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50-541: The Ostler Fault Zone (also Ostler Fault ) is an active fault zone, to the east of the Alpine Fault in the Mackenzie District of Canterbury on New Zealand's South Island . It has had multiple recent rupture events greater than M L 6.5 in magnitude, with a recent 6.9 to 7.0 event, and has recently accommodated 1.9 mm (0.075 in)/year of compression and thus land contraction. East of

100-408: A 1 m (3 ft 3 in) slip about 500 years ago, and surface rupture cracks are still present. Larger surface-rupturing earthquakes occurred about 3000, 6000 and 10,000 years ago. A 20 m (66 ft) vertical rupture occurred 18,000 years ago. Contemporary risk is associated with the vertical slip rate of at least 1.1 mm (0.043 in)/year with a recurrence interval of 3000 years and

150-517: A complex splaying of faults, which is associated with large earthquakes adjacent to, but off the Alpine fault itself, such the 1929 Murchison earthquake , 1968 Inangahua earthquake and 1929 Arthur's Pass earthquake . The Alpine Fault has the greatest uplift of the Pacific plate near Aoraki / Mount Cook in its central section. Here the relative motion between the two plates averages 37–40 mm

200-478: A gigabyte of data per minute. The Deep Fault Drilling Project (DFDP) was an attempt in 2014 to retrieve rock and fluid samples and make geophysical measurements inside the Alpine Fault zone at depth. It was a $ 2.5 million international research project designed to drill 1.3 km to the fault plan in two months. The DFDP was the second project to try to drill an active fault zone and return samples after

250-474: A high population density in the colder South Island. Therefore, while earthquakes are an important part of Māori oral tradition, no stories have been passed down about South Island earthquakes. Over the last thousand years, the major ruptures along the Alpine Fault, causing earthquakes of about magnitude 8 had previously been determined to have occurred at least four times. These had separation of between 100 and 350 years. The 1717 quake appeared to have involved

300-546: A rupture along nearly 400 kilometres (250 mi) of the southern two-thirds of the fault. Scientists say that a similar earthquake could happen at any time, as the interval since 1717 is longer than the intervals between the earlier events. Newer research carried out by the University of Otago , the Australian Nuclear Science and Technology Organisation and others has revised the dates and nature of

350-469: A year. This is distributed as 36–39 mm of horizontal and 6–10 mm upwards movement on the fault's plane per year. At the southern end of the fault there is effectively no uplift component of the Pacific plate and other faults share the strain as a result of the plate collision. These include in Fiordland faults associated with the 2003 Fiordland earthquake and 2009 Dusky Sound earthquake ,

400-666: Is graywacke . The fault zone was originally, more than 56 million years ago, a normal fault during the Late Cretaceous to Paleocene and was reactivated as a high angle thrust reverse fault in the last 2.4 million years. The surface deformation patterns across the Ostler Fault Zone are up to about 3 km (1.9 mi) wide in the central portion and usually have highly asymmetric anticlinal folding with broad west-tilted fold backlimbs abruptly transitioning to relatively steep and short fold forelimbs adjacent to

450-603: Is a convergent boundary subducting under the North American plate forming the Aleutian Trench and the corresponding Aleutian Islands (see also: Aleutian Arc ). The Pacific plate is almost entirely oceanic crust , but it contains some continental crust in New Zealand, Baja California , and coastal California . The Pacific plate has the distinction of showing one of the largest areal sections of

500-887: Is a divergent boundary with the Nazca plate forming the East Pacific Rise . The southern side is a divergent boundary with the Antarctic plate forming the Pacific–Antarctic Ridge . The western side is bounded by the Okhotsk microplate at the Kuril–Kamchatka Trench and the Japan Trench . The plate forms a convergent boundary by subducting under the Philippine Sea plate creating

550-450: Is also fair evidence for a post 1717 event confined to North Westland section of the fault but the date is unclear. There are two modes of large earthquake behaviour with either major (M W  7–8) or great (M W  > 8) earthquakes and predicting the next mode is a challenge as these appear to evolve over multiple seismic cycles in response to along-strike differences in geometry. Māori arrived in New Zealand about 1300 but never reached

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600-532: Is in the process of again separating from the Indo-Australian plate , is subducting towards the east south of the South Island and the Pacific plate is subducting towards the west to the north. In the middle, the Alpine Fault is a transform boundary and has both dextral (right-lateral) strike-slip movement and uplift on the southeastern side. The uplift is due to an element of convergence between

