Fault-Based Earthquake Rupture Forecast in Central Italy: Remarks after the L'Aquila Mw 6.3 Event

Abstract

In 2006 we published an earthquake hazard model called LASSCI (LAyered Seismogenic Source model in central Italy). In October 2008 we began to update the model for use in 5- and 10-year forecasts. The LASSCI–2006 model is supported by good fault-based definitions of seismogenic sources and simple phys- ically motivated models of earthquake occurrence; the LASSCI–2009 model has been improved by revision of the error propagation assumptions and increased accuracy of the earthquake probabilities. The 6 April 2009 earthquake that struck L’Aquila occurred on the model fault having the highest probability of occurrence in the 2009 revised LASSCI forecast: it is therefore consistent with our model assumptions. Furthermore, peak ground accelerations were in reasonable agreement with the values having 90% probability of not being exceeded in 50 yr. In the revised 2009 model, the aggregate probability of having a maximum-sized event in the next 5 yr on at least one of the neighboring sources (less than 25 km distance away) decreases in L’Aquila from 10% to 7% after the earthquake occurrence, but still remains a maximum there along the central Apennines. The LASSCI models 2006 and 2009, featuring charac- teristic fault sources and time dependence, seem to be suitable for guidance in recon- struction and seismic retrofit in the central Appenines.