The Earth can be divided into four major layers: the inner core, outer core, mantle, and crust. The crust and the upper part of the mantle are like a thin skin on the surface of the Earth.

Unlike the skin on our bodies, though, this skin on the Earth is not all in one piece. Instead, it consists of many pieces that fit together a bit like a jigsaw puzzle.

Scientists call these puzzle pieces tectonic plates. Tectonic plates differ from jigsaw puzzle pieces in that they constantly but slowly move around, sliding past and/or bumping into one another.

The edges of the tectonic plates are called plate boundaries. The rough plate boundaries occasionally get stuck, but the rest of the plates keep moving.

When a plate moves far enough, its edges break free along an area called a fault. When two tectonic plates slip past one another suddenly, the people who live in the area close to the fault experience an earthquake.

The spot on the surface of the Earth directly above where the earthquake occurs underground is called the epicenter of the earthquake. After an earthquake, there are often smaller earthquakes — called aftershocks — that occur in the same place. These aftershocks have been known to continue for weeks, months, and even years after the main earthquake.

Earthquakes can be very destructive. The sudden motion of tectonic plates can cause injuries and serious property damage, especially because there is often little or no advance warning of earthquakes.

When plate boundaries become stuck, their usual energy from motion is stored and builds up until, during an earthquake, it is released suddenly in the form of seismic waves that radiate outward from a fault in all directions. As these seismic waves reach the surface of the Earth, they shake the ground and everything on it.

If you ever experience an earthquake firsthand, it's important to remember and follow a few safety tips:

  • Get low and take cover under a protective object, such as a sturdy table or desk.
  • Hold on and try to stay as steady as possible.
  • Stay inside until the earthquake ends.
  • Stay away from windows, furniture, and other items that could fall on you.
  • If you're in bed, stay there and protect your head with your pillow.
  • If you're outside, move to a clear spot away from buildings, trees, and power lines.
  • If you're in a car, slow down and stop in a clear area until the earthquake stops.

Take earthquake safety seriously! Scientists estimate that there are 500,000 detectable earthquakes in the world each year. Of these, approximately 100,000 of them can be felt, and at least 100 of them cause some kind of damage.

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