Abstract
The NEAM Tsunami Hazard Model 2018 (NEAMTHM18) is a probabilistic hazard model for tsunamis generated by earthquakes. It covers the coastlines of the North-eastern Atlantic, the Mediterranean, and connected seas (NEAM). NEAMTHM18 was designed as a three-phase project. The first two phases were dedicated to the model development and hazard calculations, following a formalized decision-making process based on a multiple-expert protocol. The third phase was dedicated to documentation and dissemination. The hazard assessment workflow was structured in Steps and Levels. There are four Steps: Step-1) probabilistic earthquake model; Step-2) tsunami generation and modeling in deep water; Step-3) shoaling and inundation; Step-4) hazard aggregation and uncertainty quantification. Each Step includes a different number of Levels. Level-0 always describes the input data; the other Levels describe the intermediate results needed to proceed from one Step to another. Alternative datasets and models were considered in the implementation. The epistemic hazard uncertainty was quantified through an ensemble modeling technique accounting for alternative models’ weights and yielding a distribution of hazard curves represented by the mean and various percentiles. Hazard curves were calculated at 2,343 Points of Interest (POI) distributed at an average spacing of ∼20 km. Precalculated probability maps for five maximum inundation heights (MIH) and hazard intensity maps for five average return periods (ARP) were produced from hazard curves. In the entire NEAM Region, MIHs of several meters are rare but not impossible. Considering a 2% probability of exceedance in 50 years (ARP≈2,475 years), the POIs with MIH >5 m are fewer than 1% and are all in the Mediterranean on Libya, Egypt, Cyprus, and Greece coasts. In the North-East Atlantic, POIs with MIH >3 m are on the coasts of Mauritania and Gulf of Cadiz. Overall, 30% of the POIs have MIH >1 m. NEAMTHM18 results and documentation are available through the TSUMAPS-NEAM project website (http://www.tsumaps-neam.eu/), featuring an interactive web mapper. Although the NEAMTHM18 cannot substitute in-depth analyses at local scales, it represents the first action to start local and more detailed hazard and risk assessments and contributes to designing evacuation maps for tsunami early warning.
Highlights
Tsunamis can be triggered by earthquakes, landslides, volcanic processes, meteorological events, and asteroid impacts
We recall that the NEAMTHM18 deals with earthquakegenerated tsunamis and that it is a time-independent hazard model, as the earthquake occurrence is modeled as a Poisson process
As the output of Step-4, the model is constituted by a collection of hazard curves, one set per Points of Interest (POI), and hazard and probability maps derived from these curves
Summary
Tsunamis can be triggered by earthquakes, landslides, volcanic processes, meteorological events, and asteroid impacts. In the last 10–15 years, the techniques for computation-based PTHA, which is based on multiple tsunami numerical simulations starting from a probabilistic source model, have progressively evolved after the seminal works by Lin and Tung (1982) and Rikitake and Aida (1988). These authors extended the methods introduced at the end of the 60s for PSHA (Esteva, 1967; Cornell, 1968), recently reviewed by McGuire (2008) and Gerstenberger et al (2020), to tsunamis (Geist and Parsons, 2006; Geist and Lynett, 2014; Grezio et al, 2017; Mori et al, 2018). The availability of modern HPC has made computational tsunami hazard assessment feasible at a global scale while retaining relatively high-resolution and extensive exploration of source uncertainty (Davies et al, 2018; Davies and Griffin, 2020)
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