650-408: Is summarised in the following timeline for the various sections of the fault. This work suggests that large fault ruptures occurred in 1717, about 1400, about 1100 and about 390 CE. In 2012, GNS Science researchers published an 8000-year timeline of 24 major earthquakes on the (southern end of the) fault from sediments at Hokuri Creek, near Lake McKerrow in north Fiordland. In earthquake terms,

700-610: The Canterbury Plains . The Alpine Fault is not a single structure but often splits into pure strike-slip and dip-slip components. Near the surface, the fault can have multiple rupture zones. The fault zone is exposed at numerous locations along the West Coast, and typically consists of a 10 to 50 m wide fault gouge zone with pervasive hydrothermal alteration. This last is because water penetrates down to up to 6 km (3.7 mi) through hot rock associated with

750-887: The Hawaiian Islands . The north-eastern side is a divergent boundary with the Explorer plate , the Juan de Fuca plate and the Gorda plate forming respectively the Explorer Ridge , the Juan de Fuca Ridge and the Gorda Ridge . In the middle of the eastern side is a transform boundary with the North American plate along the San Andreas Fault , and a boundary with the Cocos plate . The south-eastern side

800-716: The Mariana Trench , has a transform boundary with the Caroline plate , and has a collision boundary with the North Bismarck plate . In the south-west, the Pacific plate has a complex but generally convergent boundary with the Indo-Australian plate , subducting under it north of New Zealand forming the Tonga Trench and the Kermadec Trench . The Alpine Fault marks a transform boundary between

850-640: The Otago fault system , in Canterbury faults such as the Ostler Fault Zone and those associated with the 7.1 M W Darfield earthquake . The uplift in this South Westland region of the fault which has a dextral strike-slip rate of about 28 mm (1.1 in)/year is on the Australian plate side of it with meter scale vertical uplift every 290 years odd. Between 25 and 12 million years ago

900-563: The San Andreas Fault Observatory at Depth . One of the goals of the project was to use the deformed rocks from the fault zone to determine its resistance to stress. Researchers also planned to install long term equipment for measuring pressure, temperature and seismic activity near the fault zone. It was led by New Zealand geologists Rupert Sutherland , John Townsend and Virginia Toy and involves an international team from New Zealand, Canada, France, Germany, Japan,

950-472: The South Island of New Zealand . The right-lateral transpressional Alpine Fault along the western aspect of the South Island takes up no more than 80% of this movement. In the central-southern part of the island the remaining compression element is taken up mainly by reverse faults such as those in the Otago fault system and the Ostler Fault Zone. In this region of South Canterbury the basement rock

1000-568: The Southern Alps were associated with a fault line approximately 650 km (400 miles) long. The fault was officially named the Alpine Fault in 1942 as an extension of a previously mapped structure. At the same time, Harold Wellman proposed the 480 kilometres (300 mi) lateral displacement on the Alpine Fault. This displacement was inferred by Wellman due in part to the similarity of rocks in Southland and Nelson on either side of

1050-618: The Southern Alps , are a number of relatively dry intermontane basins of which the most northern and largest is the Mackenzie Basin (Te Manahuna, the Mackenzie Country). This has been extensively developed for hydroelectric purposes and contains the fault zone which as a result of the risk to power generation has been extensively studied. The fault zone extends from the Ahuriri River in the south to Whale Stream at

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1100-456: The plate tectonics cycle is early- Cretaceous (145 to 137 million years ago). The Pacific plate originated at the triple junction of the three main oceanic plates of Panthalassa , the Farallon , Phoenix , and Izanagi plates , around 190 million years ago. The plate formed because the triple junction had converted to an unstable form surrounded on all sides by transform faults , due to

1150-426: The 8000-year period. This gave a mean recurrence rate of 291 years, plus or minus 23 years, versus the previously estimated rate of 329 years, plus or minus 26 years. In the new study, the interval between earthquakes ranged from 160 to 350 years, and the probability of an earthquake occurring in the 50 years following 2017 was estimated at 29 percent for this southern sector of the fault alone. A 2021 study estimated

1200-527: The Alpine Fault could lead to roads (particularly in or to the West Coast) being blocked for months, as with the 2016 Kaikōura earthquake , with problems in supplying towns and evacuating tourists. District councils along the West Coast and in Canterbury have commissioned studies and begun preparations for an anticipated large earthquake on the Alpine Fault. In 1940, Harold Wellman found that

1250-487: The Alpine Fault to the southwest of Fiordland examined the Dagg Basin, an offshore sedimentary basin at 3,000 m (9,800 ft) depth. Basin sediments are primarily from Pleistocene glaciation , and structures within them reveal a past complexity that is no longer present in the basin. The current structure is a pull-apart basin along a releasing bend in the Alpine Fault, with a segment of inverted basin along

