San Andreas Fault

Measurements of triangulation lines across the San Andreas Fault before and after its rupture in the 1906 San Francisco earthquake led to the so-called elastic rebound theory for tectonic earthquakes.

As formulated by the American geologist Harry Fielding Reid, the theory explains that a tectonic earthquake occurs when stresses in rock masses have accumulated to a point where they exceed the strength of the rocks, leading to rapid fracture.

These rock fractures usually tend in the same direction and may extend over many kilometers along the zone of weakness.

In the 1906 earthquake the San Andreas Fault slipped for 430 kilometers, with a maximum horizontal fault offset of about six meters.