# Earthquakes produce two types of seismic wave: P-waves and S-waves. Scientists monitoring a distant earthquake detect P-waves at a recording station but do not detect any S-waves. Explain the difference between P-waves and S-waves, and use this to explain why only P-waves are detected at the recording station.

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

> When an earthquake occurs, it releases energy in the form of seismic waves that travel through the Earth. Scientists use networks of recording stations around the world to detect these waves.

## Mark scheme (5 marks)

1. P-waves are longitudinal waves (oscillations parallel to the direction of travel/energy transfer)
2. S-waves are transverse waves (oscillations perpendicular to the direction of travel/energy transfer)
3. S-waves cannot travel through fluids / liquids
4. The Earth has a liquid outer core (through which the seismic waves must pass)
5. P-waves can travel through all mediums (solid and fluid/liquid), so they pass through the liquid outer core and reach the recording station; S-waves cannot, so they are blocked

## 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 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/earthquakes-produce-two-types-of-seismic-5f923512) · Published by Druglandscape Ltd.