GNGTS 2022 - Atti del 40° Convegno Nazionale

294 GNGTS 2022 Sessione 2.2 GROUND MOTION SIMULATIONS OF THE HISTORICAL FABRIANO (1741, Mw=6.17) AND CAMERINO (1799, Mw=6.18) EARTHQUAKES (CENTRAL ITALY) V. Gironelli 1,2 , T. Volatili 1 , L. Luzi 3 , G. Brunelli 1,3 , M. Zambrano 1 , E. Tondi 1,2 1 School of Science and Technology – Geology Division, University of Camerino, Italy 2 National Institute of Geophysics and Volcanology, Rome, Italy 3 National Institute of Geophysics and Volcanology, Milan, Italy The determination of the ground-shaking induced by destructive earthquakes is becoming a crucial aspect in the analysis of the seismic hazard assessment. The increasing importance in addressing the ground motion is related to the evaluation of the seismic site response in case of earthquake occurrence to plan the appropriate emergency activities, especially in areas characterised by an intense seismic history, as the Italian territory. Peninsular Italy has a long-term seismicity testified by one of the most complete and historically extensive seismic catalogues in the World. Specifically, the high seismic activity of central Italy is broadly documented by seismic records since historical times. Recent seismicity is testified by three destructive seismic sequences which struck central Apennines with moderate to significant mainshock magnitudes (5.7 ≤ Mw ≤ 6.5), the 1997 Colfiorito, the 2009 L’Aquila and the 2016-2017 Central Italy sequences. Seismic hazard studies aimed at the ground motion assessment in earthquake scenarios are based on the seismological parameters reported in the instrumental seismic catalogues. Currently, there are powerful applications like the software package ShakeMap® developed by the U. S. Geological Survey Earthquake Hazards Program (Wald et al. , 2005) which, through an interpolation algorithm, exploits the instrumental data to rapidly assess the intensity of the ground shaking generated by the earthquake. However, the accuracy of these tools diminishes in estimating the ground motion for poorly constrained events like historical earthquakes due to the increasing number of uncertainties (i.e., absence of strong motion records, estimated magnitudes and epicenters location, unknown or debated seismogenic sources, etc.). Besides the disadvantages associated with the pre-instrumental seismicity, the uncertainty associated with the local site conditions imposed is the crucial aspect of this procedure. In this study, we propose an alternative approach for generating ground motion simulations through a Geographical Information System (GIS) to ensure a more flexible customisation of the input parameters relatively designed for specific study cases. A parameter to account for the local site amplifications, is the average shear wave velocity of the uppermost 30 m (Vs,30), (FEMA 273, 1997). In this work, we created a Vs,30 map of the Umbria and Marche regions, integrating data of the local near-surface from the Italian seismic microzonation dataset. A total of 4154 Vs profiles, from geophysical tests (i.e., Down-Hole, Cross-Hole , SAWS, MASW, REMI etc. ), have been analysed to calculate the Vs,30. The spatial distribution of Vs,30 was performed based on the 1:100.000 geological map of Italy (Amanti et al. , 2002). For the sake of simplification, we adopted a new classification grouping similar geological formations in terms of lithological characteristics. Along with the Vs,30 data, this hybrid raster map has been compiled assigning to each measurement the relative slope value, derived from a 30 m resolution DEM, taking advantage from the approach of Wald and Allen (2007). Finally, a statistical analysis was performed to evaluate any dependency among Vs,30, lithology, and topography. The results show that the Vs,30 is primarily controlled by lithological aspects (Fig. 1). Consistently, the more competent limestone geologic formations are characterised by high Vs,30 median values (600-800 m/s), whereases marly/clayish rocks and quaternary deposits report low Vs,30 median values (300-500 m/s). The workflow presented in this study was applied to examine the two largest historical events that affected the central Italy during the 18 th century: the Fabriano (1741, Mw=6.17,