Although the Earth is a complex body with pervasive three‐dimensional structure in its solid portions, the dominant variation in properties is with depth. The figure of the Earth is close to an oblate spheroid with a flattening of 0.003356. The radius to the pole is 6357 km and the equatorial radius is 6378 km; for most purposes, a spherical model of the Earth with a mean radius of 6371 km is adequate. Thus, reference models for internal structure can be used in which the physical properties depend on radius. Three‐dimensional variations can then be described by deviations from a suitable reference model.
The main divisions of Earth structure are illustrated in Figure E1. Beneath the thin crustal shell lies the silicate mantle which extends to a depth of 2890 km. The mantle is separated from the metallic core by a major change of seismic properties that has a profound effect on global seismic wave propagation (see Seismic phases ). The outer core behaves as a fluid at seismic...
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Kennett, B. (2007). Earth Structure, Major Divisions. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_85
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