Thrust fault

Thrust fault Qilian Shan

Glencoul Thrust Fault Zone in Scotland 2014

Small thrust North verging

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Fault-propagation fold

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Thrust fault is a type of structural fault in which the fault plane has an angle of less than 45 degrees to the surface of the Earth. This means that the hanging wall moves up and over the footwall. Thrust faults are a result of compressional forces that shorten the crust, making them very common in collision zones where tectonic plates or fragments of the lithosphere move towards each other.

Mechanism

In a thrust fault, the fault plane is inclined to the horizontal, and the block above the fault (the hanging wall) moves up relative to the block below (the footwall). This movement is due to compressional forces that squeeze the crust into a smaller space. Thrust faults can accommodate large amounts of shortening of the crust and are therefore associated with fold and mountain building processes.

Types of Thrust Faults

There are several types of thrust faults, including:

• Blind Thrust Faults: These are thrust faults that do not reach the surface and are therefore not evident from looking at the ground above. They can, however, be detected through seismic activity and have been responsible for some significant earthquakes.
• Low-Angle Thrust Faults: These faults have a shallow dipping angle and are often associated with large scale crustal deformations.
• Reverse Faults: While similar to thrust faults, reverse faults have a steeper angle of more than 45 degrees. They are also a result of compressive forces.

Geological Significance

Thrust faults play a significant role in shaping the Earth's surface. They are responsible for forming mountain ranges, such as the Himalayas, which were formed by the collision of the Indian and Eurasian tectonic plates. Thrust faults can also lead to the formation of earthquakes when the energy stored in the fault is released suddenly.

Examples

Some well-known examples of thrust faulting include the Main Himalayan Thrust, responsible for the uplift of the Himalayan mountain range, and the Lewis Thrust Fault in Montana, USA, which has displaced rocks of Precambrian age over much younger Cretaceous rocks.

Environmental and Human Impact

Thrust faults can have significant environmental and human impacts. They are associated with earthquakes, which can lead to loss of life, damage to infrastructure, and economic losses. Understanding thrust faults and their behavior is crucial for earthquake preparedness and mitigation strategies.