53-567: The Ridge Hill Shelf is a landform that forms part of the foothills of the Darling Scarp , a low escarpment that runs parallel with the west coast in southwest Western Australia . It was formed by coastal erosion of the scarp in the Pleistocene , when the sea level was higher, and the scarp located further west than at present. The action of coastal forces produced sand dunes that subsequently lithified into eolianite , and eroded
106-500: 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 forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults
159-405: 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 of the dip angle; it is the angle between
212-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente 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
265-489: A fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas
318-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
371-587: A forest of Eucalyptus marginata (jarrah) and Corymbia calophylla (marri), with an understorey of Banksia , Casuarina fraseriana and Xylomelum occidentale (woody pear). Some publications identify the Ridge Hill Shelf with the foothills of the scarp, but this is incorrect. The foothills are about 15 kilometres wide, and largely continuous, whereas the Ridge Hill Shelf is no more than 3 kilometres wide and highly discontinuous. Darling Scarp The Darling Scarp , also referred to as
424-427: A hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through the stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in
477-484: 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 (e.g. the Niger Delta Structural Style). 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
530-400: A manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along a decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of
583-421: 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 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
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#1732776834082636-464: 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. 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
689-594: Is 1300 mm along the scarp, declining to the east and north. Often the Bureau of Meteorology identifies different weather for "the hills" in comparison to that of the Swan Coastal Plain . Also, in traditionally hot summers, strong easterly winds travelling across the scarp have presented serious issues for planes using the Perth Airport because of the alignment of the runways. On 2 September 1999,
742-422: Is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near the surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in
795-423: 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 practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of
848-475: Is also a tendency to identify the locations on or to the east of the scarp as being in the " Perth Hills " (or simply "The Hills"). The earliest traverses by British settlers in the Swan River Colony occurred in the 1830s. The best known of these is the expedition of Ensign Robert Dale , who appears to have gone from a point near Guildford , to the south side of Greenmount Hill and up through
901-407: Is built, including sand dunes of Pleistocene age formed during the last glacial period . This area is also a distinct physiographic section of the larger Yilgarn Block province, which in turn is part of the larger West Australian Shield division. The Scarp, like the rest of south west Australia, has a Mediterranean climate, with mild rainy winters and warm dry summers. Average annual rainfall
954-544: 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 when it forms a plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or
1007-573: Is found on granite outcrops. Low woodlands of Banksia grow on sand sheets. Native mammals include the quenda ( Isoodon fusciventer ), chuditch ( Dasyurus geoffroii ), woylie ( Bettongia penicillata ogilbyi ), and brush-tailed phascogale ( Phascogale tapoatafa wambenger ). Quokka ( Setonix brachyurus ) and western ringtail possum ( Pseudocheirus occidentalis ) are often restricted to riparian areas. The Darling escarpment has been exploited for stone quarries , forestry and bauxite mining. Extensive timber railways and timber mills and
1060-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. 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
1113-470: Is part of the Jarrah Forest bioregion. The natural vegetation of the scarp is predominantly jarrah–marri forest , characterised by jarrah ( Eucalyptus marginata ) and marri ( Corymbia calophylla ), with bullich ( Eucalyptus megacarpa ) and blackbutt ( Eucalyptus patens ) in the valleys. The Darling Range ghost gum ( Eucalyptus laeliae ) is endemic to the western slopes of the scarp. Heath
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#17327768340821166-492: Is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering , a fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing
1219-425: Is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace 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 maps to represent a fault. A fault zone is a cluster of parallel faults. However,
1272-762: The Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are the most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to
1325-580: The Darling Range or Darling Ranges , is a low escarpment running north–south to the east of the Swan Coastal Plain and Perth , Western Australia . The escarpment extends generally north of Bindoon , to the south of Pemberton . The adjacent Darling Plateau goes easterly to include Mount Bakewell near York and Mount Saddleback near Boddington . It was named after the Governor of New South Wales , Lieutenant-General Ralph Darling . The feature
1378-617: The Helena Valley . The Darling Scarp originated as the local expression, in the Perth area, of the extensive Darling Fault , a major and ancient geological discontinuity separating the Archaean Yilgarn Craton in the east from the younger Pinjarra Orogen and overlying Phanerozoic Perth Basin to the west. The Darling Fault is exposed for over 1,000 kilometres (620 mi), from the area east of Shark Bay , to
1431-679: The Serpentine National Park , John Forrest National Park and the Greenmount National Park , or were simply known as State Forests (e.g. State Forest No.42). Following a change in 2005, the separate parks have been known as the "Parks of the Darling Range", and take up 23,948 hectares on the scarp. Further in August 2008 the parks were given indigenous names: Fault (geology) In geology ,
1484-418: The ironstone of the scarp, resulting in an iron-rich sandstone with a laterite cap. The iron gives the sandstone a dull purple-brown colour; depending on the extent of iron-enrichment, the sandstone may appear predominantly yellow, predominantly purple-brown, or a mottled combination of the two. The shelf is about 250 feet (76 m) high on average, and is therefore well-drained. It is largely vegetated by
1537-657: The seismic shaking and tsunami 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 Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
