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

Abstract

a b s t r a c tSeismicity patterns 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 (~75%) extends to the south of the Manyara segment along the eastern margin of the Tanzania Craton, and at~6-7°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 (~25%) is found extending from the SE corner of the Tanzania Craton at~6-7°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.

Lithospheric modification by extension and magmatism at the craton-orogenic boundary: North Tanzania Divergence, East Africa

“…Our results demonstrate a broadening of this anomaly. The Pangani Branch, of Resolution matrix diagonal term the NTD, is associated to an asthenospheric anomaly of small extent, which can explain the limited amount of magmatism and faulting in this zone (Mulibo & Nyblade 2016;Weinstein et al 2017). Synthetic tests indicate that the best lateral resolution of our models is between 50 and 200 km, including negative bodies (Figs S1 and S2).…”

Variations in the Seismogenic Thickness of East Africa

“…Temporary local networks of seismometers, allowing the detection and location of smaller‐magnitude earthquakes, have been operating across East Africa since the early 1990s, although, due to the logistical requirements, they remain sparse. We compile the results from 13 high‐quality seismic surveys, covering regions including Afar and the Main Ethiopian Rift (Illsey‐Kemp et al., 2018; Keir et al., 2006), the Eastern Branch through Kenya and Tanzania (Ibs‐von Seht et al., 2001; Langston et al., 1998; Mulibo & Nyblade, 2016; Weinstein et al., 2017; Young et al., 1991), and the Western Branch from Lake Albert (Lindenfeld et al., 2012a; F. A. Tugume & Nyblade, 2009), through Tanganyika (Lavayssière et al., 2019) and Rukwa (Camelbeeck & Iranga, 1996), to northern Malawi (Ebinger et al., 2019; Gaherty et al., 2019): all shown on Figure 3.…”

Thermochemical Modification of the Upper Mantle Beneath the Northern Malawi Rift Constrained From Shear Velocity Imaging

“…Taken together, these factors suggest thermo-chemical modification of the northeastern flank. Such modification may be enhanced here due to the proximity to the RVP or related to its location within the region of diffuse deformation between the Eastern and Western Rifts (e.g., Adams et al, 2018;Mulibo and Nyblade, 2016).…”