This key facts covers What Seismic Waves Tell Us About Earth's Structure within Seismic Waves for GCSE Physics. Revise Seismic Waves in Waves for GCSE Physics with 13 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 5 of 14 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
🌍 What Seismic Waves Tell Us About Earth's Structure
Key evidence:
- S-wave shadow zone: S-waves don't arrive on the opposite side of Earth from an earthquake — there is a large shadow zone
- This proves there's a liquid layer (outer core) that S-waves cannot pass through
- P-wave shadow zone: P-waves are refracted (bent) by the core, creating a partial shadow zone between about 105° and 140° from the earthquake
- Refraction occurs because the core has a different density from the mantle, causing waves to change speed and direction
- Solid inner core: Some P-waves are detected arriving through the very centre, and their travel times suggest a solid inner core
Quick Check: Why do S-waves not reach the other side of Earth from an earthquake?
S-waves are transverse waves that can only travel through solids. Earth's outer core is liquid, and S-waves cannot pass through a liquid (liquids cannot support shear forces). When S-waves hit the liquid outer core, they are absorbed and cannot travel any further, creating an S-wave shadow zone on the far side.
Practice questions for Seismic Waves
What type of wave is a P-wave (primary seismic wave)?
State two differences between P-waves and S-waves in terms of how the particles move and what materials they can travel through.