Indirect Evidence for the Structure of the Earth

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Seismic Waves

Vibrations from large earthquakes are detetced as seismic waves by seismographs all around the world. Analysis of many earthquakes over the last 100 years has helped geologists build up a detailed picture of the inside of the Earth.

P and S waves are seismic waves that travel through the layers of the Earth, so are called body waves. The travel:

faster if the rock becomes more rigid and more incompressible

slower if the rock becomes more dense

If the rock loses its rigidity completely, S waves slow down until they stop. So S waves cannot travel through a liquid.

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