Seismic refraction

Seismic refraction is a method scientists use to learn about the ground below the surface. The scientists send out waves (like sound waves) and measure how long it takes for them to bounce off the different layers of ground. By measuring how long it takes for the waves to come back, scientists can figure out how deep each layer of the ground is and what it's made of. All of this together tells us what the ground looks like under the surface.