Lehmann discontinuity
Encyclopedia
The Lehmann discontinuity refers to an abrupt increase of P-wave
and S-wave
velocities in the vicinity of 220±30 km depth, discovered by seismologist
Inge Lehmann
. It appears beneath continent
s, but not usually beneath ocean
s, 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.
P-wave
P-waves are a type of elastic wave, also called seismic waves, that can travel through gases , solids and liquids, including the Earth. P-waves are produced by earthquakes and recorded by seismographs...
and S-wave
S-wave
A type of seismic wave, the S-wave, secondary wave, or shear wave is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves....
velocities in the vicinity of 220±30 km depth, discovered by seismologist
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
Inge Lehmann
Inge Lehmann
Inge Lehmann FRS , was a Danish seismologist who, in 1936, argued that the Earth's core is not one single molten sphere, but that an inner core exists which has physical properties that are different from those of the outer core.-Life:Inge Lehmann was born and grew up in Østerbro, a part of...
. It appears beneath continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
s, but not usually beneath ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s, 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
S-wave
A type of seismic wave, the S-wave, secondary wave, or shear wave is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves....
anisotropy
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
. Further discussion of the Lehmann discontinuity is found in Kurato.