GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 2.1 285 MAXIMUM INUNDATION WAVE HEIGHT BY TSUNAMIS FROM EARTHQUAKE AND LANDSLIDE SOURCES: A DISCUSSION ON METHODOLOGICAL ASPECTS A. Armigliato 1 , G. Pagnoni 1 , M.A. Paparo 1 , F. Zaniboni 1 , S. Lorito 2 , F. Romano 2 , M. Volpe 2 , R. Basili 2 , S. Tinti 1 1 Dipartimento di Fisica e Astronomia, Alma Mater Studiorum - Università di Bologna, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia (INGV), Roma, Italy Italian peninsula a hazard to be seriously taken into account. This is also confirmed by recent hazard assessments such as TSUMAPS-NEAM (http://www.tsumaps-neam.eu/) . Hazard assessment requires a well-structured approach including: 1) the identification and characterization of the sources that can have the potential to generate tsunamis in the future, 2) the availability of detailed and reliable topo-bathymetric datasets, 3) the development and application of suitable methodologies to quantify the physical observables relevant for both scientific and civil protection purposes, and 4) a properly defined strategy to assess the uncertainties to be associated to the final results (e.g. Selva et al. , 2016). Particularly as far as the tsunami inundation phase is concerned, the definition of the most appropriate methodology, which may include both numerical models, solving the equations describing the physics of the phenomenon, and simplified empirical or semi-empirical approaches is a matter of debate in the international and national communities involved in tsunami research (e.g. Løvholt et al. , 2012; Lorito et al. , 2015; Gailler et al. , 2018). This paper represents a joint effort to tackle some aspects of the problem in a harmonized way and to find the answers to a number of questions which are not only relevant from the scientific point of view but may also have decisive implications for vulnerability and risk assessment, land planning and civil protection. The occasion for starting such a discussion was the “SPOT” project (Sismicità Potenzialmente innescabile Offshore e Tsunami; Di Bucci et al. , 2017), financed by the Italian “Ministero dello Sviluppo Economico” (MISE). One of the main goals of the project was to quantify the maximum wave elevation expected along the whole Italian coastline for tsunamis generated by both selected tectonic (earthquakes) and landslide sources. The computation of detailed inundation maps for the entire Italian coastline is a prohibitive task that, in case of unavailable high-resolution topo-bathymetric models, and of limited financial and computational resources, implies the adoption of simplified but still rigorous approaches. The main question that we try to find an answer to is: can a “standardized” methodology be developed, applicable to any tsunamigenic source and target coastal area, or must we proceed in a case-by-case perspective? This contribution is a snapshot of a work in progress that, so far, led to the agreed adoption of the following methodology. 1. A reference bathymetric dataset and a reference coastline is selected: we chose the most recent version of the EMODnet (2018) database and of the ISTAT (2015) coastline. 2. As regards tsunami generation, the Okada (1992) formulae are used to compute the tsunami initial condition in the case of earthquakes, while the Lagrangian model UBO- BLOCK (see Tinti et al. , 1997; Zaniboni et al. , 2016 for a detailed description) is applied to compute landslide dynamics and associated tsunami excitation. 3. Well-established and benchmarked numericalmodels solving theNavier-Stokes equations in the shallow-water approximation are used to compute the tsunami propagation from the source to a given reference bathymetric isoline in the nearshore region (e.g Tsunami- HySEA, Macías et al. , 2017). 4. The simulations are carried out over computational grids with spatial resolutions suitable for wavelengths typical of earthquake- and landslide-generated tsunamis, which may differ from case to case. 5. The amplification of the tsunami waves from the selected bathymetric isoline up to the coastline is calculated by means of the Green’s law: for this purpose, the coastline is assigned a reference depth of 1 m.