__NOTOC__ In

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, the elastic-rebound theory is an explanation for how

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

is released during an

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

. As the Earth's crust deforms, the rocks which span the opposing sides of a fault are subjected to

shear stress Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...

. Slowly they deform, until their internal rigidity is exceeded. Then they separate with a rupture along the fault; the sudden movement releases accumulated energy, and the rocks snap back almost to their original shape. The previously solid mass is divided between the two slowly moving plates, the energy released through the surroundings in a

seismic wave A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large ma ...

Theory

After the great

1906 San Francisco earthquake At 05:12 AM Pacific Time Zone, Pacific Standard Time on Wednesday, April 18, 1906, the coast of Northern California was struck by a major earthquake with an estimated Moment magnitude scale, moment magnitude of 7.9 and a maximum Mercalli inte ...

, geophysicist

Harry Fielding Reid Harry Fielding Reid (May 18, 1859 – June 18, 1944) was an American geophysicist. He was notable for his contributions to glaciology and seismology, particularly his theory of elastic rebound that related faults to earthquakes. He was a pr ...

examined the displacement of the ground surface along the San Andreas Fault in the 50 years before the earthquake.Reid, H.F., ''The Mechanics of the Earthquake, The California Earthquake of April 18, 1906; Report of the State Investigation Commission,'' Vol.2, Carnegie Institution of Washington, Washington, D.C. 1910 He found evidence for 3.2 m of bending during that period. He concluded that the quake must have been the result of the elastic rebound of the strain energy stored in the rocks on either side of the fault. Later measurements using the

global positioning system The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...

largely support Reid's theory as the basis of seismic movement.

Explanation

The two sides of an active but locked fault are slowly moving in different directions, where elastic strain energy builds up in any rock mass that adjoins them. Thus, if a road is built straight across the fault as in Time 1 of the figure panel, it is perpendicular to the fault trace at point E, where the fault is locked. The overall fault movement (large arrows) causes the rocks across the locked fault to accrue elastic deformation, as in Time 2. This deformation may build at the rate of a few centimeters per year. When the accumulated strain is great enough to overcome the strength of the rocks, the result is a sudden break, or a springing back to the original shape as much as possible, a jolt which is felt on the surface as an earthquake. This sudden movement results in the shift of the roadway's surface, as shown in Time 3. The stored energy is released partly as heat, partly in alteration of the rock, and partly as a

References

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External links

* https://earthquake.usgs.gov/earthquakes/events/1906calif/18april/reid.php Plate tectonics 1906 San Francisco earthquake Seismology