Elastic-rebound theory

Elastic-rebound theory explains earthquakes as sudden fault slip that releases elastic strain accumulated as rocks deform under tectonic stress, allowing them to rebound toward less strained shapes.

Fault (geology): A fracture or zone of fractures in rock along which the two sides have moved relative to each other. The theory locates earthquake slip on faults, where accumulated strain is abruptly released.
1906 San Francisco earthquake: A major earthquake that ruptured the San Andreas Fault in California on April 18, 1906. Its rupture and ground offsets provided the central case for the theory.
Elasticity (physics): The property of a material that lets it recover its original shape after a deforming force is removed. The theory depends on rocks behaving elastically while strain accumulates.
Geodesy: The science of measuring Earth’s shape, gravity field, and changes in its position over time. Geodetic measurements reveal the gradual deformation that can precede fault rupture.
Viscoelasticity: A material response combining elastic deformation with time-dependent viscous flow. Earth’s crust and mantle relax over time, unlike a purely elastic idealization.
Elastic deformation: A reversible change in a material’s shape or size under stress. It describes how rocks store recoverable strain before a fault ruptures.
San Andreas Fault: A major right-lateral strike-slip fault system in California separating the Pacific and North American plates. The 1906 earthquake’s displacement along this fault anchored the original explanation.
Strain (mechanics): A measure of deformation expressed as change in length or shape relative to an original dimension. Accumulated strain is the stored deformation released in the theory’s earthquake cycle.
Global Positioning System: A satellite-based navigation system that also enables precise measurements of ground position and motion. GPS records crustal strain accumulation and earthquake-related displacement.
Aseismic creep: Slow fault movement that occurs without producing significant earthquake waves. Some tectonic strain is released gradually rather than in the sudden slip the theory emphasizes.

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