How Do You Know What's Going on Inside the Earth?

The vibrations pass through the Earth. Do they get delayed in areas that are of different density? Yes. The speed with which they travel depends on the density of the material. So there are other tricks we can use to see exactly what the variations are inside the Earth. When the vibration passes through areas of differentdensity, how big is the delay between these different materials for you to be able to go? Ah, this is Polymer A or Substance B. We would like them and we don't have receivers everywhere. But it means that we know some places in better detail than other places, that's all.