The assessment of earthquake hazard in Italy: a review

We present a review of the assessment of earthquake hazard in Italy, with special reference to the relationships between hazard models and building codes. After early attempts at hazard assessment in the 19th century, the 28 December 1908, Messina Straits earthquake prompted the inception of the first national seismic legislation, passed in early 1909. Nevertheless, the official building code started to be based on a truly scientific background only after 1980, when the catastrophic Irpinia (southern Italy) earthquake forced the qualified authority to accept a science-based assessment (statistics on the earthquake catalogue data) to support the implementation of the new national seismic zonation. Later on, between 1985 and 2000, the two basic components of seismic hazard assessment, namely the earthquake record and the distribution of earthquake sources, were greatly developed through investigations carried out by the Gruppo Nazionale Difesa dai Terremoti and by the Istituto Nazionale di Geofisica. Along with the improvement of basic data, the Italian seismological community started developing a new hazard model (PS4), based on the concept of seismotectonic probabilism, aimed at supplying the Italian Government with a solid reference frame for updating the seismic zonation and building code. Nevertheless, this goal was achieved only two decades later: on 31 October 2002 a moderate-size earthquake caused the death of 27 children and a teacher in a collapsed school of southern Italy, forcing the qualified authority to take a major step of modernization for the second time in 22 years. The entire Italian territory, including areas of rare and sparse seismicity, was subdivided into four seismic zones, mainly on the basis of PS4 results. In 2004, the Italian seismological community developed MPS04, a fully updated hazard model that was initially conceived only in view of updating the seismic zonation. In 2007, MPS04 was extended to provide design spectra for a new building code, which was finally adopted in 2009, following the disastrous L’Aquila (central Italy) earthquake. The experience of the European project for seismic hazard assessment named SHARE, completed in 2013, represented a step forward and put the basis for a new project, termed MPS19, designed specifically to provide a sound basis for updating the  Italian building code.