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Why Do Earthquakes Happen?

Visitors cross highway 178 next to a crack left on the road by an earthquake Sunday, July 7, 2019, near Ridgecrest, Calif.
Marcio Jose Sanchez
AP Photo
Visitors cross walk on the road next to a crack left on the road by an earthquake Sunday, July 7, 2019, near Ridgecrest, Calif.

Why do earthquakes happen? How do the tectonic plates move underground? How do we stay safe during an earthquake? For this week's show we headed to California to visit Jennifer Strauss at the Berkeley Seismology Lab and we hear from Celeste Labedz at the California Institute of Technology.

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"Why do earthquakes happen?" -Evan, 6, Rhode Island

Other questions in this episode: Why are continents so far apart? Why do buildings sometimes catch fire after earthquakes? Why are there tsunamis after earthquakes?

Earthquakes happen mainly because our earth has something special: tectonic plates.

"The outer layer of the earth isn't one single outer shell like the peel of an apple. It's in several pieces; those are the tectonic plates that can move around the other surface of the earth," says cryoseismologist Celeste Ladedz. "At the places where tectonic plates touch, like in California where the North American plate is up against the Pacific plate, the relative motion between them is what's causing the earthquakes. Plates stay stuck together most of the time because of the friction between them. But, over time, that force builds up and then they'll suddenly slip against each other.  That jolting slip is what an earthquake is. That's what creates the seismic waves that move the ground."

Labedz suggests an image that might help you understand an earthquake. Think about moving a piece of heavy furniture across a thick carpet. When you start pushing, the carpet will hold the furniture in place for a while, but then the force builds up and it moves in a big jerky jolt. That's what's happening in an earthquake!

Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.
Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
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