Final answer:
Seismic waves are reflected and refracted at boundaries of materials with different acoustic impedances, due to changes in wave speed and direction between different media such as the layers within Earth.
Step-by-step explanation:
Seismic waves tend to be reflected and refracted at the boundaries between materials of different acoustic impedances. This phenomenon occurs because the waves encounter changes in material properties, which affects their speed and direction. When seismic waves pass from one medium to another with different acoustic impedance, some of the wave energy is reflected back, while the remaining energy is transmitted into the second medium. Higher differences in acoustic impedance lead to a greater proportion of the wave being reflected.
For example, the Earth's interior layers, such as the crust, mantle, and core, have varying acoustic impedances due to differences in composition and state (solid or liquid). The understanding of such internal structures is enhanced by observing the behavior of seismic waves produced by earthquakes. Both P-waves (pressure waves) and S-waves (shear waves) are used in seismology to investigate these layers as they travel at different speeds and are affected differently by the medium through which they move.