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 movement. Large faults within the Earths crust result from the action of tectonic forces. Energy release associated with movement on active faults is the cause of most earthquakes. A fault plane is the plane that represents the surface of a fault. A fault trace or fault line is the intersection of a plane with the ground surface. A fault trace is the line commonly plotted on maps to represent a fault. Since faults do not usually consist of a single, clean fracture, the two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the wall occurs above the fault plane. This terminology comes from mining, when working a tabular ore body, because of friction and the rigidity of rocks, they cannot glide or flow past each other easily, and occasionally all movement stops. A fault in ductile rocks can release instantaneously when the rate is too great.
The energy released by instantaneous strain-release causes earthquakes, a common phenomenon along transform boundaries, slip is defined as the relative movement of geological features present on either side of a fault plane, and is a displacement vector. A faults sense of slip is defined as the motion of the rock on each side of the fault with respect to the other side. In practice, it is only possible to find the slip direction of faults. Based on direction of slip, faults can be categorized as, strike-slip. Dip-slip, offset is predominantly vertical and/or perpendicular to the fault trace, oblique-slip, combining significant strike and dip slip. The fault surface is usually vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are known as sinistral faults. Those with right-lateral motion are known as dextral faults
A thrust fault is a type of fault, or break in the Earths crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger, Thrust faults are the result of compressional forces. Thrust faults are a class of reverse faulting that typically have low dip angles. It is often hard to recognize thrusts because their deformation and dislocation can be difficult to detect when they occur within the rocks without appreciable offset of lithological contacts. If the angle of the plane is low and the displacement of the overlying block is large the fault is called an overthrust. Erosion can remove part of the block, creating a fenster when the underlying block is only exposed in a relatively small area. When erosion removes most of the block, leaving only island-like remnants resting on the lower block. If the fault plane terminates before it reaches the Earths surface, because of the lack of surface evidence, blind thrust faults are difficult to detect until they rupture.
The destructive 1994 quake in Northridge, California was caused by a blind thrust fault. Thrust faults, particularly involved in thin-skinned style of deformation, have a so-called ramp-flat geometry. Thrusts mostly propagate along zones of weakness within a sequence, such as mudstones or salt layers. The part of the thrust linking the two flats is known as a ramp and typically forms at an angle of about 15°-30° to the bedding. Continued displacement on a thrust over a ramp produces a characteristic fold geometry known as an anticline or, more generally. Fault-propagation folds form at the tip of a thrust fault where propagation along the decollement has ceased, the continuing displacement is accommodated by formation of an asymmetric anticline-syncline fold pair. As displacement continues the thrust tip starts to propagate along the axis of the syncline, such structures are known as tip-line folds. Eventually the propagating thrust tip may reach another effective decollement layer, when a thrust that has propagated along the lower detachment, known as the floor thrust, cuts up to the upper detachment, known as the roof thrust, it forms a ramp within the stronger layer.
With continued displacement on the thrust, higher stresses are developed in the footwall of the due to the bend on the fault. This may cause renewed propagation along the floor thrust until it again cuts up to join the roof thrust, further displacement takes place via the newly created ramp
Economic geology is concerned with earth materials that can be used for economic and/or industrial purposes. These materials include precious and base metals, nonmetallic minerals, construction-grade stone, petroleum minerals, the term commonly refers to metallic mineral deposits and mineral resources. The techniques employed by other earth science disciplines might all be used to understand, economic geology is studied and practiced by geologists. The purpose of the study of geology is to gain understanding of the genesis. Additionally the fixed stock of most mineral commodities is huge (e. g. copper within the earths crust given current rates of consumption would last for more than 100 million years, economic geologists continue to successfully expand and define known mineral resources. Mineral resources are concentrations of minerals significant for current and future societal needs, Ore is classified as mineralization economically and technically feasible for extraction. Not all mineralization meets these criteria for various reasons, Ore deposits are delineated by mineral exploration, which uses geochemical prospecting and resource estimation via geostatistics to quantify economic ore bodies.
