SEISMIC HAZARD ANALYSIS FOR THE ALBERTINE REGION, UGANDA - A PROBABILISTIC APPROACH

The Albertine region of Uganda is characterized by high levels of seismic activity and by many active normal faults. The aim of this work is to assess the potential hazard accruing from earthquakes in the Albertine region, using the probabilistic approach to assess the seismic hazard for, specifically, the Hoima and Buliisa districts. The input parameters for the seismic hazard computation were obtained using the earthquake catalogue compiled for the period 1900 to 2012, including earthquakes within an area bounded by latitudes 1.5 degrees S to 4 degrees N and longitudes 29 degrees E to 33 degrees E. All magnitudes were homogenized to moment magnitude scale. The study area was divided into two seismic source zones based on seismotectonic analysis. The updated ground motion prediction equation by Pankow and Pechmann was used in the computations. Seismic hazard maps in terms of the Peak Ground Acceleration (PGA) for 10%, 5% and 2% probabilities of exceedance in 50 years were derived. The results show that the PGA values for both districts fall in the range of 0.152 to 0.162 g, 0.187 to 0.195 g and 0.248 to 0.256 g (where g is the acceleration due to gravity), for return periods of 475, 975 and 2,475 years, respectively. The highest levels of seismic hazard were found in the southwestern part of the Hoima district, where PGA values were in excess of 0.162 g, 0.195 g and 0.256 g for 10%, 5% and 2% chances of exceedance in 50 years, respectively. We conclude that in the Albertine region, the return period for an earthquake capable of causing damage to engineering structures is, on average, 30 years. It is thus recommended that all important engineering structures in the region should be designed for earthquake resistance.