Lehmann discontinuity

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The Lehmann discontinuity, named after seismologist Inge Lehmann, is the discontinuity in seismic velocity near a depth of 220km, which is still debated. 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. The Lehmann discontinuity at one time referred to the inner core-outer core boundary, as Inge Lehmann discovered the inner core, but that usage is no longer current.

[edit] References

• http://geology.about.com/library/weekly/aa031598.htm
• http://www.physics.ucla.edu/~cwp/articles/bolt.html