Lehmann discontinuity [SEP] named after
Lehmann discontinuity
The Lehmann discontinuity is an abrupt increase of "P"-wave and "S"-wave velocities at the depth of , discovered by seismologist Inge Lehmann. The thickness is 220 km. 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 asthenosphere, a phase transition, and most plausibly, depth variation in the shear wave anisotropy. Further discussion of the Lehmann discontinuity can be found in the book "Deformation of
in 1940, it was hypothesized that this inner core was made of solid iron. In 1952, F. Birch published a detailed analysis of the available data and concluded that the inner core was probably crystalline iron.
The boundary between the inner and outer cores is sometimes called the "Lehmann discontinuity", although the name usually refers to another discontinuity. The name "Bullen" or "Lehmann-Bullen discontinuity", after K. Bullen has been proposed, but its use seems to be rare. The rigidity of the inner