Alpine Fault

{{Infobox fault

| name = Alpine Fault

| other_name =

| named_by =

| year_def =

| image = Zealandia-Continent map en.svg

| image_alt =

| caption = Movement along the Alpine Fault is deforming the continent of Zealandia, with the southern part (on the Pacific plate) sliding past and slightly onto the northwest part (on the Australian plate).

| map_image ={{maplink|frame=yes

|frame-align=center

|text=Map of active Alpine Fault on land (red). Click on the map to enable mouse over of fault features.{{cite web|url=https://data.gns.cri.nz/af/ | title=GNS:New Zealand Active Faults Database|access-date=2023-04-29}}

|raw={{Wikipedia:Map data/Alpine Fault}}

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|frame-height=300

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|frame-long=172.3

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| map_alt =

| pushpin_map =

| pushpin_map_width =

| pushpin_map_caption =

| pushpin_map_alt =

| pushpin_relief = 1

| country = New Zealand

| region = West Coast and Southland regions

| state =

| cities =

| coordinates =

| elevation =

| elevation_ft =

| elevation_ref =

| topdepth_m =

| topdepth_ft =

| topdepth_ref =

| range = Southern Alps

| part_of =

| segments =

| length = {{convert|600|km|mi|abbr=on}}

| width =

| depth =

| strike = NE-SW

| dip =

| dip_angle =

| displacement = {{convert|30|mm|in|abbr=on}}/yr

| plate = Australian, Pacific

| status = Active

| earthquakes = 1717 prehistoric

| type = Strike-slip fault

| movement = Up to {{M|w|8.2|link=y}}, dextral/convergent, east side up

| rockunit =

| age = Miocene-Holocene {{Geological range|12|0.0003|ref=}}

| orogeny = Kaikoura

| volcanic_arc/belt =

| embed = [https://data.gns.cri.nz/geology/ New Zealand geology database (includes faults)]

}}

File:South Island blizzard 2003.jpg formed by the Alpine Fault along the Southern Alps' north-west edge, near the South Island's west coast. This satellite image shows the aftermath of a blizzard that hit the island in July 2003.]]

The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island, being about {{convert|600|km|abbr=on}}.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 650 km 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 [https://data.gns.cri.nz/af/ 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 800 km for reference. Academic work on the fault does not always state its total length. long, and forms the boundary between the Pacific plate and the Australian plate.{{Cite web|url=https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Major-Faults-in-New-Zealand/Alpine-Fault|title=Alpine Fault / Major Faults in New Zealand / Earthquakes / Science Topics / Learning / Home – GNS Science|website=gns.cri.nz|access-date=2023-10-11}} The Southern Alps have been uplifted on the fault over the last 12 million years in a series of earthquakes. However, most of 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 {{convert|38|mm|abbr=on}} a year, very fast by global standards.{{sfn|Graham|2015|p=|pp=120}} The last major earthquake on the Alpine Fault was in about 1717 AD with a great earthquake magnitude of {{M|w|8.1|link=y}}± 0.1. The probability of another one occurring before 2068 was estimated at 75 percent in 2021.{{cite web|url=https://www.gns.cri.nz/news/research-finds-alpine-fault-quake-more-likely-in-the-next-50-years/|title= Research finds Alpine Fault quake more likely in the next 50 years, Our Science, 01 June 2021|date=1 June 2021|website=gns.cri.nz|access-date=30 March 2024}}{{cite web|url=https://www.rnz.co.nz/news/national/440834/alpine-fault-probability-of-damaging-quake-higher-than-previously-thought|title=Alpine Fault: Probability of damaging quake higher than previously thought |website=RNZ |date=20 April 2021 |access-date=3 December 2021}}

Geographic extent and plate motion

File:MarlboroughFaultSystem.png]]

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 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.{{cite journal|last1=Zachariasen|first1=J.|last2=Berryman|first2=K.|last3=Langridge|first3=R.|last4=Prentice|first4=C.|last5=Rymer|first5=M.|last6=Stirling|first6=M.|last7=Villamor|first7=P.|year=2006|title=Timing of late Holocene surface rupture of the Wairau Fault, Marlborough, New Zealand|journal=New Zealand Journal of Geology and Geophysics|volume=49|issue=1 |pages=159–174|doi=10.1080/00288306.2006.9515156|bibcode=2006NZJGG..49..159Z |doi-access=free}}

Tectonics

The Australian plate, which is in the process of again separating from the Indo-Australian plate,{{cite journal |last1=Keep |first1=Myra |last2=Schellart |first2=Wouter P. |title=Introduction to the thematic issue on the evolution and dynamics of the Indo-Australian plate |journal=Australian Journal of Earth Sciences |year=2012 |volume=59, 2012 |issue=6: THEMATIC ISSUE – Evolution and dynamics of the Indo-Australian plate |pages=807–808 |doi=10.1080/08120099.2012.708360 |bibcode=2012AuJES..59..807K |s2cid=128996831 }} 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.{{cite journal|title=Past large earthquakes on the Alpine Fault: paleoseismological progress and future directions|first1=Jamie D. |last1=Howarth |first2= Ursula A. |last2=Cochran |first3= Robert M. |last3=Langridge |first4= Kate |last4=Clark |first5= Sean J. |last5=Fitzsimons |first6=Kelvin |last6=Berryman |first7= Pilar |last7=Villamor |first8=Delia T. |last8=Strong|url= https://www.tandfonline.com/doi/epdf/10.1080/00288306.2018.1464658 |doi= 10.1080/00288306.2018.1464658| year=2018 |volume=61 |issue=3 |pages= 309–328| journal=New Zealand Journal of Geology and Geophysics |bibcode=2018NZJGG..61..309H |s2cid=134211005}} The uplift is due to an element of convergence between the plates, meaning that the fault has a significant high-angle reverse oblique component to its displacement.{{Cite book|url=https://books.google.com/books?id=zjDMNwAACAAJ|title=A Continent on the Move: New Zealand Geoscience into the 21st Century|last=Graham|first=I. J.|date=2008|publisher=Geological Society of New Zealand|isbn=978-1-877480-00-3}}

