San Andreas fault earthquake. Artwork of a section through the San Andreas fault in California, USA, showing the lateral movement of plates causing an earthquake. San Andreas is a strike-slip fault, where the Pacific tectonic plate (left) moves against the North American plate (right). Each plate is pushed in the direction of the yellow arrows, but frictional forces prevent them moving. Over time, the pressure builds until it exceeds the frictional force, and the plates suddenly move relative to each other, releasing the stored energy as seismic waves. These waves can cause huge damage to buildings and strutures over a wide area.