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The Lehmann discontinuity is an abrupt increase of ''P''-wave and ''S''-wave velocities at the depth of , discovered by seismologist

Inge Lehmann Inge Lehmann (13 May 1888 – 21 February 1993) was a Danish seismologist and geophysicist. In 1936, she discovered that the Earth has a solid inner core inside a molten outer core. Before that, seismologists believed Earth's core to be a sin ...

. The thickness is 220 km . It appears beneath

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions In geography, regions, otherwise referred to as zones, lands or territories, are areas t ...

s, but not usually beneath

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

s, and does not readily appear in globally averaged studies. Several explanations have been proposed: a lower limit to the pliable asthenosphere, a

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...

, and most plausibly, depth variation in the

shear wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because th ...

anisotropy Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

. Further discussion of the Lehmann discontinuity can be found in the book ''Deformation of Earth Materials'' by Shun-ichirō Karato.

Notes

General references

* – some historic background.

External links

Inge Lehmann

UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California ...

Career highlights of Inge Lehmann from UCLA
Structure of the Earth {{Geology-stub