Variable extension in Lake Tanganyika

Lake Tanganyika is part of the east African rift system. The amount of extension along 22 dip section seismic lines in the lake has been measured. The maximum extension observed is 4.5 km (approximately 10%) at the central part of the rift and decreases to about 0.5 to 1‐km extension at the north and south ends of the rift. Deformation style changes with the amount of calculated extension. More complex rift geometries (paired half grabens and full grabens) are found in the central part where extension is greatest while single half grabens are present toward the northern and southern ends of the lake where extension is less. Local decreases in the amount of extension are superimposed on this regional trend. These drops tend to occur in regions defined as transfer zones and suggest a change from simple extension to more complex three‐dimensional strains (extension in more than the dip direction). Implied in the relationship between rift morphology and observed extension is the conclusion that Lake Tanganyika is a single rift segment that did not propagate with time but grew as a fixed length segment from day 1. Lake Tanganyika is a subsidence‐dominated rift, with up to 7‐km vertical displacement along major boundary faults for only 4.5‐km extension. The fairly steep, weakly listric boundary faults indicate that they sole out at deep (20–30 km) crustal levels.