We are heading to our third stop, California, to see an
example of a transform boundary in the San Andreas fault zone.
At a transform boundary, two plates are sliding horizontally past one another. Most
transform faults are found on the ocean floor. The two plates grind against
each other, creating friction, and forming lots of earthquakes and strange land
arrangements. They commonly equalize active spreading ridges, producing zigzag
plate boundaries, and are generally defined by earthquakes. Although most occur in the ocean, some occur
on land.
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| http://www.gweaver.net/techhigh/projects/period1_2/Yellowstone/Plate%20Tectonics.html |
The San
Andreas fault zone in California is a transform boundary that connects the East
Pacific Rise, a divergent boundary to the south, with the South Gorda-Juan de
Fuca-Explorer Ridge, another divergent boundary to the north. The San Andreas
is one of the few transform faults exposed on land. The San Andreas fault zone,
which is about 1,300 kilometers long and in places tens of kilometers wide, cuts
through two thirds of the length of California. Along it, the Pacific Plate has
been grinding horizontally past the North American Plate for 10 million years,
at an average rate of about 5 centimeters per year. The movement at this
boundary has caused many earthquakes. The presence of the San Andreas boundary was brought to attention on
April 18, 1906, when sudden displacement along the fault produced the great San
Francisco earthquake and fire. The earthquake took about 700 lives and caused millions of dollars
worth of damage in California from Eureka to Salinas and beyond. The earthquake
was felt as far away as Oregon and central Nevada, and was estimated at a magnitude
of 8.3 on the Richter scale. On May 18,
1940, an earthquake of a magnitude of 7.1 occurred along a previously
unrecognized fault in the Imperial Valley. Clearly, this fault is part of the
San Andreas transform boundary.
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| http://en.wikipedia.org/wiki/San_Andreas_Fault |
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