Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves, forming an earthquake. The regions of higher friction along a fault plane, where it becomes locked, are called asperities. Owing to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The light layer of rock shows the displacement. See also: Fault mechanics Normal fault in La Herradura Formation, Morro Solar, Peru. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. However, the term is also used for the zone of crushed rock along a single fault. Ī fault zone is a cluster of parallel faults. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. Ī fault plane is the plane that represents the fracture surface of a fault. Faults may also displace slowly, by aseismic creep. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements.

Strike slip fault hanging wall footwall