The seismotectonics of Southeastern Tanzania: Implications for the propagation of the eastern branch of the East African Rift

摘要

Seismicity pattems and focal mechanisms in southeastern Tanzania, determined from data recorded on temporary and permanent AfricaArray seismic stations, have been used to investigate the propagation direction of the Eastern branch of the East African Rift System southward from the Northern Tanzania Divergence Zone (NTDZ). Within the NTDZ, the rift zone is defined by three segments, the Eyasi segment to the west, the Manyara segment in the middle, and the Pangani segment to the east Results show that most of the seismicity (similar to 75%) extends to the south of the Manyara segment along the eastern margin of the Tanzania Craton, and at similar to 6-7 degrees S latitude trends to the SE along the northern boundary of the Ruvuma microplate, connecting with a N-S zone of seismicity offshore southern Tanzania and Mozambique. A lesser amount of seismicity (similar to 25%) is found extending from the SE corner of the Tanzania Craton at similar to 6-7 degrees S latitude southwards towards Lake Nyasa. This finding supports a model of rift propagation via the Manyara segment to the southeast of the Tanzania Craton along the northern boundary of the Ruvuma microplate. However, given the limited duration of the seismic recordings used in this study, the possibility of another zone of extension developing to the south towards Lake Nyasa (Malawi) cannot be ruled out. Focal mechanisms along the boundary between the Victoria and the Ruvuma microplates and offshore southeastern Tanzania show a combination of normal and strike slip faulting indicating mainly extension with some sinistral motion, consistent with the mapped geologic faults and a clockwise rotation of the Ruvuma microplate. (C) 2016 Elsevier B.V. All rights reserved.