Lehmann discontinuity

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)^[2] in Earth's mantle, discovered by seismologist Inge Lehmann.^[3][4][5] It appears beneath continents, but not usually beneath oceans,^[6] and does not readily appear in globally averaged studies. Several explanations have been proposed: a lower limit to the pliable asthenosphere, a phase transition,^[7] and most plausibly, depth variation in the shear wave anisotropy.^[8]

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]