Incorporating paleoseismological data in PSHA: the case of Calabria (southern Italy)

Most of the seismic hazard maps developed in Italy in the past years are mainly based on the probabilistic approach, using a “de-clustered” seismic catalogue and a seismotectonic zonation. In these maps seismotectonic data are entered only in order to define the geometry of the seismogenic zones of Italy. Recently, the Seismic Survey of Italy and the National Group of Defense against Earthquakes prepared new Probabilistic Seismic Hazard maps of Italy, using the Cornell methodology. Neither did these maps take into account the geological results and the historical insights obtained in the past few years. Although some attempts in applying more refined methodologies were made (non-Poissonian behaviour of seismicity), results have often been conditioned by the scarce knowledge of seismic source characteristics (i.e., location, and seismic behaviour of faults), which are not available for most of the Italian territory. We tried to incorporate new geological data into the probabilistic seismic hazard assessment, focusing on one of the most seismically active regions of the Mediterranean (Calabria, southern Italy). This issue has been faced using data gathered through paleoseismological, historical and archeoseismological analysis performed ad hoc, which constrained (a) the geometry of the zones, (b) the parameters of earthquake-like epicenter location, magnitude, return-interval, and elapsed time. While not claiming to create a new hazard map, we highlight the influence of the geometry of seismic zones on the hazard calculation, partially redrawing the seismogenic zonation of Italy in Calabria. We obtained differences of up to 35.%, between expected peak ground acceleration values calculated with or without the parameters derived from paleoseismological data.