An earthquake is when the ground shakes and moves suddenly. It happens because there are big chunks of rock underneath us called tectonic plates that shift and move around. When the plates shift, it causes the ground to shake and move. We never know when an earthquake will happen, but they can cause a lot of damage. Some earthquakes happen in one place, like in a certain city, and others can happen far away. Earthquakes can sometimes make tall buildings shake, and can even cause avalanches or tsunamis.