The San Andreas Fault is the most famous fault in the world. Its notoriety comes partly from the disastrous 1906 San Francisco earthquake, but rather more importantly because it passes through California, a highly-populated state that is frequently in the news. And with many research institutions dedicated to studying such an accessible fault, the SAF has become a household name. But what is a fault? And what is the SAF?

A fault is a planar crack in a rock along which slippage has taken place. Most faults are small - even microscopic - and are not important. Some faults are many miles long.

Faults can be classified according to which of the three directions of space the rocks on either side move. When the motion is predominantly vertical, they are called dip slip faults. Dip slip faults with dips less than 45 degrees are called thrust faults.

More Info: www.sanandreasfault.org