How can layers within earth be identified by means of seismic waves?

Layers within the Earth can be identified through seismic waves by analyzing how these waves travel and change speed as they pass through different materials. Seismic waves, generated by earthquakes or artificial sources, are classified into two main types: P-waves (primary waves) which are compressional and travel through solids and liquids, and S-waves (secondary waves) which are shear waves that only move through solids. By studying the arrival times and paths of these waves at various seismic stations, geologists can infer the properties and boundaries of Earth's layers, such as the crust, mantle, and core. Variations in wave speed and behavior, such as reflection and refraction, provide critical information about the composition and state of each layer.