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Contents of 8.2 How do earthquakes help make images of Earth's interior?

8.2 How do earthquakes help make images of Earth's interior?

• Earthquakes produce surface waves, and body waves: P (primary) and S (secondary) that travel through the planet. P and S waves reflect and refract when encountering boundaries with materials.
• Seismograms are records of earthquake waves detected by seismometers. The time needed for these waves to reach the instruments reveals their velocity.
• Travel-time curves reveal that, in general, seismic wave velocity increases deeper into Earth. Shadow zones where S, P, or both waves are not recorded reveal that Earth has a liquid center surrounding a solid inner core at 5155-6371 km depth.