Introduction
The San Andreas Fault is a geologic fault zone between two tectonic plates that runs from San Francisco south to San Diego in California. It is an area of frequent earthquakes caused by the plates sliding past each other. It is so called because it runs along the San Andreas Valley.
The San Andreas fault was brought dramatically to world attention in 1906 when sudden displacement along the fault produced the great San Francisco earthquake and fire. This earthquake was but one of many that have resulted throughout its life of about 15-20 million years.
Body
The entire San Andreas fault system is more than 800 miles long and extends to depths of at least 10 miles within the Earth. 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.
The Pacific plate is moving northwest in relation to the North American plate, and it is believed that the total displacement along the fault since its formation more than 30 million years ago has been about 350 mi. Movement along the fault causes earthquakes; several thousand occur annually
The basic science is pretty straightforward. The earth lurches from time to time because its outer shell is broken into huge, solid plates floating on a layer of molten rock that has the consistency of Silly Putty. These tectonic plates are constantly jostling each other, like rafts crowded into a small pond, and its along the boundaries where they meet that most quakes are born. The two plates that form California’s infamous San Andreas Fault, the Pacific and the North American plates, are the largest on Earth. And they are moving inexorably in opposite directions.
The Essay on Earthquake zones in Bangladesh
The first seismic zoning map of the subcontinent was compiled by the Geological Survey of India in 1935. The Bangladesh Meteorological Department adopted a seismic zoning map in 1972. In 1977, the Government of Bangladesh constituted a Committee of Experts to examine the seismic problem and make appropriate recommendations. The Committee proposed a zoning map of Bangladesh in the same year. ...
Conclusion
There are records of earthquakes on the southern San Andreas fault going back thousands of years and can estimate an average repeat time for certain segments of the fault. We understand that the Los Angeles Basin is being broadly compressed from north to south due to a ben in the San Andreas, and that the compression is causing the San Gabriel and Santa Monica Mountains to be pushed upward on systems of faults at their bases. Scientists have mapped some of those faults and inferred the existence of others using sophisticated techniques.
Then why can’t we predict earthquakes? One reason could be that for the most part earthquakes process tens of miles below the earth’s surface away from easy observation and they play out over geologic time. Scientists are continually proposing and testing theories to understand the complexities of the plate tectonics. New Microscopes to study the grounds of earthquakes have for the first time made quake prevention something to look forward to in the future.
URL’s
http://quake.wr.usgs.gov/info/essay.html
http://www.encyclopedia.com/articles/11408.html
http://dectionary.msn.com/find/entry.asp?refid=1861701053
http://www.time.com/time/reports/V21/science/cali.html
