![Piqiang Fault, China detail](https://upload.wikimedia.org/wikipedia/commons/4/48/Piqiang_Fault%2C_China_detail.jpg)
In
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
, a fault is a
planar fracture
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
or discontinuity in a volume of
rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
across which there has been significant displacement as a result of rock-mass movements. Large faults within
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's
crust result from the action of
plate tectonic
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
forces, with the largest forming the boundaries between the plates, such as the megathrust faults of
subduction zones
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
or
transform fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
s. Energy release associated with rapid movement on
active fault
An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...
s is the cause of most
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
s. Faults may also displace slowly, by
aseismic creep
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip in ...
.
A ''fault plane'' is the
plane
Plane(s) most often refers to:
* Aero- or airplane, a powered, fixed-wing aircraft
* Plane (geometry), a flat, 2-dimensional surface
Plane or planes may also refer to:
Biology
* Plane (tree) or ''Platanus'', wetland native plant
* Planes (gen ...
that represents the fracture surface of a fault. A ''
fault trace
A fault trace describes the intersection of a geological fault with the Earth's surface, which leaves a visible disturbance on the surface, usually looking like a crack in the surface with jagged rock structures protruding outward. The term also ...
'' or ''fault line'' is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on
geologic map
A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with st ...
s to represent a fault.
A ''fault zone'' is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed.
Mechanisms of faulting
![Falla normal Morro Solar Peru](https://upload.wikimedia.org/wikipedia/commons/2/2c/Falla_normal_Morro_Solar_Peru.jpg)
Owing to
friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along a fault plane, where it becomes locked, are called ''
asperities
In materials science, asperity, defined as "unevenness of surface, roughness, ruggedness" (from the Latin ''asper''—"rough"), has implications (for example) in physics and seismology. Smooth surfaces, even those polished to a mirror finish, ar ...
''.
Stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
builds up when a fault is locked, and when it reaches a level that exceeds the
strength
Strength may refer to:
Physical strength
*Physical strength, as in people or animals
*Hysterical strength, extreme strength occurring when people are in life-and-death situations
*Superhuman strength, great physical strength far above human ca ...
threshold, the fault ruptures and the accumulated
strain energy
In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) force is called strain energy. For Linear elasticity, linearly elastic materials, strain energy is:
: U = \frac 1 2 V \sigma \epsilon = \frac ...
is released in part as
seismic wave
A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. S ...
s, forming an
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
.
Strain occurs accumulatively or instantaneously, depending on the
liquid state
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, an ...
of the rock; the
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
lower crust and
mantle
A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that.
Mantle may refer to:
*Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear
**Mantle (vesture), an Eastern Orthodox ve ...
accumulate deformation gradually via
shearing
Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (a sheep may be said to have been "shorn" or ...
, whereas the brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when the strain rate is too great.
Slip, heave, throw
![Fault in Seppap Gorge Morocco](https://upload.wikimedia.org/wikipedia/commons/3/33/Fault_in_Seppap_Gorge_Morocco.jpg)
''Slip'' is defined as the relative movement of geological features present on either side of a fault plane. A fault's ''sense of slip'' is defined as the relative motion of the rock on each side of the fault concerning the other side. In measuring the horizontal or vertical separation, the ''throw'' of the fault is the vertical component of the separation and the ''heave'' of the fault is the horizontal component, as in "Throw up and heave out".
![Microfault](https://upload.wikimedia.org/wikipedia/commons/5/53/Microfault.jpg)
The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of the fault (called a
piercing point
In geology, a piercing point is defined as a feature (usually a geologic feature, preferably a linear feature) that is cut by a fault, then moved apart. Reconfiguring the piercing point back in its original position is the primary way geologists ...
). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector.
Hanging wall and footwall
The two sides of a non-vertical fault are known as the ''hanging wall'' and ''footwall''. The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular
ore
Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April 2 ...
body, the miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of the fault movement.
Fault types
Faults are mainly classified in terms of the angle that the fault plane makes with the earth's surface, known as the
dip, and the direction of slip along the fault plane.
Based on the direction of slip, faults can be categorized as:
* ''strike-slip'', where the offset is predominantly horizontal, parallel to the fault trace;
* ''dip-slip'', offset is predominantly vertical and/or perpendicular to the fault trace; or
* ''oblique-slip'', combining strike-slip and dip-slip.
