Alpine Fault
Alpine Fault | |
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Ma[3] | |
Kaikoura | |
New Zealand geology database (includes faults) |
The Alpine Fault is a
Geographic extent and plate motion
The Pacific Plate and Indo-Australian Plate boundary forms the
Tectonics
The Australian Plate, which is in the process of again separating from the
In the northern section of the fault the transition to the Marlborough Fault System reflects transfer displacement between the mainly
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 a year. This is distributed as 36–39 mm of horizontal and 6–10 mm upwards movement on the fault's plane per year.[5]
At the southern end of the fault there is effectively no uplift component of the Pacific Plate
Geological origin and evolution
Between 25 and 12 million years ago 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.[10] 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 the mountains leading to more erosion.[4] 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
Fault zone geology
The fault zone is exposed at numerous locations along the West Coast,[14] and typically consists of a 10 to 50 m wide fault gouge zone[2] with pervasive hydrothermal alteration. This last is because water penetrates down to up to 6 km (3.7 mi) through hot rock associated with the fault. The water then can arise in hot springs with temperatures of over 50 °C (122 °F) in the fault valley,[15] although the temperature of the water at depth is much more extreme.[16] Most of the movement along the fault occurs in this zone.[5] In outcrop, the fault zone is overlain by mylonites which formed at depth and have been uplifted by the fault.[17]
A structural study[18] of a segment of 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 the southern edge due to transpression. The study discussed the short-lived nature of the releasing bend (on the order of 105 to 106 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.[18]
Earthquakes
There have been no major historical earthquakes on the Alpine Fault. Because of this, during the mid-20th century it was speculated that the Alpine Fault creeps without making large earthquakes.[19] 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 Mw 8.1± 0.1.[2] There is also fair evidence for a post 1717 event confined to North Westland section of the fault but the date is unclear.[2] There are two modes of large earthquake behaviour with either major (MW 7–8) or great (MW > 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.[20]
Prehistoric
The
This work suggests that large fault ruptures occurred in 1717, about 1400, about 1100 and about 390 CE.[2]
Historic
There have been no major earthquakes on the Alpine Fault in historic times; its southern and
- 1929 – Arthur's Pass, estimated magnitude = 7.1
- 1929 – Murchison, estimated magnitude = 7.8
- 1968 – Inangahua, estimated magnitude = 7.1
- 2003 – Fiordland, estimated magnitude = 7.1
- 2009 – Fiordland, estimated magnitude = 7.8
Prediction of next earthquake
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, the up to 800 kilometres (500 mi)[n 1] long[24] fault was remarkably consistent, rupturing on average every 330 years, at intervals ranging from 140 years to 510 years.[25] 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 the 8000-year period.[3] This gave a mean recurrence rate of 291 years, plus or minus 23 years,[3] 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.[26][2]
Projected effects of a rupture
Large ruptures can also trigger earthquakes on the faults continuing north from the Alpine Fault. There is
History of research
In 1940,
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.[35][36]
Richard Norris and Alan Cooper from 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.[37] Originally this regional increase in grade 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.[38]
Deep Fault Drilling Project
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.[39][40] It was a $2.5 million international research project designed to drill 1.3 km to the fault plan in two months.[40] The DFDP was the second project to try to drill an active fault zone and return samples after the San Andreas Fault Observatory at Depth.[40][41] One of the goals of the project was to use the deformed rocks from the fault zone to determine its resistance to stress.[40] Researchers also planned to install long term equipment for measuring pressure, temperature and seismic activity near the fault zone.[40] 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, the United Kingdom, and the United States.[42]
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".[16][43] One of the lead researchers said that it is likely to be globally unique.[44]
See also
Notes
- ^ a b c A former length quoted in the article introduction at 480 km, was noted on article review in May 2023 to be discordant with the length presently quoted in the reference used which is of 600 km. This source, while not an original academic work is an respected source so length was corrected back after further validation as explained in this note. It is quite possible that the reference was updated after the access date of 2018-12-31 or that the 480 km figure is actually the length of off set of the fault, inserted in easy to make error, and indeed the offset constrains the minimum length of the fault. It was further noted that another non academic reference to length of the fault used later in the article claimed a fault length of 850 km. This source, when checked was a press statement on research findings, so not peer-reviewed and is possibly from Nathan 2011 as source. It has been corrected too with context. Berryman's group started using a 800 km figure in their 2012 academic work, which is an increased length from Berryman et al. (1992). This gave a 650km length including the Wairau Fault which many workers do not include in the fault length. There is no evidence yet of full rupture including the Wairau Fault (see article). There is evidence for off shore full length fault rupture however as in the 1717 event. The 800 km length includes the Wairau Fault and assumes the off shore portion ends just south of Fiordland. The length of the fault will depend upon how much if any of the southern off shore portion is included or if the Wairau Fault is added. The GNS New Zealand Active Fault database maps about 520 km of fault on land or if the fault was a straight line end to end about 500 km. The total length of the South Island is about 800km for reference. Academic work on the fault does not always state its total length.
References
- ^ "GNS:New Zealand Active Faults Database". Retrieved 2023-04-29.
- ^ S2CID 134211005.
- ^ ISSN 0012-821X.