The ultimate aim of process is mining. See main articles Coal and Petroleum geology The study of sedimentology is of importance to the delineation of economic reserves of petroleum. U. S. Geological Survey Circular 831, Principles of a Resource/Reserve Classification for Minerals Dill, the “chessboard” classification scheme of mineral deposits and geology from aluminum to zirconium. Earth-Science Reviews Volume 100, pp. 1–420,2010 Important publications in economic geology Mineral economics Mineral resource classification Ore Ore genesis Coal
Drainage system (geomorphology)
In geomorphology, drainage systems, known as river systems, are the patterns formed by the streams and lakes in a particular drainage basin. They are governed by the topography of the land, whether a region is dominated by hard or soft rocks. Geomorphologists and hydrologists often view streams as being part of drainage basins, a drainage basin is the topographic region from which a stream receives runoff and groundwater flow. The number and shape of the drainage basins found in an area vary and the larger the topographic map, according to the configuration of the channels, drainage systems can fall into one of several categories known as drainage patterns. Drainage patterns depend on the topography and geology of the land, a drainage system is described as accordant if its pattern correlates to the structure and relief of the landscape over which it flows. Dendritic drainage systems are the most common form of drainage system, in a dendritic system, there are many contributing streams, which are joined together into the tributaries of the main river.
They develop where the channel follows the slope of the terrain. Dendritic systems form in V-shaped valleys, as a result, the types must be impervious and non-porous. A parallel drainage system is a pattern of rivers caused by slopes with some relief. Because of the slopes, the streams are swift and straight, with very few tributaries. This system forms on uniformly sloping surfaces, for example, rivers flowing southeast from the Aberdare Mountains in Kenya, parallel drainage patterns form where there is a pronounced slope to the surface. A parallel pattern develops in regions of parallel, elongate landforms like outcropping resistant rock bands, tributary streams tend to stretch out in a parallel-like fashion following the slope of the surface. A parallel pattern sometimes indicates the presence of a fault that cuts across an area of steeply folded bedrock. All forms of transitions can occur between parallel and trellis patterns, the geometry of a trellis drainage system is similar to that of a common garden trellis used to grow vines.
As the river flows along a valley, smaller tributaries feed into it from the steep slopes on the sides of mountains. These tributaries enter the river at approximately 90 degree angle. Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America, rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions of joining at approximately right angles. The joints are less resistant to erosion than the bulk rock so erosion tends to preferentially open the joints
A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere, Continental rifting creates new ocean basins. Eventually the continental rift forms a ridge and the locus of extension moves away from the continent-ocean boundary. The transition between the continental and oceanic lithosphere that was created by rifting is known as a passive margin. Passive margins are found at every ocean and continent boundary that is not marked by a fault or a subduction zone. Passive margins define the region around the Atlantic Ocean, Arctic Ocean, and western Indian Ocean and they are found on the east coast of North America and South America, in western Europe and most of Antarctica. East Asia contains some passive margins and this refers to whether a crustal boundary between oceanic lithosphere and continental lithosphere is a plate boundary or not. Active margins are found on the edge of a continent where subduction occurs and these are often marked by uplift and volcanic mountain belts on the continental plate.
Less often there is a fault, as defines the southern coastline of W. Africa. Most of the eastern Indian Ocean and nearly all of the Pacific Ocean margin are examples of active margins, while a weld between oceanic and continental lithosphere is called a passive margin, it is not an inactive margin. Active subsidence, growth faulting, pore formation and migration are all active processes on passive margins. Passive margins are only passive in that they are not active plate boundaries, Passive margins consist of both onshore coastal plain and offshore continental shelf-slope-rise triads. Coastal plains are dominated by fluvial processes, while the continental shelf is dominated by deltaic. The great rivers drain across passive margins, extensive estuaries are common on mature passive margins. Although there are kinds of passive margins, the morphologies of most passive margins are remarkably similar. Typically they consist of a shelf, continental slope, continental rise. The morphological expression of features are largely defined by the underlying transitional crust.
