Free taster
5 of 6 sections open
X-Raying the Earth
📖 X-Raying the Earth
We can't dig to the Earth's core — the deepest hole ever drilled is only 12 km (Earth's radius is 6,371 km!). So how do we know what's inside? Earthquakes! When earthquakes happen, they send waves through the entire planet. By studying how these waves travel, bend, and where they can't go, scientists have mapped the Earth's interior: a solid inner core, liquid outer core, mantle, and crust. It's like using ultrasound to see inside a body, but for the whole planet!
P-Waves and S-Waves
Earthquakes produce two main types of seismic waves that travel through the Earth:
Earn the mark scheme marks
🧠 Memory Aid
P-waves vs S-waves:
- P-waves = Primary (arrive first) = Push/pull (longitudinal) = Pass through everything (solids and liquids)
- S-waves = Secondary (arrive second) = Shake sideways (transverse) = Stopped by liquid
Earth's layers (outside to inside): "Can My Little Pony Come In?"
Crust — Mantle — (Liquid) outer core — (solid) inner core
Now try it yourself
Quiz · Question 1 of 13
What type of wave is a P-wave (primary seismic wave)?
Tap an answer to check it
This topic in real past papers
Every real exam question we've found on seismic waves, with a full worked answer.