- © 2008 by the Seismological Society of America
In 2004, on behalf of the Department of Civil Protection (DPC—Dipartimento della Protezione Civile), the Istituto Nazionale di Geofisica e Vulcanologia (INGV) released a new Italian seismic hazard map. The entire scientific process was public and transparent: an international panel of experts conducted a peer review while the work was in progress, and all the input data, the final output, and the technical documentation was published. The details of the entire process are available on a dedicated Web site (http://zonesismiche.mi.ingv.it).
The new hazard map provides the expected value of horizontal peak ground acceleration (PGA) with an exceedance probability of 10% in 50 years. This elaboration was recently adopted (ordinance 3519/2006 signed by the Prime Minister) as the “reference map” for assigning municipalities to one of four seismic zones according to building-code criteria. In the building code released in 2005 (ministerial decree 14/09/2005), the seismic zone assignment criteria is the expected PGA value; for each seismic zone the code also defines a standard design spectrum anchored to a fixed PGA value allowing designers to change the anchor value of the response spectra within a 20% discretionary margin when more detailed information on the expected shaking parameters of the site of interest are available.
In addition to the scientific community, local administrators and professionals, typically civil engineers and architects, use seismic hazard values. Administrators use them to define the appropriate level of protection for the regions they oversee, while professionals refer to them to provide the best compromise between building costs and safety.
Following the publication of the reference map, the DPC financed the S1 project to produce a set of additional elaborations that would better describe the Italian seismic hazard. This resulted in a set of maps expressed in terms of PGA and Sa (spectral accelerations), both evaluated for different …