Passive margins defined by a fluvial sediment budget and those dominated by coral
Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the crust or lithosphere. In the early stages of strike-slip fault formation, displacement within basement rocks produces characteristic fault structures within the overlying cover and this will be the case where an active strike-slip zone lies within an area of continuing sedimentation. At low levels of strain the overall simple shear causes a set of faults to form. The dominant set, known as R shears, form at about 15° to the fault with the same shear sense. The R shears are linked by a set, the R shear that form at about 75° to the main fault trace. The somewhat oblique segments will link downwards into the fault at the base of the sequence with a helicoidal geometry. In detail many strike-slip faults at surface consist of en echelon and/or braided segments in many cases probably inherited from previously formed Riedel shears, in cross-section the displacements are dominantly reverse or normal in type depending on whether the overall fault geometry is transpressional or transtensional.
As the faults tend to join downwards onto a strand in basement. Fault zones with dominantly reverse faulting are known as positive flowers, the identification of such structures, particularly where positive and negative flowers are developed on different segments of the same fault, are regarded as reliable indicators of strike-slip. Strike slip duplexes occur at the step over regions of faults and these occur between two or more large bounding faults which usually have large displacement. An idealized strike-slip fault runs in a line with a vertical dip and has only horizontal motion. In reality, as strike slip faults become large and developed, a long strike slip fault follows a staircase-like trajectory consisting of interspaced fault planes that follow the main fault direction. These sub parallel stretches are isolated by offsets at first, in long stretches of strike-slip the fault plane can start to curve, giving rise to structures similar to step overs. Right lateral motion of a slip fault at a right step over gives rise to extensional bends characterised by zones of subsidence, local normal faults.
On extensional duplexes, normal faults will accommodate the vertical motion, left stepping at a dextral fault generates contractional bends, shortening the step overs which is displayed by local reverse faults, push-up zones, and folds. On contractional duplex structures, thrust faults will accommodate vertical displacement rather than being folded, strike slip dulexes are passive structures, they form as a response to displacement of the bounding fault rather than by the stresses from plate motion. Each horse has a length that varies from half to twice the spacing between the bounding fault planes, because the motion of the duplexes may be heterogeneous, the individual horses can experience a rotation with a horizontal axis, which results in the formation of scissor faults. Scissor faults exhibit normal motion at one end of the horse, an example of strike slip duplexes were observed in the Lambertville sill, New Jersey
Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions.
There are several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians and Ionians, each with their own defining and distinctive dialects.
Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
San Andreas Fault
The San Andreas Fault is a continental transform fault that extends roughly 800 miles through California. It forms the boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip. The fault was first identified in 1895 by Professor Andrew Lawson of UC Berkeley and it is often described as having been named after San Andreas Lake, a small body of water that was formed in a valley between the two plates. However, according to some of his reports from 1895 and 1908, following the 1906 San Francisco earthquake, Lawson concluded that the fault extended all the way into southern California. In 1953, geologist Thomas Dibblee astounded the scientific establishment with his conclusion that hundreds of miles of lateral movement could occur along the fault. A project called the San Andreas Fault Observatory at Depth near Parkfield, Monterey County, is drilling into the fault to improve prediction and this is the approximate location of the epicenter of the 1906 San Francisco earthquake.
The fault returns onshore at Bolinas Lagoon just north of Stinson Beach in Marin County, from Fort Ross the northern segment continues overland, forming in part a linear valley through which the Gualala River flows. It goes back offshore at Point Arena, after that, it runs underwater along the coast until it nears Cape Mendocino, where it begins to bend to the west, terminating at the Mendocino Triple Junction. The central segment of the San Andreas fault runs in a direction from Parkfield to Hollister. The southern segment begins near Bombay Beach, box Canyon, near the Salton Sea, contains upturned strata associated with that section of the fault. The fault runs along the base of the San Bernardino Mountains, crosses through the Cajon Pass. These mountains are a result of movement along the San Andreas Fault and are called the Transverse Range. In Palmdale, a portion of the fault is easily examined at a roadcut for the Antelope Valley Freeway, the fault continues northwest alongside the Elizabeth Lake Road to the town of Elizabeth Lake.