Strike-slip faults
![strike slip fault](https://upload.wikimedia.org/wikipedia/commons/b/bb/Strike_slip_fault.png)
In a strike-slip fault (also known as a ''wrench fault'', ''tear fault'' or ''transcurrent fault''), the fault surface (plane) is usually near vertical, and the footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as ''sinistral'' faults and those with right-lateral motion as ''dextral'' faults. Each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault.
A special class of strike-slip fault is the ''
transform fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
'' when it forms a
plate
Plate may refer to:
Cooking
* Plate (dishware), a broad, mainly flat vessel commonly used to serve food
* Plates, tableware, dishes or dishware used for setting a table, serving food and dining
* Plate, the content of such a plate (for example: ...
boundary. This class is related to an offset in a
spreading center
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
, such as a
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
, or, less common, within continental
lithosphere
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
, such as the
Dead Sea Transform
The Dead Sea Transform (DST) fault system, also sometimes referred to as the Dead Sea Rift, is a series of faults that run from the Maras Triple Junction (a junction with the East Anatolian Fault in southeastern Turkey) to the northern end of the ...
in the
Middle East
The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...
or the
Alpine Fault
The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island (c. 480 km) and forms the boundary between the Pacific Plate and the Indo-Australian Plate. The Southern Alps have been uplifted on the fa ...
in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed.
Dip-slip faults
![Normal faults - Arganda del Rey, Madrid, Spain](https://upload.wikimedia.org/wikipedia/commons/0/0e/Normal_faults_-_Arganda_del_Rey%2C_Madrid%2C_Spain.JPG)
Dip-slip faults can be either ''normal'' ("
extensional In any of several fields of study that treat the use of signs — for example, in linguistics, logic, mathematics, semantics, semiotics, and philosophy of language — an extensional context (or transparent context) is a syntactic environment in w ...
") or ''reverse''.
![Nor rev](https://upload.wikimedia.org/wikipedia/commons/2/2c/Nor_rev.png)
In a normal fault, the hanging wall moves downward, relative to the footwall. A downthrown block between two normal faults dipping towards each other is a
graben
In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.
Etymology
''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...
. An upthrown block between two normal faults dipping away from each other is a
horst. The
dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees.
Low-angle normal faults with regional
tectonic
Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...
significance may be designated
detachment fault
A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade me ...
s.
A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. The terminology of "normal" and "reverse" comes from
coal mining
Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
in England, where normal faults are the most common.
A ''
thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
'' has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°.
Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds.
![Thrust with fault bend fold](https://upload.wikimedia.org/wikipedia/commons/7/70/Thrust_with_fault_bend_fold.svg)
Flat segments of thrust fault planes are known as ''flats'', and inclined sections of the thrust are known as ''ramps''. Typically, thrust faults move ''within'' formations by forming flats and climb up sections with ramps.
Fault-bend folds are formed by the movement of the hanging wall over a non-planar fault surface and are found associated with both extensional and thrust faults.
Faults may be reactivated at a later time with the movement in the opposite direction to the original movement (fault inversion). A normal fault may therefore become a reverse fault and vice versa.
Thrust faults form
nappe
In geology, a nappe or thrust sheet is a large sheetlike body of rock (geology), rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision z ...
s and
klippe
350px, Schematic overview of a thrust system. The shaded material is called a window_(geology).html"_;"title="nappe._The_erosional_hole_is_called_a__window_(geology)">window_or_fenster._The_klippe_is_the_isolated_block_of_the_nappe_overlying_aut ...
n in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes.
Oblique-slip faults
![Oblique slip fault](https://upload.wikimedia.org/wikipedia/commons/9/92/Oblique_slip_fault.svg)
A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault. Nearly all faults have some component of both dip-slip and strike-slip; hence, defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within
transtensional and
transpressional regimes, and others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active.
The ''hade'' angle is defined as the
complement
A complement is something that completes something else.
Complement may refer specifically to:
The arts
* Complement (music), an interval that, when added to another, spans an octave
** Aggregate complementation, the separation of pitch-class ...
of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault.
Listric fault
![Rollover](https://upload.wikimedia.org/wikipedia/commons/3/34/Rollover.png)
Listric faults are similar to normal faults but the fault plane curves, the dip being steeper near the surface, then shallower with increased depth. The dip may flatten into a sub-horizontal
décollement
Décollement () is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a deformational structure, resulting in independent styles of deformation in the rocks above and below the fault. They are ass ...
