Fault N Fold

Topics: Structural geology, Plate tectonics, Geology Pages: 6 (1626 words) Published: May 13, 2013
The definition of fold is one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of plastic (that is, permanent) deformation. Causes of folding: Rocks deeply buried→Heated→compressed Meanwhile, the meaning of faults is cracks in rocks across which there has been displacement. Reasons of cracks and fractures: * Earth’s surface temperature is low

* Strain rates is high
* Deformation of the rocks
However, in these fold and fault situations, there are also involve with stress and strain. Strain is results from the applied stress to the rocks which is greater than its internal strength. Stress is force per unit and area include of 3 varieties:

→ compression: results from rocks and any other objects are compressed by forces directed toward one another along the same line. →tension: results from forces acting along the same line but in opposite direction and it tends to lengthen rock layers or pull them apart. → shear: forces act parallel one to another but in opposite directions resulting in deformation by displacement along closely spaced planes.

In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. A fault line is the surface trace of a fault, the line of intersection between the fault plane and the Earth's surface. Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane. The two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the hanging wall occurs above the fault plane and the footwall occurs below the fault. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall hanging above him.


A normal fault occurs when the crust is extended. The hanging wall moves downward, relative to the footwall. A downthrown block between two normal faults dipping towards each other is called a graben. An upthrown block between two normal faults dipping away from each other is called a horst. Low-angle normal faults with regional tectonic significance may be designated detachment faults.

A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. The dip of a reverse fault is relatively steep, greater than 45°.

A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and foot wall) folds. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. * STRIKE – SLIP FAULT

The fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults. Those with right-lateral motion are also known as dextral faults.A special class of strike-slip faults is the transform fault, where such faults form a plate boundary. These are found related to offsets in spreading centers, such as mid-ocean ridges, and less commonly within continental lithosphere.

Normal and reverse( thrust ) fault

Strike slip fault

* Fold occurs when sedimentary strata, are bent as a...
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