As it passes the towns of Gorman, Tejon Pass and Frazier Park and this restraining bend is thought to be where the fault locks up in Southern California, with an earthquake-recurrence interval of roughly 140–160 years. Northwest of Frazier Park, the runs through the Carrizo Plain. The Elkhorn Scarp defines the fault trace along much of its length within the plain, the southern segment, which stretches from Parkfield in Monterey County all the way to the Salton Sea, is capable of an 8. 1-magnitude earthquake. At its closest, this fault passes about 35 miles to the northeast of Los Angeles. Such a large earthquake on this segment would kill thousands of people in Los Angeles, San Bernardino and surrounding areas
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. A related field that uses geology to infer information regarding past earthquakes is paleoseismology, a recording of earth motion as a function of time is called a seismogram. A seismologist is a scientist who does research in seismology, scholarly interest in earthquakes can be traced back to antiquity. Early speculations on the causes of earthquakes were included in the writings of Thales of Miletus, Anaximenes of Miletus, Aristotle. In 132 CE, Zhang Heng of Chinas Han dynasty designed the first known seismoscope, in 1664, Athanasius Kircher argued that earthquakes were caused by the movement of fire within a system of channels inside the Earth. In 1703, Martin Lister and Nicolas Lemery proposed that earthquakes were caused by chemical explosions within the earth, the Lisbon earthquake of 1755, coinciding with the general flowering of science in Europe, set in motion intensified scientific attempts to understand the behaviour and causation of earthquakes.
The earliest responses include work by John Bevis and John Michell, Michell determined that earthquakes originate within the Earth and were waves of movement caused by shifting masses of rock miles below the surface. From 1857, Robert Mallet laid the foundation of instrumental seismology and he is responsible for coining the word seismology. In 1897, Emil Wiecherts theoretical calculations led him to conclude that the Earths interior consists of a mantle of silicates, surrounding a core of iron. In 1906 Richard Dixon Oldham identified the separate arrival of P-waves, S-waves and surface waves on seismograms, in 1910, after studying the 1906 San Francisco earthquake, Harry Fielding Reid put forward the elastic rebound theory which remains the foundation for modern tectonic studies. The development of this depended on the considerable progress of earlier independent streams of work on the behaviour of elastic materials. In 1926, Harold Jeffreys was the first to claim, based on his study of waves, that below the mantle.
In 1937, Inge Lehmann determined that within the liquid outer core there is a solid inner core. By the 1960s, earth science had developed to the point where a comprehensive theory of the causation of seismic events had come together in the now well-established theory of plate tectonics, seismic waves are elastic waves that propagate in solid or fluid materials. There are two types of waves, Pressure waves or Primary waves and Shear or Secondary waves. S-waves are transverse waves that move perpendicular to the direction of propagation, they appear than P-waves on a seismogram. Fluids cannot support perpendicular motion, so S-waves only travel in solids, the two main surface wave types are Rayleigh waves, which have some compressional motion, and Love waves, which do not. Rayleigh waves result from the interaction of vertically polarized P- and S-waves that satisfy the conditions on the surface
The Glarus thrust is a major thrust fault in the Alps of eastern Switzerland. Along the thrust the Helvetic nappes were thrusted more than 100 km to the north over the external Aarmassif, the thrust forms the contact between older Permo-Triassic rock layers of the Verrucano group and younger Jurassic and Cretaceous limestones and Paleogene flysch and molasse. The Glarus thrust crops out over a large area in the cantons Glarus, St. Gallen and Graubünden, due to its horizontal orientation. Famous outcrops include those at Lochsite near Glarus and in a cliff called Tschingelhörner between Elm and Flims. For this reason the area in which the thrust is found was declared a geotope, the area of this tectonic arena encompasses 32,850 hectares of mainly mountainous landscape in 19 communities between the Surselva and Walensee. In the arena are a number of higher than 3000 meters, such as Surenstock, Ringelspitz. In 2006 the Swiss government made a first proposal to declare the region world heritage to the International Union for Conservation of Nature, the IUCN did not find the area to have an extraordinary or universal value and denied the proposal.
The Swiss made a new, this time successful proposal in March 2008, the American Museum of Natural History in New York exposes a full-scale reconstruction of the Glarus thrust. The first naturalist to examine the Glarus thrust was Hans Conrad Escher von der Linth, Escher von der Linth discovered that, contradictory to Stenos law of superposition, older rocks are on top of younger ones in certain outcrops in Glarus. His son Arnold Escher von der Linth, the first professor in geology at the ETH at Zürich, mapped the structure in more detail and concluded that it could be a huge thrust. At the time, most geologists believed in the theory of geosynclines, Escher von der Linth had therefore difficulty with explaining the size of the thrust fault. In 1848 he invited the British geologist Roderick Murchison, an authority, to come. Murchison was familiar with larger thrust faults in Scotland and agreed with Eschers interpretation, Escher himself felt insecure about his idea and when he published his observations in 1866 he instead interpreted the Glarus thrust as two large overturned narrow anticlines.
