Morphostructural analysis of the Eyasi–Durumo-Manyara-faults, East African Rift System

ABSTRACT The Eyasi, Durumo, Manyara, and Eyasi antithetic faults, located about 250 km west of Dodoma, Tanzania, are part of the East African Rift System (EARS) and re-activate the Archean rocks of the Tanzania Craton. The Durumo fault trends N-S, while the others trend NE-SW. Among these, the Eyasi fault, a border fault of the Eyasi basin, is considered a potential reservoir for petroleum and helium, which motivated this study. We analyzed 64 profiles using 30 m-resolution SRTM data, spaced approximately 5 km apart, to extract X-Y coordinates and elevation (Z) for each point. This data was used to calculate morphostructural parameters such as vertical offsets (Vo), maximum slope angles (Smax), and slope differences (Sdiff), which help estimate fault segments and model fault propagation styles (restricted or unrestricted). Our results indicate that fault vertical offsets (Vo) are proportional to maximum slope angles (Smax) for scarps with Vo ≤ 0.85 km, with a constant of proportionality K = 15 m/degree. This suggests that K = 15 m/degree is most effective for smaller fault scarps with vertical offsets much less than 1000 m. We also found that slope differences (Sdiff) can reach up to 60° in areas where fault steps intersect. Additionally, our analysis shows that fault tip propagation is hindered to the northeast, but the faults propagate more easily to the southwest. This southward propagation through the Archean Tanzania Craton indicates that the Craton has little to no effect on the faults’ southward movement, suggesting that these faults can re-activate and potentially cause large earthquakes. Finally, we demonstrate that using vertical offsets(Vos) computed from fault steps provides a clearer contrast and better characterization of fault displacement profiles compared to profiles based on cumulative or combined vertical offsets.