Mantle discontinuities beneath Southern Africa

Abstract

Seismic velocity discontinuities within the top 1000 km of the Earth beneath southern Africa are imaged by stacking about 1300 source‐normalized broadband seismograms recorded by the Southern African Seismic Experiment. The Moho, 410, and 660 kilometer discontinuities are clearly detected. The mean mantle transition zone thickness is 245 km, essentially the same as the global average, suggesting that the transition zone is not anomalously warm. Thus, the lower‐mantle ‘African Superplume’ beneath our study area has no discernible effect on transition zone temperature and is consequently confined to the lower mantle. Variations in transition zone thickness appear to be related to the presence or absence of thick lithosphere. We do not detect several previously‐reported discontinuities beneath continents, such as the Hales or Lehmann discontinuities, and find no evidence for a 520 km discontinuity, nor do we detect a previously proposed low‐velocity zone just above the transition zone.