1300-438: The Alpine Fault. Because of this, during the mid-20th century it was speculated that the Alpine Fault creeps without making large earthquakes. However, it is now inferred by multiples lines of evidence that the Alpine Fault ruptures, creating major earthquakes approximately every few hundred years. The last whole fault rupture event was in 1717 and is now known to have been a great earthquake of M w  8.1± 0.1. There

1350-410: The Alpine Fault. Lateral displacements of this magnitude could not be explained by pre-plate tectonics geology and his ideas were not initially widely accepted until 1956. Wellman also proposed in 1964 that the Alpine Fault was a Cenozoic structure, which was in conflict with the older Mesozoic age accepted at the time. This idea coupled with the displacement on the fault proposed that the earth's surface

1400-464: The Department of Geology, University of Otago conducted extensive research on the structure and petrology of the Alpine Fault respectively throughout the later 20th and early 21st centuries. It was during this time that the cyclicity of the Alpine Fault earthquakes and meaning of the increase in metamorphic grade towards the fault was discovered and refined. Originally this regional increase in grade

1450-639: The Southern Alps in the Mackenzie Basin. At depths greater than 300 m (980 ft) the Ostler Fault is a single 45–55° westerly dipping structure, consistent with observations that suggest that the entire Ostler fault has behaved as a kinematically linked array. The fault has been partially characterised down to a depth of 1.5 km (0.93 mi). It is likely that there was a partial rupture that caused debris flow and perhaps up to

1500-533: The United Kingdom, and the United States. In 2017, they reported they had discovered beneath Whataroa , a small township on the Alpine Fault, "extreme" hydrothermal activity which "could be commercially very significant". One of the lead researchers said that it is likely to be globally unique. Pacific plate The plate first came into existence as a microplate 190 million years ago, at

1550-583: The development of a kink in one of the plate boundaries. The "Pacific Triangle", the oldest part of the Pacific plate, created during the initial stages of plate formation, is located just east of the Mariana Trench . The growth of the Pacific plate reduced the Farallon plate to a few remnants along the west coast of the Americas (such as the Juan de Fuca plate ) and the Phoenix plate to a small remnant near

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1600-425: The earthquakes and given greater understanding of their number. Studies at Haast towards the centre of the fault only identified three major rupture events in the last 1000 years. Studies at the far southern end identified seven events in the last 2000 years and the most southern 20 km (12 mi) of the fault has had 27 events since 6000 BCE. This information has been updated with better dating techniques and

1650-404: The fault. The water then can arise in hot springs with temperatures of over 50 °C (122 °F) in the fault valley, although the temperature of the water at depth is much more extreme. Most of the movement along the fault occurs in this zone. In outcrop, the fault zone is overlain by mylonites which formed at depth and have been uplifted by the fault. A structural study of a segment of

1700-797: The island. At this point, it splits into a set of smaller faults known as the Marlborough fault system . This set of faults, which includes the Wairau Fault , the Hope Fault , the Awatere Fault , and the Clarence Fault , transfer displacement between the Alpine Fault and the Hikurangi subduction zone to the north. The Hope Fault is thought to represent the primary continuation of the Alpine Fault. The Australian plate, which

1750-523: The motion on the fault is strike-slip (side to side), with the Tasman district and West Coast moving north and Canterbury and Otago moving south. The average slip rates in the fault's central region are about 38 mm (1.5 in) a year, very fast by global standards. The last major earthquake on the Alpine Fault was in about 1717 AD with a great earthquake magnitude of M w 8.1± 0.1. The probability of another one occurring before 2068

1800-476: The mountains leading to more erosion. This, along with isostatic constraints, has kept the Southern Alps less than 4,000 m (13,000 ft) high. Uplift on the Alpine Fault has led to the exposure of deep metamorphic rocks near the fault within the Southern Alps. This includes mylonites and the Alpine Schist , which increases in metamorphic grade towards the fault. The eroded material has formed

1850-423: The movement on the proto-Alpine Fault was exclusively strike-slip. The Southern Alps had not yet formed and most of New Zealand was covered in water. Then uplift slowly began as the plate motion became slightly oblique to the strike of the Alpine Fault. In the last 12 million years, the Southern Alps have been uplifted approximately 20 km (12 mi), however, as this has occurred more rain has been trapped by

1900-540: The non trivial size of past events. Alpine Fault The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island , being about 600 km (370 mi). long, and forms the boundary between the Pacific plate and the Australian plate . The Southern Alps have been uplifted on the fault over the last 12 million years in a series of earthquakes. However, most of

