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Earth and Space Sciences · Glossary

What is Seismic discontinuity?

Definition 11.5 High School Earth and Space Sciences · Chapter 11 — Seismic Waves Reveal the Interior

A seismic discontinuity is a surface inside the Earth across which the speed of seismic waves changes suddenly — over a thickness much smaller than the length of the waves.

The direct wave and the head wave (to scale: crust 30\, km thick). The head wave goes down at the critical angle i_c, runs along the top of the mantle and comes back up at i_c; along its whole path on the Moho it sends waves up to the surface (dashed). It reaches no station closer than 2h i_c, about 71\, km here.
The direct wave and the head wave (to scale: crust 30 km30\,\mathrm{km} thick). The head wave goes down at the critical angle ici_c, runs along the top of the mantle and comes back up at ici_c; along its whole path on the Moho it sends waves up to the surface (dashed). It reaches no station closer than 2htan⁡ic2h\tan i_c, about 71 km71\,\mathrm{km} here.
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