Lehmann_discontinuity

Lehmann discontinuity

Lehmann discontinuity

Lehmann discontinuity is a layer separating outer core from inner core.

This article is about a discontinuity in Earth's mantle. For the discontinuity in the core, see Earth's inner core.

The Lehmann discontinuity is an abrupt increase of P-wave and S-wave velocities at the depth of 220 km (140 mi) in Earth's mantle, discovered by seismologist Inge Lehmann.[2][3][4] The thickness is 220 km [citation needed]. It appears beneath continents, but not usually beneath oceans,[5] and does not readily appear in globally averaged studies. Several explanations have been proposed: a lower limit to the pliable asthenosphere, a phase transition,[6] and most plausibly, depth variation in the shear wave anisotropy.[7]

Velocity of seismic S-waves in the Earth near the surface in three tectonic provinces: TNA = Tectonic North America, SNA = Shield North America and ATL = North Atlantic.[1]

Notes

  1. [1]
    Figure patterned after Don L Anderson (2007). New Theory of the Earth (2nd ed.). Cambridge University Press. p. 102, Figure 8.6. ISBN 978-0-521-84959-3.; Original figure attributed to Grand and Helmberger (1984)
  2. [2]
    William Lowrie (1997). Fundamentals of geophysics. Cambridge University Press. p. 158. ISBN 0-521-46728-4.
  3. [3]
    Lehmann, I. (1936): P', Publications du Bureau Central Seismologique International, Série A, Travaux Scientifique, 14, 87–115.
  4. [4]
    Martina Kölbl-Ebert (December 2001). "Inge Lehmann's paper: " P' " (1936)" (PDF).
  5. [5]
    Lars Stixrude and Carolina Lithgow-Bertolloni (2005). "Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone". J. Geophys. Res. 110 (B3): B03204. Bibcode:2005JGRB..110.3204S. doi:10.1029/2004JB002965. hdl:2027.42/94924. 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.
  6. [6]
    Kent C. Condie (1997). Plate tectonics and crustal evolution (4th ed.). Butterworth-Heinemann. p. 123. ISBN 0-7506-3386-7.
  7. [7]
    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 1-86239-159-9.

General references

Further reading

Shun-ichirō Karato (2008). Deformation of earth materials: an introduction to the rheology of solid earth. Cambridge University Press. p. 318. ISBN 978-0-521-84404-8.


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