# Probabilistic Seismic Hazard Assessment of the Southwestern Region of Saudi Arabia
###### Abstract  
In relation to its rapid infrastructure expansion, exemplified by projects like the Najran Valley Dam or the rehabilitation of agricultural terraces, Saudi Arabia stands out among the Arabian Gulf nations. To mitigate the earthquake-related risks effectively, it is imperative to conduct an exhaustive analysis of its natural hazards. The southwestern region of Saudi Arabia is the main subject area of this study for the probabilistic seismic hazard assessment (PSHA), which aims to identify the peak ground acceleration (PGA) and spectral acceleration (SA) values. The investigation encompasses a 10% and 5% probability of occurrence over a 50-year exposure time for both B/C and C NEHRP soils. In order to take into account the earthquake activity that takes place in the vicinity of the Red Sea Rift, which in fact may have an impact on the seismic hazard in this active tectonic region, different seismic source zones were especially designed for this evaluation. Various characteristics such as the uncertainties related to the \(b\)-value, the expected maximum magnitude, and different ground motion prediction equations (GMPEs) were integrated using a logic tree scheme. Additionally, regression relationships between the computed ground motion values were established, and a novel design response spectrum was developed and recommended for several cities. Regarding the key findings, it is significant to highlight that the seismic hazard decreases towards the northeast, when moving away from the Red Sea Rift, confirming anticipated trends where proximity to the rift corresponds to increased seismic hazard. Notably, cities such as Farasan Island, Jazan, Al Qunfundhah, Al Lith and Al Birk present the highest observed hazard values among all the cities analyzed. For these cities, the obtained maximum SA values for both 475 and 975 years under B/C site conditions are as follows: 0.268 g and 0.412 g, 0.121 g and 0.167 g, 0.099 g and 0.150 g, 0.083 g and 0.135 g, and 0.066 g and 0.118 g, respectively. These results emphasize the crucial necessity of adequately evaluating and thoroughly updating the seismic hazard inherent to these particular areas to enhance the risk reduction and disaster readiness initiatives. e 2024 23 July 2024 23 July 2024 28  
inclusion in building regulations. These assessments, in turn, serve as the foundation for creating, refining, or amending seismic design codes in the region under consideration [1; 2; 3]. This approach aligns with the broader objective of enhancing the resilience of communities and infrastructures to seismic risk. The Red Sea rifting, a very notable and active tectonic process along the boundary between the Nubian and Arabian Plates, significantly impacts the seismotectonic environment in southwest Saudi Arabia. From the Gulf of Aden and the Afar Triple Junction in the south to the Dead Sea Transform Fault in the north, this tectonic structure stretches [4] (Figure 1). This dynamic and geologically active region began to form around 30 million years ago (late Early Oligocene) in the eastern Gulf of Aden. The tectonic activity in this region was marked by significant volcanic activity and the formation of rift valleys, highlighting the ongoing process of seafloor spreading and continental rifting [5; 6; 7; 8; 9; 10; 11]. The Nubian and Arabian tectonic plates converge to form a seismically active and dynamic region. Prominent faults like the Najd Fault system are the outcome of the intricate current interaction between the Nubian Plate and the Arabian Plate. The western Gulf of Aden, the central and southern Red Sea, and the Arabian Shield surrounding activity all have an impact on the southwest, which includes places like Asir, Jazan, and Al-Bahah. Each of these geological characteristics adds to the region's seismic hazard. The authors of [12] explore the seismicity and crustal deformation in the area, providing insight into the complex tectonic features that characterize the seismotectonic environment of southwest Saudi Arabia.