Feel the Ground Move

The ground under your feet feels like it never moves, right? But deep below the surface, giant slabs of rock called plates are slowly pushing and rubbing against each other all the time. Sometimes they get stuck, and when they finally slip loose, the ground shakes. We call that shaking an earthquake.

In this lesson you will: (1) explain what causes an earthquake, (2) name the tool scientists use to measure shaking, (3) describe what to do to stay safe during an earthquake, and (4) understand why some places have more earthquakes than others.

The Earth's outer layer is broken into huge puzzle pieces called tectonic plates. These plates move so slowly, only a few centimeters a year, about as fast as your fingernails grow. But where two plates meet, called a fault, they can get stuck against each other. Pressure builds up until the rock suddenly snaps and slides. That sudden slide sends shaking waves through the ground, which is the earthquake you feel.

Scientists called seismologists use a tool called a seismograph to measure how strong an earthquake is. The shaking is measured on a scale where each whole number is about 10 times stronger than the one before it. A magnitude 5 earthquake can rattle dishes off a shelf, while a magnitude 7 can be strong enough to knock down buildings.

If you ever feel the ground shake during an earthquake, remember three steps: Drop to your hands and knees so you don't fall. Cover your head and neck under a sturdy table or desk. Hold on to that table leg so it doesn't shake away from you. Staying away from windows and tall furniture that could fall keeps you even safer.