GCSE SCIENCE PHYSICS HIGH SCHOOL - Waves - Earthquakes - Structure of the Earth - P Waves - S Waves - Refraction

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Earthquakes - Structure of the Earth - P Waves and S Waves.

The two types of wave which travel through the planet from an earthquake
are called P waves and S waves.
S waves are transverse, P waves are longitudinal.
P waves travel faster than S waves.

In the picture below, P waves are shown in blue and S waves in red.
The earthquake has occurred on the left side of the planet,
the waves are moving from left to right.

Earthquake Waves

The transverse S waves cannot travel through the liquid outer core.
They can travel through the mantle
because the mantle behaves more like a solid than a liquid.
The S waves curve as they move through the mantle
due to refraction as the density of the mantle changes.

The longitudinal P waves can travel through the whole planet.
They also curve with the changing density of both the mantle and the core
(except the wave passing through the centre,
which travels in a straight line, normal to the boundary).
The P waves change direction suddenly
at the boundary between the different layers of the Earth.
This is due to refraction caused by the different densities of the layers.

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