How do geologists use earthquake waves to study the Earth's interior?

Answer 1

As seismic waves, particularly P-waves, travel through Earth, they pass through the layers of the planet. We can make inferences about the composition and temperature of these layers based on the velocities of the waves. Waves change velocity with density and density is related to both composition and density. S-waves are useful for studying the mantle, but the stop at the outer core because S-wave cannot travel through liquid. P-waves can travel through the planet.