What is an earthquake? 

What happens when one occurs?

Earthquakes are when the ground under us starts to break or shift away from each other. Then an energy built up from under us is released which causes the ground to shake. Earthquakes happen when a sudden energy at the crust of the earth releases and causes seismic waves. When energy gets released by a fault at the focus. There are 3 different kinds of seismic waves, the first one Primary waves, the second one Secondary waves and the last one surface waves. Seismic waves come from the epicenter of the earthquake.

This image shows an earthquake happening because of plates moving

How would we know when an earthquake is happening?

Scientists have a machine called a Seismograph.  A seismograph is like a printer but it writes lines instead of words. When an earthquake happens the ground shakes and the seismograph picks up the vibration and then the weight on the seismograph moves which then will write down the vibrations on the rotating drum which has a paper type of material on it which will graph the earthquake. It picks up every size and type of seismic wave. 

Seismograph

What do scientist use to measure an earthquake?

Scientists use the Richter Scale which is like a ruler but for earthquakes. It is used to measure the magnitude of the earthquake, which is measuring how big it is. If the line on the seismograph is tall it means that the earthquake is big. If the line is small that means the earthquake was tiny. Scientists look at the lines on the seismograph and use the "Earthquake Ruler" to measure how big the earthquake is.

Magnitude

Richter Scale

What to do if an earthquake is happening

How can you be safe if an earthquake is happening. They can be very scary but don't panic. The first thing you want to do if you're inside you want to get away from windows, objects on walls, and loose items, after that get under something and hold onto it. And if your outside get away from building and tall stuff.