San Andreas Fault

earthquakes · geology · California

A giant crack. The San Andreas Fault is a huge break in Earth's crust that stretches about 750 miles through California. It marks where two of Earth's biggest puzzle pieces, called the Pacific Plate and the North American Plate, meet and grind against each other.

Sliding sideways. The two plates don't move up and down like you might think. Instead, they slide sideways past each other at a rate of about one inch per year, kind of like two blocks of ice rubbing together on a frozen lake.

Different danger zones. Scientists divide the San Andreas Fault into three main segments, and each one has its own personality. Some parts are more likely to cause big earthquakes than others, so scientists watch them very carefully.

Constantly moving. The fault is always shifting and grinding, even when we can't feel it. Over millions of years, this tiny movement adds up to create some of the biggest earthquakes in North America.