Seismological investigations of lithospheric structure beneath the East African Rift System and the Kalahari Craton

In spite of numerous geophysical studies have been conducted in East African Rift System and Southern Africa, the structure and evolution of the crust and upper mantle are still controversial. In this study, we applied multiple seismological techniques to investigate the structure in the crust and uppermost mantle beneath the East African Rift System and Kalahari Craton in southern Africa. First, the technique of ambient noise tomography was applied to image shear wave velocity model from surface to the depth of 40 km beneath the Malawi and Luangwa rift zones. For the first time, a high-resolution 3-D shear wave velocity model was constructed in this region. Crustal thinning of several kilometers was inferred beneath the two rift zones. The existence of a high velocity anomaly in the mid crust beneath the Malawi Rift Zone could be best explained by the higher-than-normal temperature as well as partial melt. Next, we utilized a non-linear Bayesian Monte-Carlo joint inversion of surface wave dispersion and receiver functions to investigate the lithospheric structure and evolution of the Kalahari Craton for the second project. A well-constrained 3-D shear wave velocity model was obtained from surface to the depth of 100 km. The Kalahari Craton has undergone several lithospheric modifications including basalt depletion, magmatic intrusion, and lithospheric refertilization. Finally, a crustal thickness-Vp/Vs stacking receiver function analysis was applied in the Ethiopian Plateau and adjacent areas in northeastern Africa. The measured crustal thickness and Vp/Vs values show clear spatial correspondence with the geological observations on surface. The anomalously high crustal Vp/Vs measurements suggest the pervasive existence of magmatic intrusion and partial melt in the study region --Abstract, page iv