physics

Lehmann discontinuity

Lehmann discontinuity is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lehmann discontinuity rather than just read about it. In short: The Lehmann discontinuity is an abrupt increase of P-wave and S-wave velocities at the depth of 220 km (140 mi) in Earth's mantle, discovered by seismologist Inge Lehmann. It appears beneath continents, but not usually beneath oceans, and does not readily appear in globally averaged studies.

Key takeaways

Lehmann discontinuity belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lehmann discontinuity to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lehmann discontinuity from memory before moving on to harder problems.

Reference excerpt

The Lehmann discontinuity is an abrupt increase of P-wave and S-wave velocities at the depth of 220 km (140 mi) in Earth's mantle, discovered by seismologist Inge Lehmann. 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.

Notes

General references P. Caloi (1967). "The "20° Discontinuity"". In H. E. Landsberg, J. Van Mieghem (ed.). Advances in geophysics, Volume 12. Academic Press. p. 167 ff. ISBN 0-12-018812-0. – some historic background.

Further reading Shun-ichirō Karato (2008). Deformation of earth materials: an introduction to the rheology of solid earth. Cambridge University Press. p. 318. ISBN 978-0-521-84404-8.

External links Inge Lehmann, UCLA Career highlights of Inge Lehmann from UCLA

Illustrations

Worked examples

Example 1 — a first encounter with Lehmann discontinuity

Start with the simplest possible case. Write down what Lehmann discontinuity claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lehmann discontinuity before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lehmann discontinuity ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lehmann discontinuity

In research: Lehmann discontinuity appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lehmann discontinuity in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lehmann discontinuity is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geophysics stubs, Structure of the Earth, Tectonics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Lehmann discontinuity outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Lehmann discontinuity” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Lehmann discontinuity in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lehmann discontinuity means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lehmann discontinuity out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lehmann discontinuity in simple terms?

Why does Lehmann discontinuity matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lehmann discontinuity?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lehmann discontinuity.