Present-day Fault Kinematics and their Reactivation Likelihood within and South of the North Tanzania Divergence (NTD), East African Rift System: Implication for Geo-hazards Assessment

Abstract

Abstract This study investigates the relationship between the North Tanzania Divergence (NTD), the southern part of the NTD and the rift structures in the eastern part of the East African Rift System (EARS). It also assesses the susceptibility of these structures to reactivation under the current stress field. Fault slip data and focal mechanisms from various sources have been used to determine the minimum horizontal stress axes (Shmin) of different faults, including the Eyasi rift border fault south of the NTD. The analysis reveals that faults trending NW-SE to NNW-SSE have a sinistral sense of movement, while those trending NE-SW generally have a dextral sense of movement. The N60°E trending faults that dip easterly are not optimally oriented with the current stress field and have a low to moderate likelihood of reactivation. This includes the NE-SW trending Eyasi rift border fault (part of the NTD) and other structures oriented N60°E south of the NTD, with a computed slip tendency (Ts) of less than 0.5. Faults trending N-S, NNW-SSE, and NNE-SSW, on the other hand, have a high to the highest likelihood of reactivation (Ts > 0.85). The other faults in the study area, which trend NE-SW or NW-SE, have Ts values expressed as 0.5 ≤ Ts < 0.85. These findings have important implications for earthquake risk assessment in the NTD and south of the NTD, as geological constraints need to be taken into account for better management and mitigation. The results could be applied elsewhere in the EARS provided that they are under E-W extensional stress regime.