Complex Deep Structure of the African Low‐Velocity Zone

Abstract

Abstract We use recently deployed seismological arrays in Africa to sample a 2D cross section through the mantle down to the core–mantle boundary (CMB). By making use of travel‐time residuals of S , ScS , and SKS phases, a new shear‐velocity model of the African low‐velocity zone (ALVZ) is derived. Our model suggests between 1.2% shear‐velocity reduction at the top and 5% at the bottom with respect to 1D reference models. The average reduction over the whole low‐velocity zone (LVZ) amounts to 2% in the presented model and is therefore about twice as strong as values found in global tomographic models. The top of the LVZ reaches up to 1200‐km depth, and its lateral extent at the CMB is about 35°. We propose the existence of a gap of 300 km, splitting the structure into two blocks. Our results are based on remarkable differences in SK ( K ) S travel‐time residuals over a few degrees distance. The complexity of the structure could provide a key to an improved understanding of the deep‐mantle LVZ dynamics and composition by comparison to geodynamic models. The gap in the model might suggest that the 2D cross section is cutting through a 3D indentation in the boundary of the ALVZ but may also be interpreted as a sign of two individual plumes, rather than one large homogeneous upwelling. Electronic Supplement: Figures of preprocessed original waveforms aligned with the synthetics for the corresponding event, and tables of applied corrections.