An earthquake is the result of a sudden release of “strain” that is built-up between two tectonic boundaries or at a fault line*, usually slipping in opposite directions.

The following video by the California Academy of Sciences shows a computer simulation of an earthquake at the Hayward fault which is one and the most concerning of several faults in California. The most famous fault being the San Andreas fault.

via KQED Science

• A fault is a fracture in the rocks of Earth’s crust. There three main categories of faults: Strike-slip, dip-slip, & Oblique-slip.