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

Nature

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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 structure1. 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 seismometers2. 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 locality3. 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.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Seismological mapping of fine structure near the base of the Earth's mantle
Series title:
Nature
Volume
361
Issue:
6412
Year Published:
1993
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Nature
First page:
529
Last page:
532