GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 2.1 301 by amplifying the numerically simulated offshore tsunami through a log-normal conditional probability which gives the mean MIH. A multiplicative factor is determined from the same distribution and applied to convert the MIH into the maximum run-up, which can be 3-4 times larger. This method does not take into account dissipation during tsunami inundation. Hence, an empirical dissipation factor is introduced to limit the maximum inundation distance (Fig. 1). The dissipation factor is derived from observed data collected during post tsunami field surveys (Faser and Power, 2013, and references therein): the rather good data sets currently available suggest a reduction of the maximum wave height while penetrating inland, represented by a dissipation factor of about 1 m height every 200 m away from the coastline. A much lower dissipation is instead observed along and surrounding river estuaries, treated by means of a dissipation factor of 1 m every 400 m. By applying these parameters, we define the maximum expected inundation distance for a given maximum estimated run-up value (Fig. 1). Using a GIS-based approach, the method combines these results with a detailed DTM and computes the inundation line corresponding to the 2500 yr average return period run-up and the 84-th percentile of the model epistemic uncertainty. More details of the different steps in this method are given in Selva et al. (2016), Molinari et al. (2016), and in the implementing decrees of the SiAM Directive (DPCM, 2017). The inundation maps and the preliminary evacuation zones for the Advisory and Watch alert levels are available on the Tsunami Map Viewer - http://sgi2. isprambiente.it/tsunamimap/ (Fig. 2). The aim of the present work is to evaluate the performance of the proposed empirical method on a specific target area by comparing the empirical maximum inundations with the inundation maps obtained using the more robust tool of the numerical simulations. The selected target area is the coastal segment placed in the South-Eastern Sicily, Italy, between Catania and Siracusa (Fig. 3), two touristic and commercial urban areas, comprising harbour infrastructures and a petrochemical complex. This area has experienced destructive tsunamis in the past (e.g., 1693 and 1908) and the coast presents very different terrain morphological features (e.g., flat Fig. 2 - Screen shot of the Tsunami Map Viewer (http://sgi2.isprambiente.it/tsunamimap/ ) showing in light blue the preliminary evacuation zone for the Watch alert level in the Syracuse coastal area. The purple line indicates the -50 m bathymetry.