Faulting - Forces of Tension - Orogenic Processes - Geography Notes

A fault is a fracture or zone of fracture between two blocks of rock. Faulting occurs when a rock above an inclined fracture plane slides over the rock on the opposite side of the fracture as it slides. This movement may occur rapidly, in the form of an earthquake, or may occur slowly, in the form of creep. Faulting may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between. Faulting is an important concept for the UPSC exam.

Faulting

• Faulting is a geological process by which rocks fracture and undergo displacement due to tectonic forces.
• It results from the Earth's lithospheric plates' movement, leading to stress buildup in the Earth's crust.
• When the stress surpasses the rock's strength, it results in a sudden fracture or break, known as a fault.
• The movement along these faults can lead to earthquakes.
• Faults are formed due to the combined effect of both the compressional and tensional forces, but a tensional force plays a significant role in it.
• Exclusive stress and strains produce fracturing and are usually accompanied by dislocation.
• Such relatively rapid movement produced crustal blocks (Horsts) and rift valleys or depressions (Graben).
• Horsts and Graben are found in association with one another.
• The plane along which the rocks are displaced is called the fault plane.

Diagram Depicting the Faults

Types of Faults

• Normal Fault: It is caused by extensional forces where the Earth's crust is being pulled apart. The hanging wall (the block above the fault plane) moves downward relative to the footwall.
• Reserve Fault (Thrust Fault): Resulting from compressional forces where the Earth's crust is being pushed together. In this case, the hanging wall moves upward relative to the footwall.
• Strike Slip Fault: It is caused by horizontal shearing forces. The blocks on either side of the fault move horizontally past each other with little vertical movement.
• Oblique Fault: It is a combination of vertical and horizontal displacements due to both shearing and compressional or extensional forces.
• Listric Fault: These are curved faults where the fault plane is concave upwards. The fault starts nearly vertically at the surface and becomes more horizontal with depth.
• Blind Fault: These faults do not reach the surface, so their existence is not directly observable at the ground level. They are known primarily through indirect methods, like seismic investigations.
• Transform Fault: A specific type of strike-slip fault that offsets segments of the mid-oceanic ridge. The movement on these faults is horizontal, and they link two segments of a diverging boundary or ridge. An example is the transform fault between the North American and Pacific Plates.

Different Types of Faults

Conclusion

Faulting, as a fundamental geological process, significantly influences the Earth's surface's morphology and plays a crucial role in many geological and geomorphic phenomena. The type of faulting in a region can give insights into the nature of tectonic forces acting on that region. It also plays a significant role in determining the seismic activity and associated hazards in an area.

FAQs

MCQs

Question: Consider the following statements regarding faulting:

1. A fault is a junction between two blocks of rocks.
2. Faulting at times takes the form of an earthquake.

Which of the statement(s) given above is/are not correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Question: In which of the following faults does one rock block override the other?

(a) Normal Faults

(b) Reserve Faults

(c) Step Faults

(d) None of the above