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San Andreas Fault

Article ID: 35
Last updated: 12 Aug, 2014

At 5:12 a.m., April 18, 1906, a powerful earthquake happened along the northern San Andreas fault segment. 

The San Andreas fault zone is the major fault system in California.  It is the boundary between the Pacific and North American tectonic plates. 

Here is a typical slideslip sequence of the two plates which resulted in the 1906 earthquake.

The epicentre of the San Francisco has been identified as Olema, California. 

The stunningly picturesque Olema Valley has a dark side...since it rests on top of the San Andreas fault.  The best place to view the evidence of the 1906 earthquake is at the self-guided trail at Bear Valley Centre, Olema

The posts in these photographs show the line of the slippage which occurred during the 1906 earthquake.

The maximum surface displacement (offset) occured near Olema. This is illustrated by the photograph of this fence at Olema.

It was once continuous.  The horizontal slippage can clearly be seen!  This horizontal movement was unexpected, and puzzled geologists at the time. The maximum offset here was 4.7 m.

At Alder Creek the San Andreas fault leaves the mainland and goes into the Pacific Ocean, crossing Manchester State Park. 

Manchester State Park, which is located in Mendocino County off Coast Highway offers some of the most spectacular coastal scenery in the world.

The Future? 

Well, it is just a matter of time before the ‘ big one’ happens!  By US Geological Survey estimates, the odds (place your bets now!) are two to one that in the next 30 years a major earthquake will hit one of the three major faults in the Bay Area: the San Andreas Fault, the Hayward Fault, or the Rogers Creek Fault (which goes from San Pablo Bay to the West Marin coast).  The shaking, geologists predict, is likely be more than twice as vigorous as it was during the 1989 Loma Prieta earthquake and will, as a consequence of this increased activity, be much more destructive. 

Article ID: 35
Last updated: 12 Aug, 2014
Revision: 1
Views: 92
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