In this exercise you are going to measure the size of the Earth's molten outer core.

First of all you need to start an earthquake (or detonate an underground nuclear test!)

1. Click at a point on the Earth's surface to trigger the Earthquake.
2. Move the seismometer around the surface of the Earth and observe the resultant P and S waves.
3. Now click at the points where the S waves appear/disappear.
4. When you have found the two points, two arcs will be displayed, showing the path of P waves from the epicentre to the start points of the S wave shadow zone.
5. Click and drag near the centre of the earth. A red circle, representing the outer core, will appear. Drag this outwards until it touches the two black arcs. Note down the radius of the outer core.

Check your answer here.