The animation at the left shows where in the world earthquakes happened between 1960 and 1995. Each earthquake is shown on the map as a yellow dot. Do you see a pattern to where the dots are found?

Earthquakes do not happen at random locations. They are not equally spaced. Some areas have many earthquakes while other areas have few.

Earthquakes happen when rock below the Earth’s surface moves abruptly. Usually, the rock is moving along large cracks in Earth’s crust called faults. Most earthquakes happen at or near the boundaries between Earth’s tectonic plates because that’s where there is usually a large concentration of faults. Some faults crack through the Earth because of the stress and strain of the moving plates. Other, large faults are the boundary between plates, such as the San Andreas Fault on the North American west coast.

Since earthquakes happen along faults and most faults are near plate boundaries, the yellow dots in the animation are found mostly at the boundaries between Earth’s tectonic plates.

While it is not as common, there are also some faults in the middle of plates. Movement along those faults can cause earthquakes too. For example, many strong earthquakes shook the Mississippi River Valley between December 1811 and March 1812. Although this area is in the middle of the North American plate, there is a large fault. It’s called the New Madrid Fault and movement along it caused the 1811-1812 earthquakes.