Fault (geology)

Satellite image of a fault in the Taklamakan Desert. The two colorful ridges (at bottom left and top right) used to form a single continuous line, but have been split apart by movement along the fault.

Normal fault in La Herradura Formation, Morro Solar, Peru. The light layer of rock shows the displacement. A second normal fault is at the right.

A fault in Morocco. The fault plane is the steeply leftward-dipping line in the centre of the photo, which is the plane along which the rock layers to the left have slipped downwards, relative to the layers to the right of the fault.

Normal fault and drag folds (eastern flanks of the Bighorn Mountains, Wyoming, USA)

Microfault showing a piercing point (the coin's diameter is 18 mm)

Schematic illustration of the two strike-slip fault types

Normal faults in Spain, between which rock layers have slipped downwards (at photo's centre)

Cross-sectional illustration of normal and reverse dip-slip faults

Salmon-colored fault gouge and associated fault separates two different rock types on the left (dark gray) and right (light gray). From the Gobi of Mongolia.

Inactive fault from Sudbury to Sault Ste. Marie, Northern Ontario, Canada

Planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements.

- Fault (geology)

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Simplified map of Earth's principal tectonic plates, which were mapped in the second half of the 20th century (red arrows indicate direction of movement at plate boundaries)

Plate tectonics

Generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago.

Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale)

Plate motion based on Global Positioning System (GPS) satellite data from NASA JPL. Each red dot is a measuring point and vectors show direction and magnitude of motion.

Detailed map showing the tectonic plates with their movement vectors.

Alfred Wegener in Greenland in the winter of 1912–13.

Global earthquake epicenters, 1963–1998. Most earthquakes occur in narrow belts that correspond to the locations of lithospheric plate boundaries.

A demonstration of magnetic striping. (The darker the color is, the closer it is to normal polarity)

Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries (or faults).

Cracks in rock are a mechanism of brittle deformation in response to stress

Fracture (geology)

$The concentric circles in this sandstone are "plumose" (plume-like) structures that can form during the formation and propagation of a fracture$

$Cartoon examples of common tensile fracture mechanisms in laboratory rock samples. A) Axial stretching: tension is applied far from the crack. B) Hydraulic fracturing: tension or compression is applied far away from the crack and fluid pressure increases, causing tension on the face of the cracks. C) Brazilian disc test: applied compressive loads parallel to the crack cause the sides of the disk to bulge out and tension to occur on the crack faces.$

$Rough surfaces on a piece of fractured granite$

$Shear fracture (blue) under shear loading (black arrows) in rock. Tensile cracks, also referred to as wing cracks (red) grow at an angle from the edges of the shear fracture allowing the shear fracture to propagate by the coalescing of these tensile fractures.$

2D Mohr's diagram showing the different failure criteria for frictional sliding vs faulting. Existing cracks orientated between -α/4 and +α/4 on the Mohr's diagram will slip before a new fault is created on the surface indicated by the yellow star.

$Three dimensional computer model of a fracture and fault network (DFN/DFFN), showing the different geological sets in colours, generated by the DMX Protocol using a combination of probabilistic and deterministic procedures$

A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces.

Graben

The Newark Basin, an early Mesozoic half-graben

Rima Ariadaeus on the Moon is thought to be a graben. The lack of erosion on the Moon makes its structure with two parallel faults and the sunken block in between particularly obvious.

In geology, a graben is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.

Thrust fault

Break in the Earth's crust, across which older rocks are pushed above younger rocks.

The Glencoul Thrust at Aird da Loch, Assynt in Scotland. The irregular grey mass of rock is formed of Archaean or Paleoproterozoic Lewisian gneisses thrust over well-bedded Cambrian quartzite, along the top of the younger unit.

Small thrust fault in the cliffs at Lilstock Bay, Somerset, England; displacement of about 2 m

Diagram of the evolution of a fault-bend fold or 'ramp anticline' above a thrust ramp, the ramp links decollements at the top of the green and yellow layers

Diagram of the evolution of a fault propagation fold

Development of thrust duplex by progressive failure of ramp footwall

Antiformal stack of thrust imbricates proved by drilling, Brooks Range Foothills, Alaska

An example of thin-skinned deformation (thrusting) in Montana. Note that the white Madison Limestone is repeated, with one example in the foreground and another at a higher level to the upper right corner and top of the picture.

A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.

Aseismic creep

In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes.

Horst (geology)

In physical geography and geology, a horst is a raised fault block bounded by normal faults.

Strike and dip

Measurement convention used to describe the orientation, or attitude, of a planar geologic feature.

Strike and dip shown alongside cardinal directions on a horizontal plane. Z: strike line of the red plane, σ: strike angle, F: dip direction, φ: dip angle. The angle of the intersection with the green plane is the red plane's apparent dip in the northward direction

A feature's apparent dip is shown when the exposed face is not aligned to the dip direction

A Brunton Geo Transit, used commonly by geologists for strike and dip measurements

Any planar feature can be described by strike and dip, including sedimentary bedding, fractures, faults, joints, cuestas, igneous dikes and sills, metamorphic foliation and fabric, etc. Observations about a structure's orientation can lead to inferences about certain parts of an area's history, such as movement, deformation, or tectonic activity.

Tectonics

Tectonics are the processes that control the structure and properties of the Earth's crust and its evolution through time.

San Andreas transform fault on the Carrizo Plain

This type of tectonics is found at divergent plate boundaries, in continental rifts, during and after a period of continental collision caused by the lateral spreading of the thickened crust formed, at releasing bends in strike-slip faults, in back-arc basins, and on the continental end of passive margin sequences where a detachment layer is present.

Transform fault

The Southern Alps / Kā Tiritiri o te Moana rise dramatically beside the Alpine Fault on New Zealand's West Coast. About 500 kilometres (300 mi) long; northwest at top.

A transform fault or transform boundary, sometimes called a strike-slip boundary, is a fault along a plate boundary where the motion is predominantly horizontal.

Active fault

An active fault is a fault that is likely to become the source of another earthquake sometime in the future.