in space and time, leading to periods of increased seismic hazard. During such seismic crises, seismologists typically convey their knowledge of earthquake clustering based on past experience, basic statistics and “gut feeling.” However, this information is often not quantitative nor reproducible and difficult for decision‐makers to digest. We define a novel interdisciplinary approach that combines probabilistic seismic hazard and risk assessment with cost‐benefit analysis to allow objective risk‐based decision‐making. Our analysis demonstrates that evacuation as mitigation action is rarely cost‐effective. Future mitigation strategies should target the weakest buildings and those on the poorest soil