The San Andreas Fault is one of the most widely studied faults in the world. Scientists use an array of methods in collecting data and providing analysis of fault characteristics both past and present. Presently there are many differing hypothesis and models used to describe crustal movements and deformation within the Pacific and North American plate boundary. Historical earthquakes along this fault have proven to be rather large and devastating. This is important since the San Andreas Fault runs along many highly populated areas throughout Northern and Southern California. Through further research and analysis of this fault system scientists hope to solve the some of the unknowns of plate tectonics and better predict when and where an earthquake will take place.
The San Andreas Fault is a strike-slip fault located on the boundary of two tectonic plates in the Earth’s lithosphere; the Pacific plate on the West and North American plate on the East. This intricate fault system contains a network of faults extending from Northern to Southern California. It is one of the most accessible and widely studied faults in the world. One of the distinct characteristics of the fault is the contrast of rock types on either side, brought together from long distances by millions years of movement. This movement generates several thousand earthquakes annually. By analyzing past and present day movements and configurations of the San Andreas Fault scientists hope to better understand the faults role in plate tectonics and unlock the key to earthquake prediction. Geographic and Physical Location
The San Andreas Fault extends some 1,100 kilometers almost the entire length of California from Eureka to Brawley (Figure 1). The fault is the boundary between the North American and Pacific lithospheric plates. The fault is broken into the following segments: * Northern Segment - Extends approximately 300km from Shelter Cove to San Juan Batista, this entire segment ruptured in 1906, known as the San Francisco earthquake. * Creeping Segment – Extends from San Juan Batista south to Parkfield, unlike other segments which are “locked” this segment has a steady movement of approximately 3 centimeters per year (aseismic creep).
* Parkfield Segment – Extends only 30 km, this is the center of the San Andreas Fault, characteristics include lack of human disturbance, and it is the site of the SAFOD Drilling Project. * Central Segment – Extends 350 km from Cholame to the Cajon Pass through the Mojave Desert. Traverses the San Emigdio and San Gabriel Mountains. * Southern Segment – Extends approximately 300 km from the Cajon Pass to the Salton Sea, this segment has not ruptured since some time before 1700, and it is widely considered that this segment is overdue for a magnitude “8” earthquake. The San Andreas Fault is a transform or strike-slip fault. It is the sliding boundary between the Pacific Plate and the North American Plate. Over the past 5 million years the North American Plate has been moving southeast while the Pacific Pate moves northwest. The plates are sliding slowly past each other at a rate of about 2-3 inches per year, however this no a steady movement but an average movement, the plates may remain “locked” relatively motionless as they push against one another. Then suddenly the built up pressure is released and the plates along the fault slip and move. This slippage and release of energy sends seismic waves in all directions, which we feel as earthquakes. Historical Earthquakes along the San Andreas Fault
At 5:12 a.m. on April 8, 1906 the initial foreshock of the Great San Francisco earthquake shook the San Francisco Bay Area, approximately 20 to 25 seconds later the actual earthquake was felt, with an epicenter near San Francisco the violent shaking lasted 45 to 60 seconds. Buildings were destroyed and fires broke out...