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249

earthquakes

OLogy Series
geology
card
249

earthquakes

OLogy Series
geology

The plates that make up the Earth's crust are always moving. When two plates meet, the motion causes lots of pressure to build up. Sometimes the pressure is so great that the plates break loose, causing the ground to tremble in an earthquake. Earthquakes occur all the time, but many are so small we barely feel them.

When earthquakes occur near the coasts, the vibrations can set off huge waves called:

superwaves

tsunamis

titanic waves

Are you right?

Correct!

These enormous waves race across an ocean at hundreds of miles an hour. As they reach shallow waters, they can grow to the size of buildings and cause great damage when they crash on the shore.

Scientists predict that if the two plates along the San Andreas Fault continue to slide past each other at their current rate, in 15 million years:

Los Angeles will fall into the ocean

Los Angeles will move into Mexico

Los Angeles will be next to San Francisco

Are you right?

Correct!

Most earthquakes in California occur along the San Andreas Fault. Los Angeles sits on the Pacific Plate, which is moving north at about 2.3 inches a year. San Francisco sits on the North American Plate, which is moving south.

Ed Mathez, Earth scientist

Although big earthquakes are scary, they make the Earth ring like a bell. And how the Earth rings allows us to understand what's inside.

All earthquakes cause serious damage.

Fact
or
Fiction
?

Fiction

Thousands of earthquakes are detected each year. But most are so small people can't even feel them. About 1 in 5 are felt by people. Only 1 in 5,000 do any damage.

An instrument called a "creepmeter" helps scientists track changes and movement in the Earth's crust.

Fact
or
Fiction
?

Fact

This instrument measures ground movement, or "creep," along a fault line where two plates meet. Another common tool is the seismometer, which records ground vibrations.

Definition: sudden shaking or movement of the Earth's crust
Cause: pressure builds up in rock until the rock breaks
Location: almost anywhere, but most earthquakes occur at plate boundaries
Largest on record: Chile, South America, 1960
Cool fact: The deepest earthquakes occur about 600 km (370 mi) deep, far below the ocean floor.

Image credits: courtesy of USGS; Ed Mathez: courtesy of AMNH.