, resulting in a horizontal slip on a horizontal plane. The illustration shows slumping of the hanging wall along a listric fault. Where the hanging wall is absent (such as on a cliff) the footwall may slump in a manner that creates multiple listric faults.
Ring fault
Ring faults, also known as caldera faults, are faults that occur within collapsed volcanic
caldera
A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...
s
and the sites of
bolide
A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a ...
strikes, such as the
Chesapeake Bay impact crater
The Chesapeake Bay impact crater is a buried impact crater, located beneath the mouth of Chesapeake Bay, United States. It was formed by a bolide that struck the eastern shore of North America about 35.5 ± 0.3 million years ago, in the late Eoc ...
. Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by
ring dike
A ring dike or ring dyke is an intrusive igneous body that is circular, oval or arcuate in plan and has steep contacts. While the widths of ring dikes differ, they can be up to several thousand meters. The most commonly accepted method of ring dik ...
s.
Synthetic and antithetic faults
''Synthetic'' and ''antithetic'' are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction. These faults may be accompanied by
rollover anticlines
Rollover anticlines are anticlines related to extensional normal faults. They must be differentiated from fault-propagation folds, which are associated with reverse faults.
A rollover anticline is a syn-depositional structure developed within t ...
(e.g. the
Niger Delta
The Niger Delta is the delta of the Niger River sitting directly on the Gulf of Guinea on the Atlantic Ocean in Nigeria. It is located within nine coastal southern Nigerian states, which include: all six states from the South South geopolitical ...
Structural Style).
Fault rock
![FaultGouge](https://upload.wikimedia.org/wikipedia/commons/1/10/FaultGouge.JPG)
All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any
mineralising fluids. Fault rocks are classified by their
textures and the implied mechanism of deformation. A fault that passes through different levels of the
lithosphere
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of
detachment fault
A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade me ...
s and major
thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
s.
The main types of fault rock include:
*
Cataclasite
Cataclasite is a cohesive granular fault rock. Comminution, also known as cataclasis, is an important process in forming cataclasites. They fall into the category of cataclastic rocks which are formed through faulting or fracturing in the upper ...
– a fault rock which is cohesive with a poorly developed or absent planar
fabric
Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...
, or which is incohesive, characterised by generally angular
clasts
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
and rock fragments in a finer-grained
matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
of similar composition.
** Tectonic or
fault breccia
Fault breccia ( or ; Italian for "breach"), or tectonic breccia, is a breccia (a rock type consisting of angular clasts) that was formed by tectonic forces.
Fault breccia is a tectonite formed by localized zone of brittle deformation (a fault zon ...
– a medium- to coarse-grained cataclasite containing >30% visible fragments.
**
Fault gouge
Fault gouge is a type of fault rock best defined by its grain size. It is found as incohesive fault rock (rock which can be broken into its component granules at the present outcrop, only aided with fingers/pen-knife), with less than 30% clasts ...
– an incohesive,
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
-rich fine- to
ultrafine-grained cataclasite, which may possess a planar fabric and containing <30% visible fragments. Rock clasts may be present
***
Clay smear
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...
- clay-rich fault gouge formed in
sedimentary
Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...
sequences containing clay-rich layers which are strongly deformed and sheared into the fault gouge.
*
Mylonite
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a cl ...
– a fault rock which is cohesive and characterized by a well-developed planar fabric resulting from tectonic reduction of grain size, and commonly containing rounded
porphyroclast 350px, A mylonite showing a number of (rotated) porphyroclasts: a clear red garnet left in the picture while smaller white feldspar porphyroclasts can be found all over. ''Location'': the tectonics, tectonic contact between the wiktionary:autochth ...
s and rock fragments of similar composition to
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s in the matrix
*
Pseudotachylyte
Pseudotachylyte (sometimes written as pseudotachylite) is an extremely fine-grained to glassy, dark, cohesive rock occurring as veinsTrouw, R.A.J., C.W. Passchier, and D.J. Wiersma (2010) ''Atlas of Mylonites- and related microstructures.'' Spring ...
– ultrafine-grained glassy-looking material, usually black and
flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start fir ...
y in appearance, occurring as thin planar
veins
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...
, injection veins or as a matrix to
pseudoconglomerates or
breccia
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.
The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...
s, which infills dilation fractures in the host rock. Pseudotachylyte likely only forms as the result of seismic slip rates and can act as a fault rate indicator on inactive faults.
