An updated Probabilistic Seismic Hazard Analysis (PSHA) for Sudan and South Sudan

Abstract

This paper aims to comprehensively update seismic hazard assessments for Sudan and South Sudan using the Probabilistic Seismic Hazard Analysis (PSHA) method. To achieve this goal, a new and up-to-date earthquake database was developed, which includes a newly unified and updated declustered catalog, earthquake sources, and focal mechanism database. Different magnitudes were homogenized to the moment magnitude (Mw) using region-specific conversion relationships based on orthogonal regression. In addition, two types of seismotectonic idealization were considered in the seismicity assessment: the area source model and the linear (fault) source model. Focal mechanisms were used to refine the stress regime for seismicity sources derived from formal inversion analysis. To handle uncertainty, the logic-tree framework is employed, with three different Ground Motion Prediction Equations (GMPEs). The results are obtained in terms of the PGA and for the first time the spectral accelerations at two vibration periods of 0.1 s and 1 s for 475 and 975 years return periods, respectively. Hazard curves and Uniform Hazard Spectra were obtained for three considerably vulnerable cities, and PSHA disaggregation was performed in the highest risk regions with nearby seismic sources. The highest PGA values were 0.195 g and 0.285 g, with a 10% and 2% chance of exceeding these values in 50 years, respectively, in South Sudan along the western branch of the East African Rift System (EARS). In view of the increase in population and infrastructure development in the region, these results will be invaluable for seismic safety and design.