1950-688: The northern end of Lake Pukaki . The northern part of the fault is on the eastern side of the Ben Ohau Range . The south western uplift from the fault continues in Table Hill to the south of the artificial Lake Ruataniwha , Cloud Hill and the Clay Cliffs of the west side of the Ahuriri River valley. The boundary between the Australian and Pacific plates converges obliquely at about 38 mm (1.5 in)/year in this region of

2000-533: The oldest members of seabed geology being entrenched into eastern Asian oceanic trenches . A geologic map of the Pacific Ocean seabed shows not only the geologic sequences, and associated Ring of Fire zones on the ocean's perimeters, but the various ages of the seafloor in a stairstep fashion, youngest to oldest, the oldest being consumed into the Asian oceanic trenches. The oldest part disappearing by way of

2050-649: The plates, meaning that the fault has a significant high-angle reverse oblique component to its displacement. In the northern section of the fault the transition to the Marlborough Fault System reflects transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary further northwards from the Hikurangi Subduction Zone to the Kermadec Trench . This has resulted in

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2100-418: The probability of an earthquake occurring before 2068 was 75 percent. Large ruptures can also trigger earthquakes on the faults continuing north from the Alpine Fault. There is paleotsunami evidence of near-simultaneous ruptures of the Alpine Fault and Wellington (and/or other major) faults to the north having occurred at least twice in the past 1,000 years. A 2018 study says that a significant rupture in

2150-405: The southern edge due to transpression . The study discussed the short-lived nature of the releasing bend (on the order of 10 to 10 years), during which there were 450 – 1650 m of dextral displacement. The nature of the displacement served as an example of the kinds of ephemeral structures that can develop along a mature strike-slip fault system. There have been no major historical earthquakes on

2200-507: The surface fault traces. These surface manifestations are highly segmented and have been subdivided into three or four primary fault sections and multiple shorter strands due to discontinuities in the surface trace and changes in the overall fault strike. The faults are mainly North–South trending, west-dipping close to pure reverse dip-slip faults that offset a thick sequence of Quaternary glacial outwash and late Neogene lake and stream sediments , up to 1,000 m (3,300 ft) thick, from

2250-556: The triple junction between the Farallon , Phoenix , and Izanagi plates . The Pacific plate subsequently grew to where it underlies most of the Pacific Ocean basin. This reduced the Farallon plate to a few remnants along the west coast of the Americas and the Phoenix plate to a small remnant near the Drake Passage , and destroyed the Izanagi plate by subduction under Asia. The Pacific plate contains an interior hot spot forming

2300-607: The two plates, and further south the Indo-Australian plate subducts under the Pacific plate forming the Puysegur Trench . The southern part of Zealandia , which is to the east of this boundary, is the plate's largest block of continental crust. Hillis and Müller are reported to consider the Bird's Head plate to be moving in unison with the Pacific plate, but Bird considers them to be unconnected. The northern side

2350-404: The up to 800 kilometres (500 mi) long fault was remarkably consistent, rupturing on average every 330 years, at intervals ranging from 140 years to 510 years. In 2017, GNS researchers revised the figures after they combined updated Hokuri site records with a thousand-year record from another site, 20 km away at John O'Groats River, to produce a record of 27 major earthquake events during

2400-482: Was estimated at 75 percent in 2021. The Pacific plate and Indo-Australian plate boundary forms the Macquarie Fault Zone in the Puysegur Trench off the southwestern corner of the South Island and comes onshore as the Alpine Fault just north of Milford Sound. The Alpine Fault then runs the length of the South Island just west of the Southern Alps to near Lewis Pass in the central northern section of

2450-480: Was in relatively rapid constant movement and helped to overthrow the old geosynclinal hypothesis in favour of plate tectonics. In 1964 a 25-metre-long concrete wall was built across the fault to measure the fault's movements and to find if it moves slowly over time or suddenly during big earthquakes. The wall has not moved since being built, which indicates that the build up of energy is released suddenly during large earthquakes. Richard Norris and Alan Cooper from

2500-599: Was inferred to be from frictional heating along the fault not uplift of deeper geological sequences. Richard H. Sibson from the same university also used the Alpine Fault to refine his nomenclature of fault rocks which gained international adherence. Chorus 's dark fibre cables that pass through the Alpine Fault, from the north and south of Haast, are used for distributed acoustic sensing , which detects cable movement produced by earthquakes. Measurements are made using 7,250 'interrogator' locations, spaced four metres apart, which emit and detect pulses of light, generating about

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