This how it works covers How It Works: Why Seismic Waves Refract Inside Earth 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 6 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ How It Works: Why Seismic Waves Refract Inside Earth
Just like light refracts when passing from one medium to another, seismic waves refract when they pass through layers of different density inside Earth. As depth increases, pressure and temperature change, which changes the density and rigidity of rock — and therefore the wave speed.
Seismic waves generally speed up as they go deeper into the mantle (rock becomes denser and more rigid under pressure). Because speed increases continuously with depth, wave paths curve gradually — like light in a medium with a gradually changing refractive index. This curved path means seismic waves arrive at seismograph stations at unexpected positions, allowing scientists to deduce the density profile of Earth's interior.
When waves cross a sharp boundary (like the mantle-core boundary), there is a sudden change in speed and direction — like light hitting a glass surface — creating the distinct shadow zones observed.
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.