What causes earthquakes?

The ground under your feet feels solid and still. But sometimes it shakes and rumbles all by itself! This is called an earthquake. What could make the whole Earth wobble?

Earth is like a cracked egg

The hard outer surface of our planet is not one smooth shell. It is broken into giant pieces called plates. Picture a cracked eggshell, with the pieces fitting together.

These plates are enormous — whole countries sit on top of them. And here is the surprise: the plates are slowly moving all the time, sliding around very, very slowly.

When plates slip

The plates push and rub against each other along their edges. Most of the time they are stuck tight, like two heavy boxes pressed together.

Pressure builds up and up. Then, suddenly, the plates slip past each other with a giant jolt. That sudden movement sends shaking waves through the ground — and that is an earthquake!

Feeling the shake

The shaking can be tiny, so small that only special machines notice it. Or it can be big enough to rattle windows. Most earthquakes are very gentle, and they end quickly.

Wonder fact: Earth’s plates move about as fast as your fingernails grow — so slow you would never see it, but enough to shape mountains and oceans over millions of years!