This hypothesis was rather absurd, as he admitted himself in private, Eschers successor as professor at Zürich, Albert Heim, initially stuck to his predecessors interpretation of two anticlines. However, some favoured the idea of a thrust. One of them was Marcel Alexandre Bertrand, who interpreted the structure as a thrust in 1884, Bertrand was familiar with the Faille du Midi, a large thrust fault in the Belgian Ardennes. Meanwhile, British geologists began to recognize the nature of thrust faults in the Scottish Highlands, in 1883, Archibald Geikie accepted that the Highlands are a thrust system. At the turn of the century, Heim was convinced of the new theory and he and other Swiss geologists now started mapping the nappes of Switzerland in more detail
In geology, a rift is a linear zone where the Earths crust and lithosphere are being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting, where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the area may contain volcanic rocks, and active volcanism is a part of many. Major rifts occur along the axis of most mid-ocean ridges. Failed rifts are the result of rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a junction where three converging rifts meet over a hotspot. Two of these evolve to the point of spreading, while the third ultimately fails. Most rifts consist of a series of segments that together form the linear zone characteristic of rifts. The individual rift segments have a dominantly half-graben geometry, controlled by a single basin-bounding fault, segment lengths vary between rifts, depending on the elastic thickness of the lithosphere.
Areas of thick colder lithosphere, such as the Baikal Rift have segment lengths in excess of 80 km, while in areas of warmer thin lithosphere, segment lengths may be less than 30 km. Along the axis of the rift the position, and in cases the polarity. Segment boundaries often have a complex structure and generally cross the rift axis at a high angle. These segment boundary zones accommodate the differences in fault displacement between the segments and are known as accommodation zones. Accommodation zones may be located where older crustal structures intersect the rift axis, in the Gulf of Suez rift, the Zaafarana accommodation zone is located where a shear zone in the Arabian-Nubian Shield meets the rift. At the onset of rifting, the part of the lithosphere starts to extend on a series of initially unconnected normal faults. In subaerial rifts, drainage at this stage is generally internal, as the rift evolves, some of the individual fault segments grow, eventually becoming linked together to form the larger bounding faults.
Subsequent extension becomes concentrated on these faults, the longer faults and wider fault spacing leads to more continuous areas of fault-related subsidence along the rift axis. Significant uplift of the rift shoulders develops at this stage, strongly influencing drainage, during rifting, as the crust is thinned, the Earths surface subsides and the Moho becomes correspondingly raised
The theoretical model builds on the concept of continental drift developed during the first few decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s, the lithosphere, which is the rigid outermost shell of a planet, is broken up into tectonic plates. The Earths lithosphere is composed of seven or eight major plates, where the plates meet, their relative motion determines the type of boundary, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually, tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle, the material lost is balanced by the formation of new crust along divergent margins by seafloor spreading.
In this way, the surface of the lithosphere remains the same. This prediction of plate tectonics is referred to as the conveyor belt principle, earlier theories, since disproven, proposed gradual shrinking or gradual expansion of the globe. Tectonic plates are able to move because the Earths lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the ridge and drag, with downward suction. Another explanation lies in the different forces generated by forces of the Sun. The relative importance of each of these factors and their relationship to other is unclear. The outer layers of the Earth are divided into the lithosphere and asthenosphere and this is based on differences in mechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and more rigid, while the asthenosphere is hotter, in terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere transfers heat by convection and has a nearly adiabatic temperature gradient.
The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, Plate motions range up to a typical 10–40 mm/year, to about 160 mm/year. The driving mechanism behind this movement is described below, tectonic lithosphere plates consist of lithospheric mantle overlain by either or both of two types of crustal material, oceanic crust and continental crust. Average oceanic lithosphere is typically 100 km thick, its thickness is a function of its age, as passes, it conductively cools