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The San Andreas Fault Line

Updated on October 22, 2011

The San Andreas Fault line is a boundary line between two moving plates on earths crust in the western California and it is about 1100 km long. One of the two plates between which the San Andreas Fault line is present is the Pacific plate and the other is the North American plate. The San Andreas Fault line divides California into two from Cape Mendocino to the Mexican border.

The San Andreas Fault line is believed to be almost 28 million years old. Over the years the gliding of the two plates beside the line have been causing severe earthquakes. Some of the most deadly earthquakes ever happened in the history of earth were due to the gliding of these plates. The west side usually moves to north causing earthquake along with the movement.

Although there are many other fault lines present on earth’s surface, the San Andreas Fault line is believed to be the most dangerous than all the others. Probably because the plates along the San Andreas move on the sideways instead of the conventional movement of one plate up and other down just like along other fault lines of the world.

On the pacific plate along the San Andreas line cities such as San Diego, Los Angeles and Big Sur are present while the cities of San Francisco, Sierra Nevada and Sacramento are on the North American plate. 

Santa Cruz mountains
Santa Cruz mountains

Different Segments Of The San Andreas Line

The San Andreas line has been divided into many segments. Following are some segments of the San Andreas Fault line:

The Northern Segment Of San Andreas Line

This segment of the San Andreas Fault line is approximately 300 km long and extends from the shelter cove ending along the San FranciscoBay area. Various parts of this segment have been ruptured by many earthquakes that happened along the line.

The famous San Francisco earthquake of 1906 has caused the most damage to the segment. Although the earthquakes of 1957 and 1989 caused damage to the segment, but since their magnitude was not as big as that 1906 earthquake, the damage caused is much less.

A volcanic eruption
A volcanic eruption

The Creeping Segment Of The Line

This segment of the line unlike other segments is in constant yearly movements.

The other sections of the San Andreas line are locked and move only in the case of major earthquakes but this portion has a constant 3 inch movement every year causing minor earthquakes. This time of phenomenon is very rare and is known as a seismic creep. 

San Bernardino Mountains
San Bernardino Mountains

The Central Segment Of The San Andreas Line

Before the great 1906 earthquake, an earthquake of much higher magnitude happened on the 9th of January 1857. This earthquake opened the ground for about 350 km.

The central segment of the San Andreas line in defined by this particular earthquake. Along the San Emigdio Mountains the segment takes a bend and then runs along the south edge of the Mojave Desert.

The Park Fields Segment Of The San Andreas Line

This segment is hardly 30 km long and is located at the centre of the San Andreas. The earthquakes that occur along the park field segment are at maximum 6 magnitude and don’t cause much of the damage.

Documentary On The San Andreas Fault

The San Andreas Fault, in the Carrizo Plain
The San Andreas Fault, in the Carrizo Plain

The Southern Segment Of The San Andreas Line

This segment runs from the Cajon pass and ends at the shores of Slaton Sea running approximately 300 km. At some parts of the segments a seismic creep has been observed.

The segment has not been ruptured since the 1700s and its earthquakes do not cause much harm.

The segment slits into two strands near San Bernardino Mountains.

The Assumptions And Myths About The San Andreas Fault Line

There are many assumptions and predictions regarding the San Andreas Fault line. Many scientists and geologists predicted the line may extend over the years, however no such thing has yet been observed.

There is also a myth regarding the fault line that one day an earthquake so big would be caused that it would rip the entire California a part. There is no doubt that one of the greatest earthquakes ever have been caused along the Fault line of San Andreas which has caused cracks and furrows on the land.

However ever since the 1906 earthquake no major earthquake causing such an extent of damage has occurred along the line.

Now the land above the line is peacefully occupied by the residents who suffer minor shakes once in a while. Will the myths ever come true? Or is there really yet another earthquake on the way far more dangerous than of the earthquakes? The answer can never be given surely.

Presentation On San Andreas Fault


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    • hassam profile imageAUTHOR


      7 years ago from Pakistan

      Thanks for pointing that out! :)

    • EQTactics profile image

      Etienne Luu 

      7 years ago from Pittsburgh, Pennsylvania, United States

      On the video you put "Sand" instead of "San". I am glad to point this out. By the way, nice hub.

    • hassam profile imageAUTHOR


      8 years ago from Pakistan

      Thanks for commenting, will definitely check out your hubs!

    • M. Engebawy, PhD profile image

      M. Engebawy, PhD 

      8 years ago from Overland Park, Kansas, USA

      Great hub! Thanks for the hard work.

      According to the US Geological Survey, the southern segment of San Andreas Fault has the highest probability of generating a large earthquake in southern California with a 67% chance of striking the greater Los Angeles area during the next 30 years. The estimated economic losses in Southern California may reach $213 billion. Check my hub on California Earthquakes for more information!


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