Probabilistic seismic hazard assessment at bedrock conditions for the Jizan Region, Southwestern Saudi Arabia

Abstract

The current work presents a probabilistic seismic hazard assessment (PSHA) for engineering bedrock conditions (Vs30} = 760 m/s) across the Jizan region of southwestern Saudi Arabia. For this purpose, we compiled a homogenised earthquake catalogue covering 827–2022 CE, including historical and instrumental records from multiple authoritative sources. All magnitude types are converted to moment magnitude (Mw) using orthogonal regression. After declustering and completeness analysis, we defined eight area-source zones to represent the tectonic variations of the Red Sea rift, the Gulf of Aden, the Arabian Shield, and adjacent Yemeni crustal domains. Seismicity in each zone was characterised with a doubly truncated Gutenberg–Richter model. The maximum magnitudes were estimated using the Kijko–Sellevoll–Bayes approach. To account for epistemic uncertainty in ground-motion attenuation, we employed a logic tree with four GMPEs weighted equally: Abrahamson et al. (2014), Akkar et al. (2014), Chiou and Youngs (2014), and Zhao et al. (2006). Resulting bedrock hazard maps show a clear north–south gradient across Jizan. For a 475-year return period (≈ 10% in 50 years), PGA rises from ∼0.03 g in northern districts to ∼0.06 g near the Yemeni border; for a 2,475-year return period (≈ 2% in 50 years), PGA increases from ∼0.06 g to ∼0.13 g. A site-specific Uniform Hazard Spectrum for the Baish development area indicates a peak spectral acceleration of ∼85 cm/s² at T ≈ 0.2 s for the 475-year return period and ∼165 cm/s² for the 2,475-year return period. These results indicate that seismic demand in Jizan is controlled primarily by extensional deformation of the southern Red Sea and active crustal deformation in western Yemen. The study provides a robust bedrock-hazard baseline suitable for engineering design and urban planning in the Baish district.