Describe the differences between P-waves and S-waves produced by an earthquake.

WJEC GCSE Physics (Wales) — 1.7 Seismic waves · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

When an earthquake occurs, two types of seismic wave travel through the Earth. Seismologists record these waves at stations around the world.

Model answer (4 marks)

P‑waves are longitudinal waves, where particles move in the same direction as the wave propagates.
S‑waves are transverse waves, with particles moving perpendicular to the direction of propagation.
P‑waves travel faster than S‑waves.
P‑waves can move through solids and liquids, whereas S‑waves can only move through solids and are not detected on the far side of the Earth.

Examiner tips

Use the terms longitudinal and transverse; mention particle motion. State the speed comparison. Explain medium difference. Note the shadow zone for S‑waves and detection of P‑waves on the opposite side.

Common mistakes

Confusing longitudinal with transverse. Forgetting that S‑waves cannot travel through liquids. Over‑generalising that both waves travel at the same speed. Not mentioning the shadow zone for S‑waves.

Mark scheme (4 marks)

P-waves are longitudinal waves / S-waves are transverse waves
P-waves travel faster than S-waves
P-waves can travel through solids and liquids / S-waves can only travel through solids
S-waves do not reach the far side of the Earth (shadow zone) / P-waves can be detected on the opposite side of the Earth

Key terms in this question

P-waves · S-waves