# Joint Multi-Scenario-Based Earthquake and Tsunami Hazard Assessment for Alexandria, Egypt
## 3 Multi-Scenario Physics-Based Seismic Hazard Analysis
### Maximum Credible Seismic Input (MCSI)  
The MCSI response spectrum is calculated based on the methods described by [PERSON] et al. [51]. Multiple rupture scenarios are considered stochastic realizations for each seismogenic source, which are defined in terms of magnitude, location, and focal mechanism.  
\begin{table}
\begin{tabular}{c c} \hline
**Epicenter (Lon, Lat)** & **(25.63\({}^{\circ}\), 35.18\({}^{\circ}\))** \\ \hline Magnitude & 8.5 Mw \\ \hline Hypocentral depth & 20 km \\ \hline Ep. distance from Alexandria & 609 km \\ \hline Strike, dip, rake & 115\({}^{\circ}\), 45\({}^{\circ}\), 110\({}^{\circ}\) \\ \hline \end{tabular}
\end{table}
Table 2: Source parameters of the August 1303 earthquake [35].  
Spectral acceleration values (SA) are computed at various periods (0-4.0 s), and the maximum median value is selected, as illustrated in Figure 8a-d. In such a way, the MCSI represents a reliable estimation of the upper-bound level of shaking that could occur at a selected site (not considering their probability of occurrence), usefully summarizing the information contained in the multitude of time histories considered in the NDSHA for engineering analysis.  
Figure 8: \(Cont.\)  
Figure 8: MCSI response spectra at four selected sites: 2 (**a**), 3 (**b**), 28 (**c**) and 47 (**d**). The gray band represents the MCSI, as defined by [PERSON] et al. (1998), which is controlled (at various periods) by the sources reported and described in each of the underlying tables. Each colored line represents a response spectrum for an earthquake scenario that contribute to the MCSI response spectra, and each source parameter is indicated in the table below the graph. The tables below the graphs show different seismogenic source numbers affecting the selected site, along with its magnitude (Mw), epicentral distance (edi), depth, strike, dip, rake, source receiver angle (ser), site longitude (slon), and site latitude (slat). The solid line represents the median, and the shaded area shows the 95 th percentile (i.e., median + 2\(\sigma\)).  
In this study, the MCSI was computed at bedrock (i.e., soil class A with \(\text{Vs}_{30}\geq 800\) m/s, according to Eurocode 8 [52], with a 10 Hz cutoff frequency for the sites shown in Figure 4. Due to the complexity of the rupture process on a fault (and the implicit impossibility to deterministically predict a future one), one hundred kinematic realizations were considered in the analysis. An example of the results is shown in Figure 8, where the MCSI evaluated at selected sites (i.e., [2; 3; 23; 42]) along the shoreline of Alexandria are shown, with the median and 95 th percentile.  
For site 47 (Figure 8d), three seismogenic sources contribute to its MCSI, and the maximum spectral acceleration is 0.27 g and 0.45 g for median and median + 2\(\sigma\), respectively, at a 0.2 s spectral period. The maps with the maxima MCSI spectral acceleration values (95 th percentile) at two selected periods (T = 0.5 s and T = 1.0 s) for the considered sites are shown in Figure 9.