Global shear velocity tomographic models show two large-scale low velocity structures, so-called superplumes, in the lower mantle, under Africa and under the mid-Pacific. Sharp lateral velocity changes have been documented for some parts at the borders of the superplumes (e.g.Wen, 2001, To et al., 2005, He et al., 2006). We evaluate the distribution and amplitude of the anomalies given by a tomographic model for the D'' layer around the Pacific region by measuring travel times of Sdiff, SKS and SKKS phases. We search for sharp lateral velocity changes, which have not been found yet, at the borders and also inside, according to tomographic models, the superplume.
Berkeley Seismological Laboratory
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