Earth’s Structure, Upper Mantle
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The upper mantle is defined as that part of the mantle between the crust and the phase transition of γ–olivine to perovskite. The total mass of the upper mantle is 1.06 × 1024 kg, about a quarter of the total mass of the mantle. Its volume, 2.95 × 1011 km3, is a third of the total volume of the mantle.
Until the discovery of a major transition near 660-km depth, the upper mantle was better known as Bullen’s “layer B,” extending to 400-km depth. A sharp gradient or discontinuity in seismic velocity causes a bend in the travel time curves of P-wave arrivals near 20°, such that the slowness drops from more than 12 s/deg. to 10 s/deg. This phenomenon was observed as early as 1931 by Jeffreys, who correctly adopted a suggestion by J.D. Bernal that it represents a high-pressure modification of olivine. The modern notion of the upper mantle actually extends into Bullen’s next layer, “layer C,” which has now been abandoned as a physically meaningful subdivision.
The depths to the...
- Bostock M (2009) Teleseismic body-wave scattering and receiver-side structure. In: Romanowicz B, Dziewonski A (eds) Seismology and structure of the Earth. Elsevier, Amsterdam, pp 219–246Google Scholar
- Jordan T (1981) Continents as a chemical boundary layer. Philos Trans R Soc Lond 301A:359–373Google Scholar