Earthquake is a sudden shaking of the ground caused by movement in Earth’s outermost layer, called the crust. The Earth looks solid, but it’s actually extremely active just beneath the surface. There are many different types of earthquakes, but all cause vibrations that we feel as shaking.
Most earthquakes occur when two blocks of the Earth’s crust move past each other. The point on the ground where this happens is called a fault. Earthquakes are generated by the release of energy stored in the crust. This energy is released in a combination of radiated seismic waves, frictional heating of the fault surface and cracking of the rock.
Scientists use seismometers to record the shaking of the Earth. The results are shown on a plot of the ground’s vibrations, called a seismogram. The length of the wiggly lines on the graph shows how big the earthquake was. A short wiggly line means a small earthquake; a long wiggly line means a large one.
We can’t predict when or where an earthquake will happen. But we can say that it’s very dangerous to be outside when an earthquake occurs. If you’re indoors, drop to the floor, cover your head and neck, and hold on to something sturdy until the shaking stops. If you’re outside, move away from buildings, tall trees, streetlights and power lines.