# Probabilistic Seismic Hazard Assessment of the Southwestern Region of Saudi Arabia
## 4 Summary and Conclusions  
The current research assesses the southwest Arabian Shield's seismic hazard, an area prone to earthquakes bordering the Red Sea, using the geophysical, geological, and seismological data that are currently available. Tectonic movements and volcanic activity are clearly visible in this area, with a particular relationship to the creation of the Red Sea and its subsequent geological changes. These elements raise the seismic hazard for significant infrastructure in this region's urban areas, such as dams and power plants. The many topographic features in northern Yemen and southwest Saudi Arabia provide proof of this complexity. Most of the earthquake activity is concentrated around the Red Sea Rift and related transform faults, according to an analysis of the available earthquake data and focal mechanism solutions. Evaluating seismic hazard is a crucial and practical step in reducing  
Figure 8: Fit of obtained ground motion data to a straight line passing through the origin (s stands for the slope). Figure 7: The estimated design spectra (for a 5% damping ratio) for several cities using the [100] criteria, compared to the UHS for the B/C and C classes, both for a 475-year return period. related risks. It is necessary to conduct a thorough and updated seismic hazard evaluation in order to support informed risk reduction and disaster preparedness efforts in the region, given the historical seismic activity and the significant implications for densely populated and economically crucial regions within the study area. This study presents an updated PSHA with the goal of providing an exhaustive, well-coordinated, and trustworthy study. For accuracy and inclusivity, this evaluation uses a well-defined seismogenic source model. A logic tree technique is used to address any potential uncertainties about Gutenberg-Richter \(b\)-values and Mmax. Other recently published GMPEs are also taken into consideration. This assessment represents an overall improvement as it presents seismic hazard in a more realistic and complete way by incorporating a variety of models and allows for the inclusion of different uncertainties. The seismic hazard results are shown here in terms of the ground motion parameters PGA and SA, corresponding to 475- and 975-year return periods, respectively (10% and 5% exceedance rates, within a 50-year exposure period). According to the NEHRP soil classes, two site conditions--B/C and C--are covered by these values. Two site conditions were taken into consideration while computing seismic hazard curves for a subset of 11 important cities over the whole study region. We also calculated the UHS for the two chosen soil types and the selected return periods. As a result, it is recommended to include the suggested changes into the current Saudi Building Codes. These changes would involve adding the updated seismic design spectrum tailored for a specific location and updating the region's seismic hazard zoning maps. By using recently published globally recognized GMPEs, applying a logic tree approach, and incorporating state-of-the-art methodologies to define and characterize potential seismic sources in the vicinity, we are confident that this assessment serves as an updated input for seismic regulations in southwestern Saudi Arabia. The format of the necessary ground motion data provided by this study complies with international and European construction rules. The findings obtained here emphasize the need to update Saudi Building Codes to improve the seismic safety of critical infrastructures, including power plants and dams. These recommendations aim to enhance the resilience of structures against seismic events specific to Saudi Arabia's geological context. The process for integrating these changes into the building codes would likely involve thorough consultation with experts in seismology and structural engineering, followed by rigorous testing and validation of the proposed design spectrum.