The 2004 Italian Seismic Hazard Model: Twenty Years On

The Italian national seismic hazard model, MPS04, was developed more than 20 years ago to provide a rational basis for regulatory applications. Since 2009, it directly provides seismic actions for structural design and assessment in the building code. MPS04 is still the official reference despite other authoritative models being developed in the meanwhile. It was also employed for research purposes and for large‐scale seismic risk analyses. Both the direct application of MPS04 for structural design and its longevity are somewhat peculiar and may thus warrant analysis. This short article retrospectively recounts: its development, the events leading to its enforcement, the implications it had on the earthquake engineering community, as well as the limitations and challenges it faced, especially due to observations following major seismic sequences that occurred in Italy since its release. The story of MPS04 is interpreted as a success one yet may have had some unintended consequences. In hindsight, on one hand, its grounding on the historical earthquake catalog, its source model based on seismotectonics, its rigorous scientific and probabilistic nature, its reproducibility in relation to its slim logic tree, and the consequent trackability, enabled gaining confidence in the main and side results. On the other hand, being the first model of its kind for Italy, and having been directly applied in codes for nearly two decades, it may have made it harder for more recent, and presumably more state‐of‐the‐art models, to take its place.