What do earthquakes and seismic waves tell us about the inside of the earth?
they tell us essentially the composition of the layers. By measuring earthquakes from far away, since the waves have to travel through the earth, we can tell what the composition is. Since the waves travel differently through solids, liquids, sediments, and different densities, we can tell what they had to go through by the time it takes for a wave to go from one part of the world to another.
