Focal mechanisms and the stress regime in NE and SW Tanzania, East Africa

Abstract

[1] We report 12 new focal mechanisms from earthquakes in NE and SW Tanzania where the stress regime within the East African rift system is not well constrained. Focal mechanisms for events at the intersection of the Lake Tanganyika and Rukwa rifts in SW Tanzania indicate a complicated stress pattern with possible dextral strike-slip motion on some faults but oblique motion on others (either sinistral on NW striking faults or dextral on NE striking faults). Within the Rukwa rift, focal mechanisms indicate normal dip-slip motion with NE-SW opening. In NE Tanzania where the Eastern rift impinges on the margin of the Tanzania Craton, fault motions are consistent with a zone of distributed block faults and sub E-W extension. All twelve earthquakes likely nucleated within the crust.

Spectral P-wave magnitudes, magnitude spectra and other source parameters for the 1990 southern Sudan and the 2005 Lake Tanganyika earthquakes

“…It is also agree with the predominant extension direction observed in the northern basin of the lake between 7.4 and 1.1 Ma (Lezzar et al, 1996). The focal mechanism solutions for the Rukwa Rift earthquakes indicate normal dip slip motion with a horizontal tension axis striking NE-SW (Zho et al, 1997;Brazier et al, 2005b). The fault planes are consistent with the orientation of the faults bounding the rift.…”

“…Field based geophysical investigation of the early Tertiary in Rukwa Basin identified a principle stress direction which agrees well with that derived from the focal mechanism solutions . At the intersection of the Lake Tanganyika and the Rukwa Rifts, the focal mechanisms show a complicated pattern with possible dextral strike slip motion but oblique motion on others (Brazier et al, 2005b).…”

Contrasted seismogenic and rheological behaviours from shallow and deep earthquake sequences in the North Tanzanian Divergence, East Africa

“…8). Deep crustal earthquakes have already been evidenced (Shudofsky et al, 1987;Seno and Saito, 1994;Foster and Jackson, 1998;Brazier et al, 2005), but more as isolated cases while it concerns here the majority of the events.…”

Fault kinematics and tectonic stress in the seismically active Manyara–Dodoma Rift segment in Central Tanzania – Implications for the East African Rift

“…From the North Tanzanian Divergence to Dodoma, only 12 earthquake focal mechanisms are available. They come from different sources: seven from the Harvard Centroid Moment Tensor catalogue, two from Kebede and Kulhanek (1991) and four from smaller earthquakes recorded by the Tanzania Broadband Seismic Experiment (Brazier et al, 2005). Two different solutions of the same event (i.e., December 15, 1977) are included in the database used in stress inversion (one from the Harvard catalogue and one from Kebede and Kulhanek, 1991) as it was not possible to determine a priori the solution to be favoured (Table 2a).…”