Geologic fault

Geologic fault is a planar fracture or discontinuity in a volume of Earth's crust, which has been subjected to significant displacement as a result of rock-mass 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 the San Andreas Fault in California or the Great Rift Valley in Africa. Faults 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 energy release associated with rapid movement on active faults is the cause of most earthquakes.

Types of Faults

Faults are classified by their direction of movement. The major types include:

• Normal faults occur where the crust is extended. They are identified by the hanging wall moving down relative to the footwall.
• Reverse faults (or thrust faults) occur in areas undergoing compression, where the hanging wall moves up relative to the footwall.
• Strike-slip faults are characterized by the displacement of the Earth's crust predominantly in a horizontal direction, parallel to the fault plane's strike.

Formation

Faults are formed by the tectonic forces which exert different types of stress on the Earth's crust, causing it to crack and slip. Faulting occurs when the stress exceeds the rocks' strength, leading to a fracture and the displacement of the Earth's crust.

Significance

Faults are significant for several reasons:

• They can create significant geological features, including mountain ranges, valleys, and basins.
• They are the main source of earthquakes, making the study of faults crucial for earthquake prediction and understanding seismic hazards.
• Faults affect groundwater flow and the distribution of minerals, influencing the location of resources such as water and petroleum.

Studying Faults

Geologists study faults to understand their mechanics, history, and potential impact on human activities. This involves mapping faults, analyzing the age and rate of movements, and assessing the risks associated with active faults.

See Also

• Earthquake
• Plate tectonics
• Seismology
• Volcano