GNGTS 2019 - Atti del 38° Convegno Nazionale

272 GNGTS 2019 S essione 2.1 X i is the hypotenuse of a rectangular triangle representing the coastal area with slope α, corresponding to the mean slope taken from the sloping overland profile of the typical coast of the studied areas. At the maximum water flooding along the coast X max = Xi cosα. Considering that at the X max the wave height H i becomes nil, we can obtain the maximum flooding of the tsunami from the Noormets et al. (2004) equation: (2) For the evaluation of the maximum flooding produced by tsunamis, in addition to the previously described method we also used the Hills and Mader (1987) equation modified by Pignatelli et al. (2009): X max = ( Hs ) 1.33 * n –2 * k cosα (3) where X max = flooding limit [m]; Hs = run-up [m]; k = 0.06 (constant); α is the slope of the coast topographic profile hit by the waves; n = Manning coefficient, which represents the roughness of the coast and assumes a value of 0.015 for a flat topography, 0.03 for an urbanized area and 0.07 for a highly wooded area. For this computing we have regrouped sites according to their morphological setting into beaches with very flat (α = 2.1) and flat topography (α = 5.4); sites with gently sloping (α = 4.6) and sloping (α = 11.6) rocky platform, and sites with cliff (E = 4 and > 6 m). Results obtained with the two approaches were compared to establish the most suitable one. Tsunami inundation scenarios. We extrapolated the maximum height and period of the tsunami waves at the breaking point (run up) in the study area from the historical tsunami data (Tab. 1). Based on observed run-ups and flooding, and on the minimum inundations recovered from tsunami deposits, we note that the main tsunami events that have affected the coast between Siracusa and Capo Passero are the 365 AD Creta tsunami, the 1693 and 1908 tsunamis. Table 1 - Run-up and inundations for the 365AD, 1693 and 1908 tsunamis along the coast between Siracusa and Marina di Ragusa. Historical and calculated data (after Gerardi et al. , 2008) and tsunami deposits (after De Martini et al. , 2012; Gerardi et al. , 2012); * Lorito et al. (2008). Date Locality Lat Long Run-up (m) Inundation (m) Data type 365 AD Pantano Morghella 36.703 15.115 2 not available numerical model* 365 AD Pantano Morghella 36.703 15.115 not available 1200 geologic (deposit) 11/01/1693 Siracusa 37.082 15.285 (1.2 - 4.5) 90 historical 11/01/1693 Mazzarelli 36.465 14.331 (0.8 - 2.9) 100 historical (M. di Ragusa) 28/12/1908 Siracusa 37.082 15.285 1.20-2.0 (100) historical 28/12/1908 Siracusa (S. Panagia) 37.082 15.285 (1.20-2.0) 100 historical 28/12/1908 Avola 36.908 15.135 1.3 15 historical 28/12/1908 Calabernando 36.869 15.136 not available up 10 m historical 28/12/1908 Marzamemi 36.741 15.118 1 (80) historical 28/12/1908 Pantano Morghella 36.703 15.115 (1.0 - 3.0) 380 geologic (deposit) 28/12/1908 Capo Passero 36.682 15.135 1.5 (100) historical 28/12/1908 Pozzallo 36.682 15.135 1.5 (100) historical 28/12/1908 M. di Ragusa 36.682 15.135 1.5 (100) historical