Surface wave tomography: Imaging of the lithosphere–asthenosphere boundary beneath central and southern Africa?

Volcanism in the Afar Rift sustained by decompression melting with minimal plume influence

“…The depth of the large negative phase beneath the rift flank is coincident with the base of the seismically fast lid from surface waves and body waves, ∼50-80 km beneath the flank regions, and is therefore the lithosphere-asthenosphere boundary 12,18 (LAB), in agreement with previous single-station receiver-function results (see Supplementary Information). The lack of a strong negative LAB phase beneath the rift indicates that the mantle lithosphere has been replaced by upwelling asthenosphere.…”

“…The lack of a strong negative LAB phase beneath the rift indicates that the mantle lithosphere has been replaced by upwelling asthenosphere. This is supported by previously reported seismic-velocity models that lack a velocity inversion beneath the rift 12,18 . Indeed, plate-reconstruction models require the lid to be stretched by factors of three and two beneath Afar and the MER, respectively 19 , which is roughly explained by the absence of subcrustal lithosphere beneath the rift 7 .…”

“…One per cent melt retention assumes strong melt-buoyancy effects, which have been previously proposed for mid-ocean ridges 21 and are also probably required beneath Afar. Previous surface-wave, body-wave and receiver-function results have similarly interpreted very slow velocities and very high V p /V s values as significant amounts of shallow melting 9,11,12 .…”

“…Several recent seismic studies found evidence for melt in the crust and upper mantle beneath the rift based on high ratios of the P-wave velocity to the S-wave velocity (V p /V s ratios), velocities 5-10% slower than the global average and anisotropy [9][10][11][12][13] . However, precise determination of lithospheric thickness and depth of melting have proved challenging with existing seismic methodologies.…”

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

“…Scholz & Rosendahl 1988;Specht & Rosendahl 1989), and regional to continental studies of the entire EARS (e.g. Weeraratne et al 2003;Pasyanos & Nyblade 2007;Fishwick 2010). Recent regional-scale studies using surface and body waves image a circular low-velocity region centred on the RVP within the uppermost mantle, which weakens and becomes more diffuse at greater depths (∼140 km; Adams et al 2012;O'Donnell et al 2013).…”