Genetic classification of fault and joint

Genetic classification groups a structure by the way it was formed (its origin and the nature of the movement or stress).

Genetic classification of faults

By relative movement

1. Normal fault - the hanging wall moves down relative to the foot wall; caused by tension.
2. Reverse fault - the hanging wall moves up relative to the foot wall; caused by compression. A reverse fault with a dip of less than 45 degrees is a thrust fault.
3. Strike-slip (lateral) fault - the blocks move horizontally along the strike of the fault; caused by shearing. It may be right-lateral (dextral) or left-lateral (sinistral).
4. Oblique-slip fault - the movement has both dip-slip and strike-slip components.
5. Rotational (hinge/pivotal) fault - one block rotates about a point on the fault.
6. Horst and graben - a horst is a block raised between two normal faults; a graben is a block dropped between them.

Genetic classification of joints

1. Tension joints - formed by tensile stress (stretching); usually open and irregular.
2. Shear joints - formed by shear stress (usually under compression), in conjugate sets; smooth and closed.
3. Release (unloading) joints - formed when pressure is released after the overburden is removed; for example, sheeting joints.
4. Cooling (contraction) joints - formed in igneous rocks during cooling, such as columnar joints in basalt.
5. Mural joints - cubic joints in granite produced by cooling and unloading.
6. Tectonic joints - related to folding and faulting; longitudinal, transverse or oblique joints.