Active compressional tectonics in central Africa and implications for plate tectonic models: evidence from fault mechanism studies of the 1998 earthquakes in the Congo Basin

Two earthquakes occurred in the Congo Basin in March and April 1998. These two events are reported to have comparable size (5.5 Mb) and nearly the same epicentral locations, far from the western branch of the East African Rift System (EARS). The P-wave groups of these two earthquakes as recorded at FURI station have nearly identical waveforms, which is indicative of similar rupture process. The epicentral distribution in the area has no apparent trend and the reported seismicity is relatively sporadic. The results of the fault mechanism study show that the two earthquakes have a similar rupture process with slight variation. The duration of the main shock (event 980426) is 3.3 s and its scalar seismic moment, M-o, is 2.6 x 10(17) Nm. The style of the dominant deformation for both events is thrust type, which is not commonly observed in the African Plate. A compressive stress environment may be created by plate-boundary forces of the mid Atlantic Ridge and the EARS. (C) 2002 Elsevier Science Ltd. All rights reserved.