DEVELOPMENT OF A PROBABILISTIC SEISMIC RISK ASSESSMENT FRAMEWORK FOR CRITICAL INFRASTRUCTURE IN WEST AFRICA (PSRA CIWA)

Abstract

Dams are essential infrastructures for human activities and the economic development of a region. Therefore, dam safety is a priority, particularly regarding natural events like earthquakes. Furthermore, since past seismic activities revealed damage to dams and their host environments, it is required to perform a seismic risk assessment to identify the criticalities and prevent damage consequences. The research illustrates a probabilistic framework for seismic risk assessment of critical infrastructure in West Africa for such reasons. West Africa is a stable continental with a few reported earthquake magnitudes greater than 5, mainly the 1939 Mw 6.4 Accra (Ghana) and 1983 Mw 6.3 Northwest Guinea earthquakes. Earlier studies tried to assess the region's seismic hazard but only focused on the narrow area close to the Gulf of Guinea. Their assessments produced seismic hazard maps for a 475-year, but the current study examined a wider area based on updated earthquake catalogue of West Africa with higher return periods. Deaggregation was also introduced to identify the dominant earthquake scenario for Accra. It was observed that the prevalent scenario is dominated by seismic events between magnitudes 5.5-6.0 and at a distance less than 60 km. However, despite the encouraging results from earlier hazard assessments, it was limited to old-outdated ground motion prediction equations (GMPEs). Also, the seismic hazard assessments (SHA) obtained was only for a 475-year return period; thereby, the outcome can only be used for building code. Consequently, a probabilistic seismic hazard assessment (PSHA) was developed using R-CRISIS software to build seismic codes for the region and critical infrastructures such as large dams, lifelines, and power plants. Assessing the potential seismic risk for large dams across the region of West Africa was done to determine the dams' most vulnerable based on the method proposed by Bureau (2003). The assessed dams are based on the seismicity within the dam sites and their physical properties and locations risks. The development of the Bureau (2003) method requires different factors and weighing points of the types of dams, age, reservoir capacity, downstream risk potential, and vulnerability. Hence, this was achieved by combining the probabilistic seismic hazard assessment (PSHA) at the dam sites and the risk rating of the dam structures to estimate the total risk factor (TRF) of the dams. A non-linear time history recorded data was used to implement non-linear numerical procedures to estimate the region's most critical dam (Akosombo dam) behaviour. Nineteen real accelerograms were obtained from the Pacific Earthquake Engineering Research Center (PEER) ground motion website and European strong-motion (ESM) database and processed by SeismoSignal. In addition, PLAXIS 2D is used for numerical analysis. As a result, dynamic deformations and factors of safety were obtained for the dam.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ahmad Syed Mohd Syed (Supervisor) & Domenico Lombardi (Supervisor)