# Probabilistic Seismic Hazard Assessment of the Southwestern Region of Saudi Arabia
## 2 Methodology
### Seismic Source Model  
For this assessment, two previous source models were considered after carrying out some modifications, those in [33] for Ethiopia and those in [34] for the Arabian Peninsula. Given the two seismic source models mentioned above, we aimed to refine and adapt the boundaries of these sources based on our geological and structural understanding of the Red Sea Rift. Previous models were originally designed for regional assessments of the Arabian Peninsula and Ethiopia; therefore, we adjusted the boundaries of seismic sources on both sides of the rift and meticulously reviewed seismicity parameters to ensure accuracy and relevance to our specific study area. Leveraging a unified earthquake catalog [42] alongside additional geological, tectonic and seismic crustal data, Ref. [34] proposed and characterized a source model for the Arabian Peninsula. The current study's focal area is between 16\({}^{\circ}\) and 21\({}^{\circ}\) N latitude and 39\({}^{\circ}\) and 45\({}^{\circ}\) E longitude. Eleven seismic sources previously identified in [34] were considered, modified, and included as potential contributors to hazard in southwest Saudi Arabia. These sources are shown in Figure 2 and described in Table 1. They are designated as S38 to S49 and S57. Additionally, three additional zones (S02, S03, and S06) were considered and modified based on [33], a study on seismic hazard in Ethiopia. This was carried out to account for potential seismic hazard resulting from activity west of the Red Sea Rift. Below, we offer an overview and characteristics of the seismic sources considered. Figure 2: Considered seismic source model, adapted from [33; 34], illustrating seismic activity in the left plot and solutions for focal mechanisms in the right plot [42]. Labels “NF: pure normal, SS: pure strike-slip, TF: pure thrust, NS: pure normal with a strike-slip component, TS: thrust with a strike-slip component, and U: undefined” stand for the different focal mechanisms. The majority of the Hijaz terrane, which is characterized by surface lineaments generally oriented in a NW-SE orientation parallel to the axis of the Red Sea, is included in the Hijaz seismic source, designated as S38. There have been recent as well as past seismic events in this region. Seismic activity in this source, including that which occurred during 1256, 1293, and 2009, is significantly associated with volcanic phenomena (e.g., volcanic activity at Harrat Lunier). The Jeddah seismic source, named S39, is distinguished by its northeast-trending surface fault lines running parallel to the Red Sea's transform faults. This northeast-trending structure is controlled by the Ad-Damm Fault, which reaches beyond Al-Taif from the coastal plain. Ref. [57] proposed that this fault has presented right-lateral movement since the Precambrian. The activity of the fault is supported by data from the Saudi National Seismic Network's micro-earthquake records and the studies conducted in [15]. This fault has been linked to several past earthquakes with magnitudes close to M 5.0. The S40 Tihama seismic zone covers a large portion of the Asir geological terrane and is located north of the Jizan seismic source (S41). It can be identified by its N- and NE-trending lineaments, which display complex strike-slip, normal, and reverse faulting patterns [58]. Delineating the northern boundary of this source is the Ad-Damm Fault. The Yemen volcanic trap series and the Arabian Shield are split apart at their southern boundary by the Jizan seismic source, named as S41. Because of its relatively higher seismic activity, it differs from its nearby northern seismogenic zone. The Oligocene- Miocene rifting processes located in the Red Sea and volcanic events are responsible for the earthquake's activity in this area. The most significant recorded earthquake in this region was on January 11, 1941 (Mw 6.2). Furthermore, this seismic source contains a seismic sequence that included an ML 5.1 event on 23 January 2014 [59].