# Preliminary Seismic Hazard Analyses for the Ugandan Region
###### Abstract  
Uganda is situated between the two seismically active branches of the East African Rift Valley System, which are characterized by high levels of seismicity. A probabilistic approach has been used to assess the seismic hazard for Uganda and the surrounding areas. A probabilistic seismic hazard analysis requires the availability of an earthquake catalog, relevant ground motion prediction equations, and an outline of how the hazard calculations will be conducted. Using online sources, an earthquake catalog for Uganda and the immediate areas around Uganda was compiled spanning 108 years, from 1912 to 2020. This catalog was homogenized to moment magnitude to match with the selected ground motion prediction equations from Toro and Idrisis. A logic tree accounting for the two ground motion prediction equations and dividing the study region into four seismic zones was used for calculating the seismic hazard. As an example, the seismic hazard results at two sites close to each other showed how different seismic hazards can be. Results from the probabilistic seismic hazard analyses was expressed through seismic hazard maps for peak ground acceleration at 10% probability of exceedance in 5, 10, 20, 50, 100 and 500 years, corresponding to return periods of 50, 100, 200, 500, 1000 and 5000 years, respectively. The seismic hazard map for 10% probability of exceedance in 5 years calculated PGAs from 0.02 to 0.10 g and 0.10 to 0.27 g outside of and within the western branch of the East African Rift Valley System, respectively. The estimated PGAs from previous studies at a similar probability of exceedance level are within the range of these findings, although the ranges calculated herein are wider. e 2022125981202222125981  
and the East African Rift branch which runs from lake Turkana in the north to Lake Eyasi in the south. Being situated between the western and eastern branches of the East African Rift System, the seismicity and structural geology in the country is dominated by the tectonics associated with this East African Rift Valley System. Geological shear zones happen in the Precambrian rocks in numerous regions of the country. The Aswa shear zone is the greatest widespread and follows a northwesterly inclination for over 300 km via north Uganda and into South Sudan. Additional shear zones run through Karamoja, Acholi, and the West Nile regions. The country also has extinct volcanic mountains mainly situated along the eastern, northern, and southwestern borders. On the edge with Kenya is noticeable by volcanic mounts, dominated by Mount Elgon, an extinct volcano, with elevations glowing 30 km from its crater. This mountain is characterized by rich soils of weak stability at its slopes and this has made the area prone to landslides. North of Mount Elgon are more extinct volcanoes such as Mount Kadam, Mount Zulia, Mount Morungole, and the Labwor and Dodoth Hills. On the border with South Sudan are Imatong Mountains and Mount Langia, all of volcanic origin. In the southwest, there are the extinct volcanos of Mount Mahavura, Mount Mgahinga, and Mount Sabinio of the Mufumbira mountain range, which notes the edge with Rwanda and Democratic Republic of Congo. These extinct volcanoes have rich soils of weak stability and have been prone to landslides, especially seismically induced landslides. In modern times, a number of destructive earthquakes caused loss of life, damage to properties, and many other calamities in Uganda. All these disasters have been reported in this century with examples provided in Table 1. Characterization of the seismotectonic behavior of the region is still lacking. Several teams have conducted earthquake-related studies for hydroelectric projects, industrial development, urbanization, and resource exploration infrastructure [1; 2; 3; 4; 5; 6]. Most of these studies were conducted for specific regions like the Albertine graben and other minority projects. Such losses from earthquakes are significant to a community and a mitigation strategy is to characterize these seismic hazards.