A longstanding theory in geology to explain how earthquakes form suggest that rock on either side of a fault slowly deforms over time, until it suddenly snaps back into its original shape, causing the quake. Reid's theory was the first to satisfactorily account for earthquakes, and has been supported by many GPS measurements, among other evidence. Before this theory, it was thought that ruptures of the surface were the result of strong ground shaking rather than the converse suggested by this theory.
Following the great 1906 San Francisco earthquake, Henry Feilding Reid examined the displacement of the ground surface around the San Andreas Fault.
From his observations he concluded that the earthquake must have been the result of the elastic rebound of previously stored elastic strain energy in the rocks on either side of the fault.
Now a study of major earthquakes in Chile challenges this theory. A team led by Cornell University geologist Richard Allmendinger, who examined temblors of magnitude 7 or greater in Chile's Atacama Desert, found permanent deformations in the Earth's crust.
For more information about earthquakes refer to http://goo.gl/AgS6y
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