# Explain how scientists use P-waves and S-waves produced by earthquakes to determine that the Earth has a liquid outer core.

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

> Seismic waves produced by earthquakes travel through the Earth and are detected at monitoring stations across the world. Scientists have used these waves to build up a picture of the Earth's internal structure.

## Mark scheme (5 marks)

1. P-waves are longitudinal seismic waves that can travel through all mediums (solids and fluids)
2. S-waves are transverse seismic waves that cannot travel through fluids/liquids
3. A shadow zone exists on the opposite side of the Earth where S-waves are not detected
4. P-waves are still detected on the opposite side of the Earth, showing they have passed through the core
5. Because S-waves are blocked but P-waves pass through, the outer core must be liquid/fluid

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](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/explain-how-scientists-use-p-waves-and-43b02e0c) · Published by Druglandscape Ltd.