Ozer Sozdinler, Ceren

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.

In this study, time-dependent probabilistic tsunamihazard analysis (PTHA) is performed for Tuzla, Istanbul, inthe Sea of Marmara, Turkey, using various earthquake sce-narios of Prince Island Fault (PIF) within the next 50 and100 years. The Monte Carlo (MC) simulation technique isused to generate a synthetic earthquake catalogue, whichincludes earthquakes having moment magnitudes betweenMw6.5 and 7.1. This interval defines the minimum and max-imum magnitudes for the fault in the case of an entire faultrupture, which depends on the characteristic fault model.Based on this catalogue, probability of occurrence and as-sociated tsunami wave heights are calculated for each event.The study associates the probabilistic approach with tsunaminumerical modeling. The tsunami numerical code NAMIDANCE was used for tsunami simulations. According to theresults of the analysis, distribution of probability of occur-rence corresponding to tsunami hydrodynamic parameters isrepresented. Maximum positive and negative wave ampli-tudes show that tsunami wave heights up to 1 m have 65 %probability of exceedance for the next 50 years and this valueincreases by 85 % in the Tuzla region for the next 100 years.Inundation depth also exceeds 1 m in the region with proba-bilities of occurrence of 60 % and 80 % for the next 50 and100 years, respectively. Moreover, probabilistic inundationmaps are generated to investigate inundated zones and theamount of water penetrated inland. Probability of exceedanceof 0.3 m wave height ranges between 10 % and 75 % accord-ing to these probabilistic inundation maps, and the maximuminundation distance calculated in the entire earthquake cata-logue is 60 m in this test site. Furthermore, synthetic gaugepoints are selected along the western coast of Istanbul by in-cluding Tuzla coasts. Tuzla is one of the areas that showshigh probability exceedance of 0.3 m wave height, which isaround 90 %, for the next 50 years while this probabilityreaches up to more than 95 % for the next 100 years.