Types of Faults, Causes, Types, Normal, Reverse, Diagram

Faults in Geology

A fault is a zone of fractures or a fracture between two blocks of rock. This block movement may be sudden, like an earthquake, or it may be gradual, like creep. The length of a fault can range from a few millimetres to thousands of kilometres. Faults can be as short as a few millimetres or as long as thousands of kilometres.

The majority of faults cause repeated displacements over geologic time. The rock on one side of the fault suddenly slips with respect to the other during an earthquake. The fault surface may be vertical, horizontal, or at any other angle. The plane that symbolises a fault’s fracture surface is known as a fault plane.

Types of Faults

There are three different Types of Faults:

• Dip-Slip Faults – occur at an angle in comparison to the surface of Earth
• Strike-Slip Faults – rocks slide past one another
• Oblique-Slip Faults – combine dip-slip and strike-slip movements

Scientists classify types of faults based on the angle of the fault as it relates to the surface of Earth and the direction of the movement along the fault.

Dip-Slip Faults

A dip-slip fault is one in which one side is inclined higher than the other due to vertical movement. One of two types of stresses on the rock cause a dip-slip fault. A slip is the displacement of adjacent points on two sections of rock, typically on either side of a fault. A dip is the angle of the fault’s incline. Dip-slip faults are classified into two types: normal and reverse faults.

A normal fault moves the footwall, or the side of the rock above the inclined fault, upward. In a normal fault, the other side of the rock is known as the hanging wall, and it moves downward.This is caused by tensional stress, which pulls two sides of a rock apart, causing one side of the rock to move downward.

A trench-like feature with straight, parallel walls is called Graben or Rift Valley.  They are formed when a block of rock drops down between two normal faults. On the other hand, when a block is elevated between two normal faults, a horst is formed.  They have a flat top but steep, straight sides. Horsts and Grabens are very common in the East African Rift Valley.

A reverse fault occurs when the footwall moves downward while the hanging wall moves up. Compressional stress causes a reverse fault by pushing two rock plates toward one another. As a result of the pressure, one side of the rock eventually begins to move above the other. A reverse fault is also known as a thrust fault. The thrust fault is a type of reverse fault with a dip of less than 45 degrees. There is also a chance of a blind thrust fault occurring. A blind thrust fault is a type of fault that does not cause the Earth’s surface to crack, so there is no evidence of the fault’s existence.

Strike-Slip Fault

They are formed when the rock masses slip past one another parallel to the strike. They are also called transcurrent faults. Strike-slip faults are right-lateral or left-lateral. It depends on whether the block on the opposite side of the fault has moved to the right or left from an observer’s point of view. There is a special kind of strike-slip fault that form plate boundaries. They are called transform faults.  For example, the San Andreas Fault is a transform fault between the Pacific and American Plates.

Oblique-Slip Faults

Although many faults have both dip-slip and strike-slip components, one or the other usually dominates the overall movement. Oblique faults are those that experience a significant amount of both. A fault with a vertical offset of 300 metres and a left-lateral offset of 5 metres, for example, would not be considered an oblique fault. A fault with 300 metres of both would, on the other hand.It is critical to understand the type of fault because it reflects the type of tectonic forces acting on a specific area.

Geologists use more sophisticated measurements to analyse the specifics of many faults because they exhibit a combination of dip-slip and strike-slip motion.These are faults where the fault plane is inclined in such a way that one side rides up over the other. These faults are formed due to compressional forces. They are formed when both the blocks along the fracture are moving towards each other.

Types of Faults Terms Associated

Types of Faults Earthquakes & Creeps

Pieces of rock along a fault are constantly moving, though these movements are usually so slow that people don’t notice them. A creep is a slow movement that occurs along a fault and goes unnoticed. Larger movements along a fault, on the other hand, result in a massive release of energy. An earthquake is the name given to this sudden release of energy.

An earthquake occurs when a fault slips suddenly. The sudden slip causes the ground to shake and emits seismic energy waves. The area underground where the sudden slip occurred is known as the focus, and it is from this point that seismic waves emanate.The epicentre is the location on Earth’s surface directly above where the sudden slip occurred. Depending on the magnitude of the earthquake, these seismic waves can cause only minor shaking or significant destruction.

Types of Folds

• A symmetrical fold is one with a vertical axial plane.
• An asymmetrical fold is one with an inclined axial plane.
• The limbs of an isoclinal fold are essentially parallel to each other and thus approximately parallel to the axial plane.
• An overturned fold has a highly inclined axial plane with overturned strata on one limb.
• The axial plane of a recumbent fold is essentially horizontal.

Types of Fault UPSC

A fault is a crack in the Earth’s lithosphere formed by the collision of two pieces of rock. Because rock fragments can move at a fault, earthquakes can occur if the movement pushes those fragments into or past one another. Faults can be found all over the world and can range in length from a few millimetres to thousands of kilometres.

However, many faults are inactive, which means that no earthquakes occur on them. Active faults are those where earthquakes happen. The word fault is derived from the Old French term falte, which means an opening or gap.

A solid understanding of this subject is required to help individuals pass competitive exams. On that note, we have covered this topic exclusively for students preparing for the UPSC and IAS exams.

Other Indian Geography Topics

Other Fundamental Geography Topics

Sharing is caring!