# Probabilistic Seismic Hazard Assessment of the Southwestern Region of Saudi Arabia
## 3 Results and Discussion
Farasan, Jazan, Al Qunfudhah, Al Lith, and Al Birk present the highest seismic hazard values out of all the cities under investigation according to both the graphical representation (Figure 6) and the hazard values listed in Table 2. The equivalent pairs of SAmax for these five cities are 0.27 and 0.41 g, 0.12 and 0.17 g, 0.10 and 0.15 g, 0.08 and 0.14 g, and 0.07 and 0.12 g, respectively, for both the 475 and 975 years under B/C site conditions. These cities display SAmax pair values for the same return periods of 0.37 and 0.52 g, 0.15 and  
Figure 6: UHS, for return periods of 475 and 975 years, taking into account B/C and C NEHRP soil classes, and for a 5% damping ratio. 0.22 g, 0.14 and 0.19 g, 0.13 and 0.17 g, and 0.10 and 0.15 g, respectively, under the C soil classification. Notably, oscillation periods ranging from 0.10 to 0.75 s were observed for the SAmax hazard values for locations under examination (refer to Table 2). A brief comparison of PGA values obtained from our research is given in Table 3 for some of the chosen cities, for B/C soil conditions and a 475-year return period. These results are compared to PGA values from earlier research by [20; 101]. To be specific, the authors of [20] devised and validated a framework for conducting PSHA in the Kingdom of Saudi Arabia. Their approach employed Monte Carlo simulation and included the development of seismic source zone models encompassing 43 zones. They utilized four distinct GMPEs for active shallow crustal sources [80; 102; 103; 104], while [101] conducted a seismic hazard analysis for Saudi Arabia using a Monte Carlo approach and a spatially smoothed seismicity model. They also employed the same four GMPEs for active shallow crustal sources [80; 102; 103; 104], given equal weights in the established logic tree. Additionally, they used the model in [82] for stable continental regions, and the model in [105] for extensional zones in the Red Sea and Indian Ocean. Differences in the seismicity characteristics, the particular seismic source model(s) used, the GMPEs used, the final logic tree's composition, and the weights associated with its components are the main causes of the observed discrepancies. In light of these variations, we support an alternative strategy [99; 100] to create a design spectrum specific for certain cities in this area. These design spectra use only two ground motion parameters: the SA (0.2 s) and SA (1.0 s) values. Several studies have previously used this approach to create a representative design spectrum (e.g., ref. [106] for Andaman, ref. [74] for Egypt, ref. [70] for Mexico, and [1] for Peru and Chile). This process is recommended for some chosen cities in the current study (see Figure 7) and two identified NEHRP soil classifications (B/C and C), with a 475-year return period. Interestingly, the design spectra obtained in this manner, as shown in Figure 7, show a significant degree of consistency and closer match with estimated UHS. This method typically produces conservative results, particularly when fitting the calculated UHS values. Lastly, we want to shed light on any potential relationships between the seismic hazard estimates that has been obtained throughout our evaluation. Specifically, we examine the PGA values for the computed site classes (see Figure 8) and the average PGA and SAmax values that were obtained for the two computed return periods. The methods described in earlier research, including those in [107] for Algeria, ref. [74] for Egypt, and [70] for Mexico, were used to assess these correlations. A strong linear association can be seen in the regression studies between the calculated site conditions and the obtained PGA or SAmax values for the same return periods (Figure 8). This suggests that, regardless of soil conditions, the mean PGA or SAmax values for a 975-year return period are roughly 1.4 to 1.5 times the corresponding ones for a 475-year return period, which is in line with findings from the previously mentioned studies [70; 74; 107].