20 March 2010
San Andres Fault Summary
The San Andreas Fault is a crack in the Earth's crust in California, which is about 1100 kilometers long. Since 1857, 1906 and 1989 many famous earthquakes have occurred along it. It is the boundary between the North American and Pacific lithospheric plates. Geologists have learned that the Earth's crust is fractured into a series of "plates" that have been moving very slowly over the Earth's surface for millions of years. Two of these moving plates meet in western California; the boundary between them is the San Andreas Fault. The Pacific Plate (on the west) moves northwestward relative to the North American Plate (on the east), causing earthquakes along the fault. The San Andreas is the "master" fault of an intricate fault network that cuts through rocks of the California coastal region. The entire San Andreas Fault system is more than 800 miles long and extends to depths of at least 10 miles within the Earth. In detail, the fault is a complex zone of crushed and broken rock from a few hundred feet to a mile wide. Many smaller faults branch from and join the San Andreas Fault zone. Furthermore, The San Andreas fault is a transform or strike-slip fault that moves sideways, rather than the more common faults that move up on one side and down on the other. Nearly all transform faults are short segments that occur in the deep sea, but the few that form plate boundaries on land are noteworthy and dangerous. The San Andreas Fault began forming about 20 million years ago with a change in plate geometry that began as a large oceanic plate began subducting beneath California. As it continues to subduct, the San Andreas Fault will continue to grow, perhaps to twice today's length. In conclusion, the San Andreas Fault is very important in the history of earthquake science, but it's not just important to geologists. It has even helped create California's unusual landscape and its rich...