- ^ a b c "Alpine Fault / Major Faults in New Zealand / Earthquakes / Science Topics / Learning / Home – GNS Science". www.gns.cri.nz. Retrieved 2023-10-11.
- ^ a b c d e Graham 2015, pp. 120.
- ^ "Research finds Alpine Fault quake more likely in the next 50 years, Our Science, 01 June 2021". www.gns.cri.nz. 1 June 2021. Retrieved 30 March 2024.
- ^ "Alpine Fault: Probability of damaging quake higher than previously thought". www.rnz.co.nz. 20 April 2021. Retrieved 3 December 2021.
- .
- S2CID 128996831.
- ^ ISBN 978-1-877480-00-3.
- ^ ISSN 0191-8141.
- S2CID 53613442.
- ISSN 0016-7606.
- ^ "Alpine Fault virtual field trip". University of Otago department of geology. Retrieved 5 July 2021.
- .
- ^ S2CID 205256017.)
{{cite journal}}
: CS1 maint: numeric names: authors list (link - ^ Graham 2015, pp. 120–121.
- ^ ISSN 0191-8141.
- ^ McLintock, Alexander Hare; Frank Foster Evison, M. A.; Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "Earthquakes and Faults". An encyclopaedia of New Zealand, edited by A. H. McLintock, 1966. Retrieved 2019-01-05.
- S2CID 233304353.
- PMID 25378020.
- ^ a b "Alpine Fault". GNS Science. Retrieved 14 March 2018.
- ^ Booker, Jarrod (24 August 2006). "Deadly alpine quake predicted". The New Zealand Herald. Retrieved 18 January 2015.
- ^ .
- ^ "'Well Behaved' Alpine Fault – experts respond". Science Media Centre. 28 June 2012. Retrieved 14 March 2018.
- ^ "New study says Alpine Fault quake interval shorter than thought: GNS Science". stuff www.stuff.co.nz. 6 March 2017. Retrieved 17 September 2018.
- ISSN 1171-9834. Retrieved 14 September 2018.
- ^ "Videos show devastating impact across South Island if Alpine Fault ruptures". Stuff (Fairfax). 16 May 2018.
- ^ "Thousands to be evacuated, highways blocked for months when Alpine Fault ruptures". Stuff (Fairfax). 26 May 2018.
- ^ "South Island plan for the next Alpine Fault quake". Radio New Zealand. 2018-05-15. Retrieved 2019-01-05.
- ^ "Emergency Response Planning". AF8 (Alpine Fault Magnitude 8). Retrieved 2019-02-06.
- ^ "Buller District Council Lifelines Study (Alpine Fault Earthquake Scenario)" (PDF). www.wcrc.govt.nz. 2006. Archived from the original (PDF) on 2018-02-01.
- ^ .
- ^ Wellman, H. w. (1956). "Structural outline of New Zealand (No. 121)". New Zealand Department of Scientific and Industrial Research, Wellington. 121 (4).
- ^ Carroll, Joanne (1 February 2016). "Scientists hunt for clues about big Alpine Fault quake". Stuff. Retrieved 12 April 2024.
- ^ "The wall that Frank built". New Zealand Geographic. Retrieved 2024-04-12.
- ISSN 0191-8141.
- S2CID 128426863.
- .
- ^ a b c d e "Drilling into an active earthquake fault in New Zealand". phys.org. Retrieved 2019-02-16.
- ISSN 0261-3077. Retrieved 2018-12-31.
- ^ "DEEP FAULT DRILLING PROJECT-2 FAQs / drill probe in Alpine Fault / Media Releases / News and Events / Home – GNS Science". www.gns.cri.nz. Retrieved 2018-12-31.
- ^ "Geothermal discovery on West Coast". Otago Daily Times. 18 May 2017.
- ISSN 1170-0777. Retrieved 2018-12-30.
Sources
- Graham, I. J. (2015). A Continent on the Move: New Zealand Geoscience Revealed. Geoscience Society of New Zealand. ISBN 9781877480478.
- Robinson, R (2003). "Potential earthquake triggering in a complex fault network: the northern South Island, New Zealand". .
- Wells, A.; Yetton, M.T.; Duncan, R.P.; and Stewart, G.H. (1999). Prehistoric dates of the most recent Alpine fault earthquakes, New Zealand. Geology, 27(11), 995–998. (abstract)
Further reading
- Howarth, Jamie D.; Barth, Nicolas C.; Fitzsimons, Sean J.; Richards-Dinger, Keith; Clark, Kate J.; Biasi, Glenn P.; Cochran, Ursula A.; Langridge, Robert M.; Berryman, Kelvin R.; Sutherland, Rupert (2021). "Spatiotemporal clustering of great earthquakes on a transform fault controlled by geometry". Nature Geoscience. 14 (5): 314–320. S2CID 233304353.
External links
- Alpine Fault earthquake talk Archived 2014-08-08 at the Wayback Machine – Otago Regional Council
- Alpine Fault research in the Department of Geology – University of Otago
- Where were New Zealand's largest earthquakes? – GNS Science
- Earthquakes and Tectonics in New Zealand – Nature & Company Limited
- The Next Alpine Fault Earthquake in New Zealand – GNS Science on YouTube
- Deep Fault Drilling Programme