A Bayesian probabilistic seismic hazard assessment for the Baish Dam, Southwestern Saudi Arabia

This study presents a Bayesian smoothed-seismicity probabilistic seismic hazard assessment (PSHA) for Baish Dam and the surrounding Wadi Baish area, southwestern Saudi Arabia. The workflow combines catalogue preparation, Gardner-Knopoff declustering, kernel-smoothed spatial seismicity modelling, Bayesian posterior sampling of source-node and recurrence parameters, GMPE logic-tree treatment, hazard-curve integration, uniform hazard spectrum calculation, and magnitude-distance/spatial deaggregation. The approach is used as a reproducible catalogue-based baseline because the local active-fault slip rates, segmentation, paleoseismic history, and recurrence parameters required for a complete fault-source model are not yet sufficiently constrained. The results show that the dam is mainly influenced by distributed seismicity along the southern Red Sea, Jizan-Yemen Hot Spot, southwestern Arabian-Yemeni, and Gulf of Aden-Afar domains. Mean rock-site PGA values are approximately 0.040 g and 0.069 g for the 475-year and 2475-year return periods, respectively, while SA(0.1 s) reaches about 0.096 g and 0.170 g. Deaggregation indicates that Mw 5.1–5.9 earthquakes at about 225-325 km dominate the catalogue-based hazard. These rock-site estimates provide a baseline for dam-safety evaluation, while future work should integrate active-fault characterization, site-response analysis, reservoir-foundation interaction, and fragility assessment to translate the probabilistic ground-motion levels into engineering risk metrics.