Final answer:
The property of an earthquake wave that changes when it moves from one material to another is the wave speed. This occurs due to variations in material density and elasticity which influence the wave's velocity, and it's crucial for locating the epicenter and understanding seismic wave impacts.
Step-by-step explanation:
When an earthquake's waves move from one material to another, the property of the wave that changes is the wave speed. This change in speed happens because different materials have varying densities and elastic properties, which affect how quickly the waves can travel through them. The faster a material's particles can respond to an energy pulse, the faster the wave will travel. P-waves, being longitudinal, can travel through both liquids and solids, while S-waves, which are transverse, can only travel through solids. Since the speeds of P-waves and S-waves are different, this allows seismologists to use the time delay between their arrivals at a seismic station to locate the earthquake's epicenter.
Understanding the difference between longitudinal and transverse waves is crucial because it helps to determine how these waves affect materials differently. Longitudinal waves, like P-waves, compress and expand the material they travel through, while transverse waves, like S-waves, displace the material perpendicular to their direction of travel. This understanding is crucial for assessing earthquake risks, designing structures resistant to seismic activity, and interpreting seismic data to learn about Earth's interior.