Faulting

• Lateral earth movements often produce very great stresses due to compressional forces (when plates move towards one another) and tensional forces (pulling apart).
• These forces can cause fractures or breaks in the earth’s crust.
• When breaks occur in the earth’s crust where no rocks are displaced the breaks are called joints.
• If the rocks are displaced on both or either side of the crack it is called a fault.
• Faulting refers to the fracturing or breaking of the earth’s crust due to both compression and tension forces as a result of the tectonic movements.
• Faulting normally displaces the crustal block along lines.
• The end result is that rocks are either heaved (pushed) above or dropped below the general level of land.

Features of a simple fault

• Heave-the forward horizontal displacement of the sediments.
• Throw-the vertical displacement of the sediments or strata (layer).
• When rocks are folded and tilted they do so in many ways and the following terms are used to describe these tilts.
• Dip-refers to the direction the sediment tilts in.
• Bedding plane-refers to the surface or plane that separates one sediment layer from another. This is normally a line that follows the weaknesses between sediments (layers) of different compositions.

Features of a simple fault.

Types of faults

• There are several types of faults viz:

1. Normal faults
2. Reverse faults.
3. Tear fault

1 Normal faults

A normal fault.

• Is caused by tension forces which cause part of the earth to move downwards.
• That is the central block (the one to the right in the picture, not shown in the picture is a fault plane to the right of the central block) is displaced downwards.

2. Reverse fault.

Reverse fault. Original image by Artinaid.

• Are caused by compressional forces i.e pushing towards each other.
• When rocks are subjected to compression the central block is forced upwards (heaved upwards) relative to the level ground and adjoining blocks.
• That is the central block (the one to the right in the picture) is displaced upwards.

3. The Tear fault.

A tear fault. Image by Artinaid.

• It is produced by tear forces which move in opposite direction of past each other.
• It usually results in rift valleys.

Please go to this page to read on the landforms resulting from faulting.

To access more topics go to the Geography Notes page.