What is the elastic rebound theory?

The elastic rebound theory was developed by Harry Fielding Reid, an American geophysicist who was studying the 1906 San Francisco earthquake.

He observed that points on the Earth's surface distant from the San Andreas fault had gradually moved prior to the earthquake whereas points on the surface directly on and around the fault had not.

During the earthquake the points next to the fault zone which had originally been static had suddenly shifted to match up with the points at a greater distance from the locked fault zone.

He concluded that this was due to the accumulation of elastic strain within the Earth's crust around the fault zone and that when the stress that caused this strain exceeded the strength of the rock mass or fault zone in the crust it suddenly ruptured. This caused the stored energy (termed elastic potential energy) to be released in one instant, causing an earthquake, and also meant that the rock mass around the fault zone that had originally been locked in position, snapped or rebounded to match the position of the rock mass at a greater distance from the fault. As such he coined the term "elastic rebound" to describe this phenomenon.

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