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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. 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.
Types of faulting. Anderson's theory of faulting, devised by Ernest Masson Anderson in 1905, is a way of classifying geological faults by use of principal stress. [1] [2] A fault is a fracture in the surface of the Earth that occurs when rocks break under extreme stress. [3] Movement of rock along the fracture occurs in faults.
Figure 3 is an E-W seismic line at Svalbard area showing footwall, hanging wall and the geometry of sedimentary layers around the fault plane. Fig. 3. Seismic line showing sedimentary layers, footwall and hanging wall of a growth fault: Modified after Bjerkvik, 2012 Accompanied structures. Growth faults have two blocks.
Detachment fault. A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. [1] Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade metamorphic footwalls that are called metamorphic core complexes.
Extensional faults form parallel to the axis of the rift. An extensional fault may be seen as a crack in the crust that extends down at an angle to the vertical. As the two sides pull apart, the hanging wall ("hanging over" the sloping fault) will move downward relative to the footwall. A rift basin is created as the crust thins and sinks.
A graben is a valley with a distinct escarpment on each side caused by the displacement of a block of land downward. Graben often occur side by side with horsts. Horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward ...
Lewis Overthrust. The Lewis Overthrust is a geologic thrust fault structure of the Rocky Mountains found within the bordering national parks of Glacier in Montana, United States and Waterton Lakes in Alberta, Canada. The structure was created due to the collision of tectonic plates about 59-75 million years ago that drove a several mile thick ...
Rollover anticlines are anticlines related to extensional normal faults. They must be differentiated from fault-propagation folds, which are associated with reverse faults. A rollover anticline is a syn-depositional structure developed within the downthrown block (hanging wall) of large listric normal faults. Such faults are typically regional ...