An extensional fault is a fault caused by stretching of the Earth's crust. Stretching reduces the thickness and horizontally extends portions of the crust and/or lithosphere. In most cases such a fault is also a normal fault, but may create a shallower dip usually associated with a thrust fault. Extensional faults are generally planar. If the stress field is oriented with the maximum stress perpendicular to the Earth's surface, extensional faults will create an initial dip of the associated beds of about 60° from the horizontal. The faults will typically extend down to the base of the seismogenic layer. As crustal stretching continues, the faults will rotate, resulting in steeply-dipping fault blocks between them.
>>>PUT SHARE BUTTONS HERE<<<
In this Dossier
Extensional fault in the context of Rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side. Where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the rift area may contain volcanic rocks, and active volcanism is a part of many, but not all, active rift systems.
Major rifts occur along the central axis of most mid-ocean ridges, where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates.
Extensional fault in the context of Depocentre
A depocenter or depocentre in geology is the part of a sedimentary basin where a particular rock unit has its maximum thickness. Depending on the controls on subsidence and the sedimentary environment, the location of a basin's depocenter may vary with time, such as in active rift basins as extensional faults grow, link or become abandoned.