Seismic risk assessment of residential buildings in the Greater Accra Metropolitan Area using the OpenQuake Engine: 1939 earthquake scenario

Abstract

Ghana faces a range of natural hazards, but one of the most significant and under-prioritised is seismic risk, particularly in the Greater Accra Metropolitan Area (GAMA), a densely populated urban centre exposed to a substantial yet underappreciated earthquake threat. This study assesses the seismic risk of GAMA’s residential building stock to quantify the potential societal consequences of a major earthquake. Using the open-source OpenQuake Engine, an exposure model of residential buildings, classified by construction material and construction period, was integrated with deterministic seismic hazard scenarios based on the destructive 1939 Accra earthquake. Communities in coastal and western GAMA, characterised by soft soils that amplify ground shaking and a high concentration of vulnerable unreinforced masonry buildings, are identified as the most at risk. The analysis indicates that the current Ghana Building Code, when compared with ground-motion predictions from the Atkinson and Boore (2006, modified 2011; AB11) model, may significantly underestimate seismic input in these vulnerable areas, potentially leaving communities exposed to higher levels of risk. In contrast, the Pezeshk et al. (2011; PE11) ground-motion model produces estimates that are broadly consistent with the Ghana Building Code. The results translate into tangible societal impacts: widespread building damage and collapse in high-risk neighbourhoods could result in mass casualties, large-scale displacement, and long-term socioeconomic disruption. This research provides a robust evidence base for decision-makers, underscoring the urgent need for targeted risk-reduction strategies. We conclude that enhancing Accra’s earthquake resilience requires strengthened enforcement of building codes and the implementation of targeted retrofitting programmes in the most vulnerable communities to safeguard lives and livelihoods.