# A geologist is studying seismic waves produced by an earthquake. The geologist notices that some monitoring stations stop receiving wave signals when the waves reach a layer of liquid rock deep underground. Explain, using your knowledge of P-waves and S-waves, why some monitoring stations stop receiving signals while others continue to receive signals.

> WJEC A-Level Physics (Wales) — 5.3 Electric and magnetic fields (A-Level only) · Explain · 5 marks

> Earthquakes release energy in the form of seismic waves that travel outward from the earthquake's source. Monitoring stations are placed at various locations on Earth's surface to detect these waves.

## Mark scheme (5 marks)

1. S-waves are transverse waves (oscillations perpendicular to direction of travel/energy transfer)
2. S-waves cannot travel through fluids / liquids
3. Stations that stop receiving signals are those that can only be reached by S-waves passing through the liquid layer
4. P-waves are longitudinal waves (oscillations parallel to direction of travel/energy transfer)
5. P-waves can travel through all mediums including fluids / liquids, so other stations continue to receive signals

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-geologist-is-studying-seismic-waves-60f1af4e) · Published by Druglandscape Ltd.