# Geologists use seismic waves to study the internal structure of the Earth. Explain how the properties of P-waves and S-waves allow scientists to deduce that the Earth has a liquid outer core.

> WJEC A-Level Physics (Wales) — 5.2 Gravitational fields (A-Level only) · Explain · 5 marks

> When a large earthquake occurs, seismic monitoring stations around the world detect the waves that travel through the Earth. Scientists have found that P-waves are detected on the opposite side of the Earth from the earthquake, but S-waves are not detected in a large 'shadow zone' on the opposite side.

## Mark scheme (5 marks)

1. S-waves are transverse waves / S-waves have oscillations perpendicular to the direction of travel
2. S-waves cannot travel through fluids/liquids
3. S-waves are not detected on the opposite side of the Earth / S-waves do not pass through the core
4. P-waves are longitudinal waves / P-waves can travel through all mediums including liquids
5. P-waves are still detected on the opposite side, so the core must be liquid / the fact that S-waves are blocked but P-waves are not shows the outer core is liquid

## Key terms

- [P-waves](https://www.gradenine.co.uk/glossary/p-waves)
- [S-waves](https://www.gradenine.co.uk/glossary/s-waves)
- [seismic waves](https://www.gradenine.co.uk/glossary/seismic-waves)

## Related

- [Revision notes for WJEC A-Level 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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Source: [GradeNine](https://www.gradenine.co.uk/q/geologists-use-seismic-waves-to-study-d03f4504) · Published by Druglandscape Ltd.