How do seismologists use earthquake waves to infer Earth's internal layers?
Quick Answer
They study how P waves and S waves change speed, bend, or stop as they move through Earth. Those patterns reveal a crust, mantle, liquid outer core, and solid inner core.
The Full Story
Earthquakes release seismic waves that travel through the planet in different ways. P waves can move through solids and liquids, while S waves only travel through solids. When these waves reach boundaries inside Earth, they refract, reflect, or disappear, producing time delays and shadow zones detected by seismometers. That information showed that Earth has a layered interior rather than being uniform. It also helped identify the liquid outer core, first inferred from wave behavior in the early 20th century.
Key Facts
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"Earthquake waves are the X-ray that lets us see inside the planet."
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