San Francisco, California earthquake, sometime in 1906

An earthquake is when Earth's tectonic plates shake and move Earth's surface. Strong earthquakes damage buildings.

Disturbances in the Earth cause earthquakes. Different tectonic plates are slowly moving. When they get stuck, tension builds up in them. Earthquakes occur when tectonic plates suddenly break free, so they start moving quickly. The first point of an earthquake's rupture is called its hypocenter or focus. The epicenter is the point at ground level directly above the hypocenter.