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| [[File:S-wave velocity.PNG|250px|thumb|Velocity of seismic ''S''-waves in the Earth near the surface in three tectonic provinces: TNA= Tectonic North America SNA= Shield North America & ATL = North Atlantic.<ref name=Anderson1> | |||
| Figure patterned after {{cite book |title=New theory of the earth |author=Don L Henderson |url=http://books.google.com/books?id=KB3KsIPa94sC&pg=PA102 |page=102, Figure 8.6 |isbn=0521849594 |year=2007 |edition=2nd |publisher=Cambridge University Press}}; Original figure attributed to Grand & Helmberger (1984) | |||
| </ref>]] | |||
| The '''Lehmann discontinuity''', originally referred to the liquid-solid boundary between the outer and inner core of the Earth in honor of ] ], who proposed on the basis of seismic waves that the Earth had an inner core. <ref name=Krebs> | The '''Lehmann discontinuity''', originally referred to the liquid-solid boundary between the outer and inner core of the Earth in honor of ] ], who proposed on the basis of seismic waves that the Earth had an inner core. <ref name=Krebs> | ||
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The Lehmann discontinuity, originally referred to the liquid-solid boundary between the outer and inner core of the Earth in honor of seismologist Inge Lehmann, who proposed on the basis of seismic waves that the Earth had an inner core. Later (1940) it was conjectured that this inner core was solid iron, and its rigidity was confirmed in 1971.
However, today the Lehmann discontinuity refers to an abrupt increase of P-wave and S-wave velocities in the vicinity of 220±30 km depth, as also was discovered by Lehmann. It appears beneath continents, but not usually beneath oceans, and does not readily appear in globally-averaged studies. Several explanations have been proposed; a lower limit to the pliable aesthenosphere, a phase change, and most plausibly, depth-variation in the shear wave anisotropy. Further discussion of the Lehmann discontinuity is found in Kurato and Kurato.
Notes
- Figure patterned after Don L Henderson (2007). New theory of the earth (2nd ed.). Cambridge University Press. p. 102, Figure 8.6. ISBN 0521849594.; Original figure attributed to Grand & Helmberger (1984)
- This usage still can be found: see for example: Robert E Krebs (2003). The basics of earth science. Greenwood Publishing Company. ISBN 0313319308.
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William Hung Kan Lee (2002). International handbook of earthquake and engineering seismology; volume 1. p. 926. ISBN 0124406521.
{{cite book}}: Unknown parameter|publihser=ignored (|publisher=suggested) (help) - William Lowrie (1997). Fundamentals of geophysics. Cambridge University Press. p. 158. ISBN 0521467284.
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Lars Stixrude and Carolina Lithgow-Bertolloni (2005). "Mineralogy and elasticity of the oceanic upper mantel: Origin of the low-velocity zone" (PDF). J Geophys. Res. 110: B03204. doi:10.1029/2004JB002965.
The first possible explanation is that the Lehmann is not a global feature...the Lehmann is more prevalent under continents and may be absent under all or most of the oceans.
- Kent C. Condie (1997). Plate tectonics and crustal evolution (4rth ed.). Butterworth-Heinemann. p. 123. ISBN 0750633867.
- MK Savage, KM Fischer CE Hall (2004). "Strain modelling, seismic anisotropy and coupling at strike-slip boundaries...". In John Gocott (ed.). Vertical coupling and decoupling in the lithosphere; Volume 227 of special publications. Geological Society. p. 14. ISBN 1862391599.
- Shun-ichiro Karato, Shunʼichirō Karato (2008). Deformation of earth materials: an introduction to the rheology of solid earth. Cambridge University Press. p. 318. ISBN 0521844045.
General references
- P Caloi (1967). "The "20° Discontinuity"". In H. E. Landsberg, J. Van Mieghem (ed.). Advances in geophysics, Volume 12. Academic Press. p. 167 ff. ISBN 0120188120. – some historic background.
See also
External links
- From here to "hell," or the D layer, About.com
- Inge Lehmann, UCLA
- Career highlights of Inge Lehmann from UCLA
| Structure of Earth | |
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| Shells | |
| Global discontinuities | |
| Regional discontinuities | |
