GNGTS 2019 - Atti del 38° Convegno Nazionale

274 GNGTS 2019 S essione 2.1 Our results show that maximum differences are obtained when a different period T is considered, instead that for different run up. For the evaluation of the maximum tsunami flooding using the Pignatelli et al. (2009) equation, we considered different n Manning coefficient, for different coast morphology, i.e., roughness 0.015 for a flat topography, 0.03 for rock platform and cliff area (Table 3). The comparison of the flooding data obtained with the two methods with the historical and geological data, clearly shows that the equation (2) better reproduces the observed data rather than equation (3). This because the first equation takes into account not only the run-up values but also the period, whereas the second one is strictly related to the run-up values considering the same roughness values. Indeed, with the first equation at Morghella beach, we obtained a flooding of 1235.6 m, which is comparable with the minimum flooding at this site (up to 1200 m inland), obtained by taking into account the findings of the 365 AD tsunami deposit. For the 1908 AD event, a flooding of 366.9 m, which is comparable with the one from the tsunami deposit (380 m) by Gerardi et al. (2012), is instead computed. For the tsunami scenarios, we selected three cases: (i) the relatively worst, but more rare, case obtained modelling the 365 AD tsunami (Fig. 2); (ii) the relatively most probable and frequent scenario, related to local events such as the eastern Sicily 1693 and 1908 tsunamis (Fg. 3a); (iii) a hypothesized severe scenario, obtained by modelling a run-up of 2.5 m, which is not documented by historical accounts in the study area, but reproduces the observed geological inundation north of the studied area (Fig. 3b). Table 3 - Maximum inundation obtained applying equation (3) for different coast slope and different roughness values. Date R (m) n k α X max very flat topography 365 AD 2 0.015 0.06 2.1 670.0 1693 1.2 0.015 0.06 2.1 339.6 1693 2.5 0.015 0.06 2.1 901.4 1908 1.5 0.015 0.06 2.1 457.0 flat topography 365 AD 2 0.015 0.06 5.4 667.4 1693 1.2 0.015 0.06 5.4 338.3 1693 2.5 0.015 0.06 5.4 898.0 1908 1.5 0.015 0.06 5.4 455.2 gently sloping rocky platform 365 AD 2 0.03 0.06 4.6 167.1 1693 1.2 0.03 0.06 4.6 84.7 1693 2.5 0.03 0.06 4.6 224.8 1908 1.5 0.03 0.06 4.6 113.9 sloping rocky platform 365 AD 2 0.03 0.06 11.6 164.2 1693 1.2 0.03 0.06 11.6 83.2 1693 2.5 0.03 0.06 11.6 220.9 1908 1.5 0.03 0.06 11.6 112.0 Cliff 4 m 365, 1693, 1908 4.5 0.03 0.06 8.5 26.2