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Earthquakes: Tremors from Below - What Causes the Earth to Shake?
Earthquakes: Tremors from Below - What Causes the
Earth to Shake?
This text is provided courtesy of OLogy, the American Museum of Natural History's website for kids.
What Causes the Earth to Shake?
Tsunamis like the one in Samoa are triggered by large undersea earthquakes. To understand how
tsunamis form, let's first take a look at what causes earthquakes. Most earthquakes happen at the edges
of tectonic plates, the big pieces of Earth's crust that make up its outer shell. These plates fit together
like a puzzle, but they are always moving very slowly, about one or two inches per year. Where the
edges of the plates meet, three things can happen. Plates can collide, separate, or grind against each
other. The movement between two plates can trigger earthquakes.
When Plates Collide
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Earthquakes: Tremors from Below - What Causes the Earth to Shake?
When plates collide, sometimes one plate sinks, or subducts, below another one. This can trigger an
earthquake. When earthquakes cause the ocean floor to move, the water moves, too. Columns of water
travel across the ocean and grow taller as they approach land, becoming a tsunami.
When Plates Grind
When the edge of one plate grinds against another, it sometimes gets stuck and pressure builds up. When
it finally breaks loose, rocks break, releasing energy in the form of a seismic wave, or earthquake.
ReadWorks.org · © 2017 ReadWorks®, Inc. All rights reserved.
© 2015 American Museum of Natural History. All rights reserved. Used by Permission