Higher Tier Only: Using Wave Speed to Determine Earth's Structure
Part of Seismic Waves — GCSE Physics
This higher tier covers Higher Tier Only: Using Wave Speed to Determine 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 is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 11 of 14 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
Topic position
Section 11 of 14
Practice
13 questions
Recall
15 flashcards
🎓 Higher Tier Only: Using Wave Speed to Determine Earth's Structure
At Higher tier, you need to explain how scientists use the arrival times and paths of seismic waves to determine Earth's structure quantitatively. Key points:
- Multiple seismograph stations around Earth record the time each wave arrives
- By comparing arrival times from different stations, scientists can calculate the path each wave took
- Where waves speed up or slow down (from travel time calculations), this indicates a change in material density
- The sharp cut-off of S-waves at about 105° from the epicentre marks the start of the shadow zone — the size of this shadow zone tells us the depth of the outer core boundary (~2,900 km)
- The appearance of P-waves again in the deeper shadow zone (the PKIKP phase) tells us the inner core is solid
Quick Check: Which type of seismic wave is evidence for a liquid outer core, and how does it provide this evidence?
S-waves provide evidence for the liquid outer core. S-waves are transverse waves that can only travel through solids — they cannot travel through a liquid (liquids cannot support shear forces). The fact that S-waves are detected at seismograph stations up to about 105° from the earthquake, but not beyond, creates an S-wave shadow zone. This shadow zone can only be explained if there is a liquid layer inside the Earth that the S-waves cannot pass through — this is the outer core.