The Rukwa Rift is a late Tertiary rift system superimposed on a earlier Karroo (age) rift. In both rift basins extension increases towards the southeast, and probably developed under oblique extension. The influence of Precambrian and Karroo structures on the Tertiary fault pattern is very important and imparts an overall northwest-south trend to the rift. The Lupa Fault on the northeastern margin of the basin dominates the structural style. In the southeastern area this fault is listric in cross section and accommodates about 10 km of Tertiary extension. Passing northwards, the fault decreases in extension to about 2 km, the Tertiary-Recent basin fill correspondingly decreases in thickness from 7 km to 2 km. There is evidence for marked switching of paleostress directions during Tertiary to Recent time—the present state of stress indicated by earthquakes is east northeast-west southwest to northeast-southwest. Two wells have been drilled in the basin and are important correlation points for seismic data. The late Miocene-Recent rocks/sediments in the Galula-1 and Ivuna-1 wells are dominantly sandy fluvio-deltaic deposits or shallow-water lacustrine shales. Axial drainage into a relatively short rift segment kept the sediment supply high, apparently not permitting the development of extensive deep-water lacustrine shales.