Probabilistic Earthquake Risk Assessment Framework for Uganda: Event-Based Modelling Approach

Abstract

Uganda’s geology, tectonics and morphology exposes most of its territory to earthquakes of low to moderate intensities. Past earthquakes such as the 1966 Toro, 1994 Kisomoro and 2016 Bukoba events have had detrimental consequences on the socio-economic welfare and resilience of communities across Uganda. Despite earlier efforts in predicting seismic hazard in Uganda, there is no comprehensive study published on earthquake-related risks across the country. Whilst losses during the previous earthquakes were still compar-atively low, damage due to future earthquakes are likely to escalate considerably because of the proliferation of a largely substandard building stock coupled with rapid population growth and urbanisation. As a first step towards building an earthquake risk and resilience framework for Uganda, this work employs the probabilistic event-based risk calculator of OpenQuake-engine to holistically assess potential losses resulting from future earthquakes. Using a fault-oriented spatially distributed seismicity approach, a logic tree is implemented to minimise the associated epistemic uncertainties and site conditions are modelled using the shear wave velocity in the upper 30m of soil across Uganda. The building stock is largely inferred and projected from the 2014 national population and housing census and analytical vulnerability curves are selected from the GEM global database. The analysis of earthquake ruptures, hazard maps, loss exceedance curves, mean annual loss maps and aggregated asset loss statistics indicate that western Uganda is prone to the highest risk. These findings will be a huge step towards the urgent need to update the Uganda Seismic Design Code, strategically plan land use patterns, optimise earthquake insurance pricing and improve the National Policy for Disaster Preparedness and Management.