Earthquake

An earthquake is sudden ground shaking caused mainly by energy released as rocks slip along a fault, or by volcanic activity. Its seismic waves can travel far beyond the rupture.

Fault (geology): A fracture or zone of fractures in rock along which the sides have moved relative to each other. Earthquakes commonly begin when accumulated stress drives sudden slip along a fault.
Seismic hazard: The probability and severity of earthquake-related ground effects at a location over a specified period. Hazard estimates translate earthquake occurrence into expected local shaking and related effects.
1906 San Francisco earthquake: A major 1906 earthquake on the San Andreas Fault that devastated San Francisco and nearby areas. Its mapped rupture helped establish the connection between fault slip and earthquakes.
Volcanic earthquake: An earthquake caused by magma movement, volcanic pressure changes, or related activity. Its source is volcanic processes rather than primarily tectonic fault slip.
Elastic rebound theory: A theory that earthquakes occur when strained rocks suddenly slip, releasing stored elastic energy. It explains how gradual deformation becomes abrupt fault movement and seismic waves.
Earthquake engineering: The design and assessment of structures to withstand earthquake effects. Engineering choices determine how buildings respond to strong ground motion.
1960 Valdivia earthquake: A magnitude 9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake. Its immense subduction-zone rupture shows how earthquake size scales with fault dimensions.
Induced seismicity: Earthquake activity triggered or altered by human activities such as fluid injection or reservoir filling. It distinguishes human-triggered events from earthquakes driven by natural tectonic stress alone.
Seismic wave: A wave of energy that travels through Earth or along its surface, often generated by an earthquake. These waves carry rupture energy outward and create ground motion.
Liquefaction: The loss of soil strength when saturated sediment behaves more like a liquid under shaking. Earthquake shaking can destabilize waterlogged ground beneath structures.

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