Fault (geology)

A fracture or zone of fractures in rock along which the sides have moved relative to each other. Faults accommodate deformation and can generate earthquakes.

Fault plane: The surface along which displacement occurs within a fault. It is the surface whose orientation and motion define a fault’s geometry.
Stress (mechanics): A measure of internal force per unit area within a material. Applied stress drives the deformation and failure that create faults.
Earthquake: Ground shaking caused by the rapid release of energy in Earth’s crust or upper mantle. Sudden slip on a fault is the source of most tectonic earthquakes.
Normal fault: A dip-slip fault in which the hanging wall moves downward relative to the footwall. It records extension, one common regime of fault formation.
Fault scarp: A step or slope at Earth’s surface formed by displacement on a fault. Surface rupture can turn fault slip into a visible landform.
Strain (materials science): The deformation of a material expressed relative to its original size or shape. Fault displacement is one way rocks accommodate strain.
Paleoseismology: The study of prehistoric earthquakes using geological evidence, especially fault ruptures and sediments. Trenches across faults can reveal earthquakes older than written records.
Reverse fault: A dip-slip fault in which the hanging wall moves upward relative to the footwall. It records shortening, opposite to the extension associated with normal faults.
Stick-slip motion: A cycle in which friction holds two surfaces, then sudden slipping releases stored elastic energy. Fault surfaces can alternate between locked periods and rapid earthquake-producing slip.
Brittle deformation: Permanent deformation by fracturing or breaking rather than continuous flow. Faulting is a principal form of brittle deformation in rock.

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