Explain why P-waves can be detected on the opposite side of the Earth from an earthquake, but S-waves cannot.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Seismic waves produced by earthquakes travel through the interior of the Earth. Scientists use detectors placed around the world to monitor these waves.
Model answer (4 marks)
P‑waves are longitudinal waves, so they can travel through solids and liquids. S‑waves are transverse waves and can only move through solids. The Earth's outer core is liquid, so S‑waves cannot pass through it and therefore do not reach the opposite side of the Earth.
Examiner tips
- Use the word ‘longitudinal’ for P‑waves and ‘transverse’ for S‑waves. Mention the liquid outer core as the reason S‑waves are blocked. Keep the answer short and to the point – 4 marks.
Common mistakes
- Confusing P‑waves with S‑waves or vice‑versa. Forgetting to state that the outer core is liquid. Giving extra detail about wave speed or types of waves not asked.
Mark scheme (4 marks)
- P-waves are longitudinal waves (that can travel through solids and liquids)
- S-waves are transverse waves (that can only travel through solids, not liquids)
- The Earth's outer core is liquid / molten
- S-waves cannot pass through the liquid outer core, so they do not reach the other side of the Earth
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →