Abstract
We estimate the averaged 1‐D shear‐wave velocity of the upper mantle beneath western North America and the Kaapvaal region in southern Africa by inverting dispersion measurements of fundamental and higher Rayleigh modes recorded by ∼2000 km aperture broadband arrays. The overtones at periods exceeding 25 s constrain the averaged 1‐D shear‐wave velocity to 650 km depth across the regional arrays. Our overtone analysis confirms the shear‐wave velocity differences observed in global tomographic models with similar horizontal resolution: the western North American mantle features a prominent low velocity zone at depths 50–200 km, while the shear velocity in the upper 180–200 km of the mantle beneath southern Africa is at least 6% higher than in western North America which we interpret as the expression of a cratonic keel. There is no resolvable difference in shear‐wave velocity between southern Africa and western North America below a depth of about 300 km.
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