The San Andreas Fault is a geologic continental "transform" extending approximately 810 miles and running through California, parallel to the continental coast.
The San Andreas Fault is the boundary between the Pacific and North American tectonic plates.  This fault zone receives the overall motion between the plates. The motion of the fault is a right-lateral strike-slip.  The fault divides into three segments, a north middle and south, each with their own earthquake risks.  The oldest section of the fault was formed by the subduction of a spreading ridge 30 million years ago.  The likelihood of a megathrust earthquake is being extensively studied by researchers at the University of California who are actively drilling into the fault.
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