# Explain how the refraction of seismic waves as they travel through the Earth provides evidence for the internal structure of the Earth.

> WJEC GCSE Physics (Wales) — 1.7 Seismic waves · Explain · 4 marks

> When an earthquake occurs, seismic waves travel outwards from the focus. Seismometers around the world record the arrival of these waves, but scientists notice that waves do not always travel in straight lines through the Earth.

## Mark scheme (4 marks)

1. Seismic waves change speed / travel at different speeds in different layers of the Earth
2. When seismic waves change speed they change direction / are refracted
3. The pattern / path of refraction indicates where boundaries between layers are located
4. This shows that the Earth is made up of distinct layers / has a layered structure (e.g. crust, mantle, core) with different properties / densities

## Key terms

- [seismic waves](https://www.gradenine.co.uk/glossary/seismic-waves)
- [refraction](https://www.gradenine.co.uk/glossary/refraction)
- [internal structure](https://www.gradenine.co.uk/glossary/internal-structure)

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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