Fault (geology)

Faults are discontinuities in the earth which are the result of differential motion within the crust. The two sides of a fault are defined the hangingwall and footwall, such that the fault always dips away from the hangingwall. Faults can be categorised into three groups:

• Normal faults

where the footwall moves downwards (i.e. towards the centre of the Earth) relative to the hangingwall.

• Reverse (or thrust) faults

where the footwall moves upwards (i.e. away from the centre of the Earth) relative to the hangingwall.

Schematic illustration of normal and reverse faults:

[[Image::Nor_rev.png|Schematic of normal and reverse faults]]

• Strike-slip faults

where the fault surface is vertical and the footwall moves either left or right (with respect to the plane perpendicular to the fault and to the Earth's surface). Strike-slip faults with left-lateral motion are also known as sinistral faults. Those with right-lateral motion are also known as dextral faults.