A fault is a fracture or discontinuity in the Earth’s crust where movement has occurred. It is a result of tectonic forces that cause rocks to break and slide past each other along a fault plane. Faults are an integral part of plate tectonics, which explains the large-scale movements and interactions of Earth’s lithospheric plates.
The Classification of Faults
Faults are classified based on various criteria, including the movement direction, orientation, and the nature of displacement.
1. Based on Movement Direction
a) Dip-Slip Faults
- Dip-slip faults are characterized by vertical movement along the fault plane.
- These faults involve either upward movement (reverse fault) or downward movement (normal fault) of rock blocks.
- Reverse faults occur when the hanging wall moves upward relative to the footwall, typically in regions of compressional stress.
- On the other hand, normal faults occur when the hanging wall moves downward relative to the footwall, commonly associated with regions of tensional stress.
b) Strike-Slip Faults
- Strike-slip faults involve horizontal movement along the fault plane, where rocks slide past each other horizontally.
- This type of fault occurs when tectonic forces cause blocks of rocks to move parallel to the strike (horizontal orientation) of the fault.
- Strike-slip faults are further categorized as either right-lateral or left-lateral, depending on the relative movement of the two blocks when facing the fault.
2. Based on Displacement
a) Transform Faults
- Transform faults are a specific type of strike-slip fault that occurs along plate boundaries.
- These faults connect segments of divergent or convergent plate boundaries and facilitate the horizontal movement of lithospheric plates.
- Transform faults are associated with significant seismic activity and are responsible for the formation of prominent features like the San Andreas Fault in California.
b) Oblique-Slip Faults
- Oblique-slip faults exhibit a combination of vertical and horizontal movement along the fault plane.
- These faults involve both dip-slip and strike-slip components of displacement.
- The movement can be either predominantly vertical with a minor horizontal component (oblique-normal fault) or predominantly horizontal with a minor vertical component (oblique-reverse fault).
3. Based on Fault Length and Scale
a) Major Faults
Major faults are long and prominent fractures in the Earth’s crust that extend over significant distances. These faults are often associated with plate boundaries and can have a regional or even continental scale. Examples : the San Andreas Fault in California, the Alpine Fault in New Zealand.
Classification of Faults
Read Also: Types of Block Mountains
