Back to Contents


Asthenosphere: The layer or shell of the Earth directly below the lithosphere that behaves as a ductile solid.

Dip: The angle between the horizontal plane and a structural surface (such as a bedding plane, a joint, a fault, foliation, or other planar features).

Fault: A fracture or zone of fractures along which there has been displacement of the sides relative to one another, parallel to the fracture.

Footwall: Of the two sides of a non-vertical fault, the side below the fault plane. It is called the footwall because where inactive faults have been "filled in" with mineral deposits and then mined, this is the side on which miners walk.

Graben: An elongate part of the Earth's crust bounded by faults on its long sides and relatively down-dropped compared to its surroundings.

Hangingwall: Of the two sides of a fault, the side above the fault plane. It is called the hanging wall because where inactive faults have been "filled in" with mineral deposits and then mined, this is the side on which miners can hang their lanterns.

Horst: An elongate block that has been raised relative to its surroundings. Its long sides are bounded by steeply inclined faults that generally dip away from each other.

Hydrocarbon: Any of a class of organic compounds consisting of carbon and hydrogen only such as petroleum and natural gas.

Isostasy: A state of equilibrium, resembling flotation, in which segments of the earth's crust stand at levels determined by their thickness and density. Isostatic equilibrium is attained by flow of material in the mantle

Listric fault: has its dip decreasing with depth.

Lithosphere: The solid outer shell of the Earth, including the crust and uppermost rigid layer of the mantle.

Moho: The Mohorvicic Discontinuity; the boundary surface that separates the Earth's crust from the mantle.

Normal fault: A fault characterized by predominantly vertical displacement in which the hanging walll is moved downward with respect to the footwall of the fault. Generally, this kind of fault is a sign of tectonic extension.

Subsidence: The downwawrd settling of material with little horizontal movement.

Thrust fault:A specific kind of reverse fault in which the dip of the fault is less than 45 degrees over much if not all of its length. It is characterized not so much by vertical displacement, but by horizontal compression. Thrust faults are an obvious sign of compressional tectonics.

Back to Top