Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics

Abstract

Source parameters for 38 African earthquakes have been determined using P and SH body-waveform inversion of analogue and digital waveforms. The results of this modelling are combined with 15 other earthquakes whose source parameters are also well constrained by body-waveform inversion. This data set shows that parts of East Africa have a seismogenic thickness of up to ∼ 35km, and that seismicity occurs throughout the upper and lower crust. 1-D heat-flow calculations suggest temperatures of ∼ 325–475° C at 35km depth in the Archaean and Proterozoic crust, requiring that the lower crust has a dry, mafic bulk composition in order to deform seismogenically. The slip vectors associated with these 53 earthquakes are combined with an additional 28 solutions from the Harvard CMT catalogue in order to investigate plate kinematics. In the Red Sea/Gulf of Aqaba the slip vectors agree closely with the Africa–Arabia extension direction predicted by the current best-fit plate model of Jestin, Huchon & Gaulier (1994). In the southern East African Rift System motion is split between a southeast direction in Zambia and a northeast direction in Malaŵi and Rukwa, which combine to achieve the predicted Africa–Somalia east–west extension. Thus the current best-fit plate model of Jestin . (1994) adequately describes the active kinematics of Africa.