# A major earthquake occurs and seismometers are placed at different distances from the epicentre. Explain why P-waves are always detected before S-waves at any given seismometer station.

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

> Seismometers around the world record vibrations caused by earthquakes. Both P-waves and S-waves are produced at the same moment during an earthquake.

## Mark scheme (4 marks)

1. P-waves are longitudinal waves and S-waves are transverse waves
2. P-waves travel faster than S-waves through the same material
3. Both types of wave are produced at the same time / same source (epicentre)
4. Because P-waves travel faster over the same distance, they arrive at the seismometer first

## Key terms

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

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

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-major-earthquake-occurs-and-seismometers-5a8d5dd6) · Published by Druglandscape Ltd.