Seismic Waves and the Earth's Structure

This lesson covers seismic waves and how they provide evidence for the internal structure of the Earth — as required by the Edexcel GCSE Physics specification (1PH0), Topic 4: Waves. You need to understand the properties of P-waves and S-waves, and explain how the behaviour of these waves reveals what is inside the Earth.

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What Are Seismic Waves?

Seismic waves are waves of energy that travel through the Earth, typically produced by earthquakes (but also by explosions and volcanic eruptions). They originate from the focus of an earthquake (the point underground where the rock fractures) and radiate outward in all directions.

Seismic waves are detected by instruments called seismographs (or seismometers). The record they produce is called a seismogram.

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Types of Seismic Waves

There are two main types of seismic waves that travel through the body of the Earth:

P-waves (Primary Waves)