Impacts on structures and people
In
geotechnical engineering
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
, a fault often forms a
discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
and rock masses in, for example,
tunnel
A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
,
foundation
Foundation may refer to:
* Foundation (nonprofit), a type of charitable organization
** Foundation (United States law), a type of charitable organization in the U.S.
** Private foundation, a charitable organization that, while serving a good cause ...
, or
slope
In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...
construction.
The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing the
seismic
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
shaking and
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...
hazard to infrastructure and people in the vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the
Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess a fault's age by studying
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
features seen in shallow excavations and
geomorphology
Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...
seen in aerial photographs. Subsurface clues include shears and their relationships to
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
nodules
Nodule may refer to:
*Nodule (geology), a small rock or mineral cluster
*Manganese nodule, a metallic concretion found on the seafloor
*Nodule (medicine), a small aggregation of cells
*Root nodule
Root nodules are found on the roots of plants, p ...
,
eroded
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...
clay, and
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
mineralization, in the case of older soil, and lack of such signs in the case of younger soil.
Radiocarbon dating
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
The method was dev ...
of
organic
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
material buried next to or over a fault shear is often critical in distinguishing active from inactive faults. From such relationships,
paleoseismologists can estimate the sizes of past
earthquakes
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
over the past several hundred years, and develop rough projections of future fault activity.
Faults and ore deposits
Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits.
An example of a fault hosting valuable
porphyry copper deposit
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of ...
s is northern Chile's
Domeyko Fault The Domeyko Fault ( es, Falla Domeyko) or Precordilleran Fault System is a geological fault located in Northern Chile. The fault is of the strike-slip type and runs parallel to the Andes, the coast and the nearby Atacama Fault. The fault origina ...
with deposits at
Chuquicamata
Chuquicamata ( ; referred to as Chuqui for short) is the largest open pit copper mine in terms of excavated volume in the world. It is located in the north of Chile, just outside Calama, at above sea level. It is northeast of Antofagasta and n ...
,
Collahuasi,
El Abra
El Abra is the name given to an extensive archeological site, located in the valley of the same name. El Abra is situated in the east of the municipality Zipaquirá extending to the westernmost part of Tocancipá in the department of Cundinamarc ...
,
El Salvador
El Salvador (; , meaning " The Saviour"), officially the Republic of El Salvador ( es, República de El Salvador), is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south b ...
,
La Escondida and
Potrerillos.
Further south in Chile
Los Bronces
LOS, or Los, or LoS may refer to:
Science and technology
* Length of stay, the duration of a single episode of hospitalisation
* Level of service, a measure used by traffic engineers
* Level of significance, a measure of statistical significance ...
and
El Teniente
El Teniente ("The Lieutenant") is an underground copper mine located in the Chilean Andes, above mean sea level. It is in the commune of Machalí in Cachapoal Province, Libertador General Bernardo O'Higgins Region, near the company town of ...
porphyry copper deposit lie each at the intersection of two fault systems.
[
Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving the right time for—and type of—]igneous differentiation
In geology, igneous differentiation, or magmatic differentiation, is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement, or eruption. The sequence of (u ...
. At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed.[
]
See also
* Anderson's Theory of Faulting
In geology, a fault is a fracture in the surface of the Earth that occurs when a plane of rocks are under extreme stress and break. No movement of the two planes after the fracture results in a joint as opposed to a fault. Motion cements a fractur ...
* Aseismic creep
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip in ...
*
*
*
*
*
*Paleostress inversion
Paleostress inversion refers to the determination of paleostress history from evidence found in rocks, based on the principle that past tectonic stress should have left traces in the rocks. Such relationships have been discovered from field studi ...
*
*
* Vertical displacement
In tectonics, vertical displacement refers to the shifting of land in a vertical direction, resulting in uplift and subsidence. The displacement of rock layers can provide information on how and why Earth's lithosphere changes throughout geologi ...
– Vertical movement of Earth's crust
References
Other reading
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*
*
*
*
External links
Fault Motion Animations
at IRIS Consortium
IRIS (Incorporated Research Institutions for Seismology) is a university research consortium dedicated to exploring the Earth's interior through the collection and distribution of seismographic data. IRIS programs contribute to scholarly research, ...
Aerial view of the San Andreas fault in the Carrizo Plain, Central California, from "How Earthquakes Happen"
at USGS
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...
LANDSAT image of the San Andreas Fault in southern California, from "What is a Fault?"
at USGS
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...
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Structural geology
Stratigraphy
Faults (geology)
Tectonic landforms
Earth's crust