Seismological mapping of fine structure near the base of the Earth's mantle

J.E. Vidale; H.M. Benz

doi:10.1038/361529a0

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Seismological mapping of fine structure near the base of the Earth's mantle

J.E. Vidale·H.M. Benz

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Abstract

The Earth's core–mantle boundary (CMB) juxtaposes liquid iron and crystalline silicates, and is a region of large vertical thermal gradients. The D" region, which extends up to 200–300 km above the CMB, often has elevated shear-wave velocity and suggestions of lateral variations in structure 1 . Recent improvements in our ability to assemble and analyse records from regional seismic networks have allowed us to examine long profiles of travel times, amplitudes and waveforms from more than a thousand short-period seismometers 2 . We observe, across Canada and the United States, P waves that have grazed the CMB from the powerful nuclear test in Lop Nor, China, on 21 May 1992. First-arrival travel times and large secondary arrivals are consistent with a 1.5% compressional velocity increase with depth ∼ 130 km above the CMB—about half the thickness of D" in this locality 3 . Our observations, together with evidence for the absence of such a thin, fast layer in neighbouring regions, suggest the presence of lateral heterogeneity in composition or phase at the base of the mantle.

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J.E. Vidale, H.M. Benz. 1993. Seismological mapping of fine structure near the base of the Earth's mantle. https://doi.org/10.1038/361529a0

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