What is the San Andreas Fault?

The San Andreas Fault is a long crack in the earth's crust that extends 970 kilometers through California, in the USA. It runs along the edges of the tectonic plates cerrying the Pacific Ocean and North America. These plates have shifted about 300 kilometers over the past 15 million years. They continue to move about 6 cm each year, building up emormous stresses in the crust. Along the fault line, the ground bulges, cracks open up and roads and railways develop a noticeable kink. The San Andreas Fault is carefully monitored because it is ewxpected to slip at any time.