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Science 23 October 1998:
Vol. 282. no. 5389, p. 589
DOI: 10.1126/science.282.5389.589b
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This Week in Science
Some mixing occurs between the iron-rich liquid outer core and the silicate-rich solid lower mantle in the 1000-kilometer region (called the D" region) above the core-mantle boundary (CMB), but it has been difficult to distinguish whether the D" region is a distinctive layer or just isolated regions of anomalous material. Bréger and Romanowicz (p. 718) measured the differences in travel times of different seismic shear waves through the D" region below the central Pacific Ocean. They then perturbed the velocity structure in a model of the D" region to account for the experimental data. Their refined model shows a slow velocity zone associated with the Hawaiian hot spot plume source at the CMB and a fast velocity zone associated with chemical heterogeneity, which indicates that the D" region is not a well-defined layer but is heterogeneous.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