1590-548: The "edge" of the scarp are those that sit at its western edge, and in most cases command excellent views of the Swan Coastal Plain : The suburbs near Midland and Kalamunda are often referred to as the Perth Hills . The suburbs to the south of Kalamunda are the locations of the main Perth Metropolitan television station transmission towers. There is also another site at Mount Lennard near Collie that Services
1643-469: The Southwest areas including Bunbury . Also in the late twentieth century, dieback affecting jarrah timber in particular infected large tracts of the forest. Currently only the restriction of vehicle access has proved effective in slowing the spread of this disease. This gained greater acceptance and publicity through the decision to allow Rally Australia to operate along services roads provided that
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1696-403: 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 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
1749-436: The direction of slip, faults can be categorized as: 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
1802-421: The early 2000s, Greenmount National Park and John Forrest National Park were repeatedly burnt by bushfires - in most cases through suspected arson. A network of reserves of crown lands on the escarpment have been connected into a regional park to maintain and conserve parts of the escarpment. In most cases the reserves or parks had individual names prior to being incorporated into the larger park, for example
1855-539: The early to mid-twentieth century numerous rock quarries existed on the edge of the escarpment - visible and affecting both the aesthetics and the environment of the escarpment. In the area where the Helena River emerges from its valley to the sandplain , there are still four quarries evident, despite being unused as quarries for fifty years or more. Mountain and Stathams quarries are now managed as rock climbing locations. There have also been visible quarries on
1908-688: The easternmost limit of the various aquifers present in the Perth Basin sediments, most notably the Southwest Yarragadee Aquifer . The scarp forms a divide between the hypersaline groundwaters typical of the Yilgarn Craton basement from the fresh ground waters of the Perth Basin. Some dams along the scarp are contaminated by seepage of saline water from the granite into the base of the dam's water column and must be periodically flushed to preserve water quality. Also in
1961-456: 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 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
2014-402: 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". 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
2067-576: The fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater . 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 dikes . Synthetic and antithetic are terms used to describe minor faults associated with
2120-401: The fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into the geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in
2173-427: The fault-bend fold diagram. Thrust faults form nappes and klippen 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. 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
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2226-475: The gap. If faults form, imbrication fans or domino faulting may form. 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. A thrust fault 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. A section of
2279-470: The number one engine of a Qantas Boeing 747 , en route from Sydney Airport coming into land on Runway 06/24, struck the runway surface upon landing, due to wind shear caused by rolling winds on the Darling Scarp. In addition, orographic uplift is produced when rain clouds move over the hills, giving higher rainfalls in settlements in the ranges compared with their coastal neighbours. The scarp
2332-500: The original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to the footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other,
2385-412: The right time for—and type of— igneous differentiation . 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. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
2438-481: The scarp in the Gosnells and Herne Hill areas. Legislative restrictions upon such developments were initiated in the late twentieth century to prevent further visible scars on the western face of the scarp. In the late twentieth century, the proving of bauxite deposits correlating to the extensive jarrah forests saw wide-ranging protests against the proposals to mine the forests. Campaign to Save Native Forests
2491-465: The southern coast of Western Australia east of Albany . The location of the scarp must once have coincided with the location of the fault , but the scarp has since eroded about 15 kilometres (9.3 mi) eastwards. The original location of the scarp is indicated in places by an unusual landform known as the Ridge Hill Shelf . The Darling Plateau is covered by lateritic materials that cover
2544-678: The supporting communities existed along the escarpment because of the high quality jarrah forests. In the early twentieth century, most of the main rivers flowing off the escarpment had mainly been used for dams for water supply for metropolitan Perth. The dams on the scarp include: The only free flowing water from the Darling Range in the Peel Region is the Dirk Brook in Keysbrook and the Murray River . The scarp also defines
2597-468: 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. Due to friction 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
2650-534: The underlying geology. The Archaean granites and gneisses of the Yilgarn Craton form the high ground of the Perth Hills and can be observed in road cuts, with good examples in the Mundaring Weir area. The only exposed sediments of the Perth Basin, west of the fault, are of Cenozoic age, and are composed of materials such as sandy limestone , travertine and dune sand on which the city of Perth
2703-460: The vehicles had a thorough wash including the under carriage at the end of each stage. In late 2004, the largest bushfire in the northern Jarrah Forest for at least 100 years created significant issues for the forest as well. As a result of this fire intensity the Government increased the volume of controlled burns along the entire escarpment to reduce the buildup of flammable materials. In
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#17327768340822756-521: Was first recorded as General Darling Range by Charles Fraser , Government Botanist with Captain James Stirling aboard HMS Success in March 1827. Maps from the 1830s show the scarp labelled " General Darlings Range"; this later became Darling Range, a name by which the formation was still commonly known in the late 20th century despite common understanding of it being an escarpment. There
2809-479: Was one group to oppose the activity. The lengthy process of protest forced the government and miners to check their original proposals, and wide-ranging processes to guard segments of the jarrah forests from mining ensued. The current mining activity in the region is extensive - the main mines being Huntly and Willowdale. The building and developing of rail access across the scarp developed three separate main routes over eighty years. The localities or suburbs on
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