G Below Sea

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Science  14 Mar 2014:
Vol. 343, Issue 6176, pp. 1175
DOI: 10.1126/science.343.6176.1175-f

Rheological differences between Earth's lithosphere and asthenosphere help drive plate tectonics. Geophysical analyses repeatedly reveal a seismic Gutenberg (G) discontinuity at 40- to 100-kilometer depth in oceanic plates, although the origin of this boundary remains enigmatic. Beghein et al. (p. 1237, published online 27 February) found that vertical stratification of anisotropy aligned with the depths of the G discontinuity, but not with the lithosphere-asthenosphere boundary. It appears that the G discontinuity forms when there are geophysical changes in the mantle, such as dehydration beneath mid-ocean ridges.

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