The Thickness of Tectonic Plates

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Science  24 Apr 2009:
Vol. 324, Issue 5926, pp. 474-476
DOI: 10.1126/science.1172879

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A fundamental premise of plate tectonics on Earth is that rigid lithospheric plates, formed at mid-ocean ridges, float above a more deformable substratum, the asthenosphere (1). The precise nature of the asthenosphere is still debated. Mechanical models predict a well-defined, sharp lithosphere-asthenosphere boundary (LAB), but evidence for such a boundary from conventional seismic measurements is ambiguous. On pages 499 and 495 of this issue, Kawakatsu et al. (2) and Rychert and Shearer (3) present analyses of more sophisticated seismic studies that help refine the LAB and hence the thickness of the lithosphere and tectonic plates, although challenges still remain in picking out this boundary versus other structures within the lithosphere.