# Joint Multi-Scenario-Based Earthquake and Tsunami Hazard Assessment for Alexandria, Egypt
## 4 Multi-Scenario Physics-Based Tsunami Hazard Analysis: Data and Methods
### Tsunami Hazard Maps for Alexandria  
Figure 12 shows maps of mean and maximum estimated tsunami wave amplitude values from aggregated tsunami scenarios for Alexandria, as described in Section 4.2. It quite clear that scenarios S6 and S7, which are situated in the EH part, are the most severe scenarios that could produce the highest hazard in terms of tsunami wave amplitude and inundation distance to the Alexandria coastal zone, with an estimated maximum tsunami wave amplitude of 6.0-6.5 m (\(\pm\)mean sea level), whereas the estimated mean of the maximum wave amplitude of all individual scenarios is about 2.5-3.0 m (Figure 12). In this work, an aggregated scenario was built using the maximum and mean tsunami wave amplitude values estimated (Figure 12) through the combining or aggregating of selected individual scenarios listed in Table 3. The aggregated scenario for Alexandria was established by merging all wave tsunami amplitude values estimated at each site along the coast in one feature class using a geographic information system (GIS) tool, and then the highest values were retained. This maximum estimated tsunami wave amplitude from individual scenarios is registered at the western coastline of the governorate. The maps of average ETA for Hellenic and Cyprus Arc scenarios are mapped and shown in Figure 13.  
Figure 11: Initial tsunami conditions (coinciding with the vertical coseismic displacement of the seabed) for the nine selected earthquake model scenarios from [PERSON] et al. [3]; the red and blue colors indicate positive and negative seawater elevations, respectively. The maps of the mean and maximum tsunami wave amplitude were adopted to establish related tsunami inundation maps using various Coefficients and empirical relationships. In this work, we decided to take tsunami intensity as a representative value of the mean and maximum wave amplitude for the segmented shoreline, and each segment has a maximum tsunami wave amplitude value from the selected--then aggregated--tsunami scenarios developed by [PERSON] et al. [3]. To keep potential local changes in wave amplitude under consideration, which can lead to locally significant exceedance mediated on the coastal area, the tsunami amplitude must be applied to a multiplying safety factor, indicated with k. This coefficient allows for the transformation of the tsunami wave amplitude in an estimate of the maximum expected run-up, here indicated as Rmax. To allow for a reliable choice of k, [PERSON] et al. [71] produced an estimate of the relationship between tsunami amplitude and the maximum run-up Rmax in some representative areas through the detailed modeling of numerous tsunamis with different features. The simplest way to define the flooded area or inundation zone is to apply a hydrostatic model, based on a set scenario run-up value, without taking into account the resistance to the ingress of the tsunami wave on land, opposed by the roughness of the ground, both natural and artificial. In this case, the flooded area is the entire coastal strip located at a level lower than the run-up. This approach is very quick and easy to implement,  
Figure 13: The average ETA for representative scenarios in the East (**a**) and West Hellenic (**b**) and Cyprian (**c**) Arcs. but, not considering the process of attenuation of the wave height inland, it can lead to a strong overestimation of the extension of the inundated areas. Therefore, it can be used for preliminary analyses on large areas and/or as a basis for orienting the choices of subsequent, more detailed processing. In this work, the inundation maps were developed by empirically taking into account the process of dissipation of the wave energy in its path on land. In practice, the method is based on the application of an empirical relationship between the scenario run-up and land penetration (Equation (1)), estimated on the basis of numerous observations conducted following recent and historical tsunami events, especially in the Pacific area (2004, 2011), but also in the Mediterranean.