SEISMIC AND TSUNAMI HAZARD ASSESSMENT OF A COASTAL ACTIVE FAULT CONSTRAINED WITH THE HISTORICAL CALABRIA 1905 EARTHQUAKE (SE TYRRHENIAN SEA)

Italy is one of the most seismically active regions in Mediterranean and one of the countries with the longest record of historical earthquakes in the world. Over the last decades the scientific community invested great energy and resources for seismic and tsunami hazard assessment, that can actually improve with knowledge of those active structures capable of generating destructive earthquakes and, if located offshore, also tsunamis. A more reliable hazard assessment of the exposed regions can be done if forecasting models can be constrained with instrumental or historical data. This is the case of the 1905 Calabria earthquake, which was destructive and was followed by tsunami waves. A recent geophysical survey allowed to identify an active structure, named Sant‘Eufemia Fault, located offshore within the Sant‘Eufemia Gulf (SE Tyrrhenian Sea) and facing the western Calabria. Numerous observations and models support the hypothesis that this structure could be the seismogenic source of the 1905 earthquake and, being active, capable to trigger a new event. Analyzing all available geophysical data, we defined the most credible geometry of the Sant‘Eufemia fault: 40 km length and 2.3m of slip rate. Using empirical relationships available in the literature, we assigned to this fault a width equal to 17km and the potential for an Mw 7 earthquake. Using these parameters we performed shacking scenarios imaging a fault plane with a single centered asperity and uniform Seismic Moment (M0) distribution. We produced both the Peak Ground Acceleration (PGA) and the Peak Ground Velocity (PGV) maps, that can be compared with intensities distribution of the 1905 Calabria earthquake. Seismic hazard assessment is also analyzed taking into account soils type distribution interacting with shaking. This fault is also used to perform tsunami modelling and to compare the numerical results with the historical data available on run-up and inundation. Main results:the Sant‘Eufemia fault is reasonably compatible with the historical information on the 1905 event; and an eventual tsunami wave impact on the western Calabrian shoreline is better constrained. We consider the thorough assessment of the different types of hazards associated with the Sant‘Eufemia fault as a very important result for the Tyrrhenian coasts of Calabria, which have not received so far the attention reserved to other Italian coastal areas despite the growing infrastructure facilities and tourism activities.