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 a complex splaying of faults,{{cite journal|last1 =Vermeer|first1 =J.L.|last2 =Quigley|first2 =M.C.|last3 =Duffy|first3 =B.G.|last4 =Langridge|first4 =R.M.|last5 =Pettinga|first5 =J.R.|year =2021|title =Structure and kinematics of active faulting in the Hope-Kelly and Alpine Fault intersection zone, South Island, New Zealand|journal =Tectonophysics|volume =813|at =228928|doi =10.1016/j.tecto.2021.228928|bibcode =2021Tectp.81328928V}} 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.{{efn|Tectonically the faults responsive for the 1929 earthquakes and the 1968 earthquake in Westland and Canterbury are parallel to the Alpine fault and offset from it by about {{cvt|50|km}}.}}

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.{{sfn|Graham|2015|p=|pp=120}}

At the southern end of the fault there is effectively no uplift component of the Pacific plate{{cite journal|first1=Richard J. |last1=Norris |first2= Alan F. |last2=Cooper |title=Late Quaternary slip rates and slip partitioning on the Alpine Fault, New Zealand |journal=Journal of Structural Geology |volume=23 |issue=2–3| date=2001-02-03 |pages=507–520 |issn=0191-8141 |doi=10.1016/S0191-8141(00)00122-X|url=https://www.sciencedirect.com/science/article/pii/S019181410000122X |bibcode=2001JSG....23..507N}} and other faults share the strain as a result of the plate collision.{{cite journal|journal=Earth, Planets and Space |volume =56 |pages=1095–1101|year=2004 |doi=10.1186/BF03353328|last1=Norris |first1= Richard J.|title=Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand |issue =12 |bibcode =2004EP&S...56.1095N |s2cid =53613442 |url=https://link.springer.com/content/pdf/10.1186/BF03353328.pdf |doi-access =free }} These include in Fiordland faults associated with the 2003 Fiordland earthquake and 2009 Dusky Sound earthquake, 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 {{convert|28|mm|abbr=on}}/year is on the Australian plate side of it with meter scale vertical uplift every 290 years odd.{{cite journal|first1=U.A. |last1=Cochran |first2= K.J. |last2=Clark |first3= J.D. |last3=Howarth |first4= G.P. |last4=Biasi |first5= R.M. |last5=Langridge |first6= P. |last6=Villamor |first7= K.R. |last7=Berryman |first8= M.J. |last8=Vandergoes |title=A plate boundary earthquake record from a wetland adjacent to the Alpine fault in New Zealand refines hazard estimates |journal=Earth and Planetary Science Letters |volume =464 |year=2017 |pages=175–188 |issn=0012-821X |doi=10.1016/j.epsl.2017.02.026 |bibcode=2017E&PSL.464..175C |url=https://www.sciencedirect.com/science/article/pii/S0012821X17300948}}

Geological origin and evolution

File:30_ma_New_Zealand_Zealandia.png

File:Alpine Fault Outcrop Hare Waikukupa River New Zealand 02.jpg in green, within the Alpine Fault zone, Waikukupa River.|alt=]]

File:Alpine Fault Outcrop Hare Waikukupa River New Zealand 01.jpg and breccia, Waikukupa River.|alt=]]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. 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 {{convert|20|km|abbr=on}}, however, as this has occurred more rain has been trapped by the mountains leading to more erosion. This, along with isostatic constraints, has kept the Southern Alps less than {{convert|4000|m|abbr=on}} 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 the Canterbury Plains. The Alpine Fault is not a single structure but often splits into pure strike-slip and dip-slip components.{{Cite journal|last1=Cooper|first1=Alan F.|last2=Norris|first2=Richard J.|date=1995-02-01|title=Origin of small-scale segmentation and transpressional thrusting along the Alpine fault, New Zealand|journal=GSA Bulletin|volume=107|issue=2|pages=231–240|doi=10.1130/0016-7606(1995)107<0231:OOSSSA>2.3.CO;2|issn=0016-7606|bibcode=1995GSAB..107..231N}} Near the surface, the fault can have multiple rupture zones.{{sfn|Graham|2015|p=|pp=120}}

Fault zone geology

The fault zone is exposed at numerous locations along the West Coast,{{cite web |title=Alpine Fault virtual field trip |url=https://www.otago.ac.nz/geology/research/alpine-fault/virtual-af.html |publisher=University of Otago department of geology |access-date=5 July 2021}} 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 {{convert|6|km|abbr=on}} through hot rock associated with the fault. The water then can arise in hot springs with temperatures of over {{convert|50|C|abbr=on}} in the fault valley,{{cite journal|last1=Koons |first1= P. O. |year=1987 |title= Some thermal and mechanical consequences of rapid uplift: an example from the Southern Alps, New Zealand. |journal= Earth and Planetary Science Letters |volume=86 |issue= 2–4 |pages= 307–319 |doi=10.1016/0012-821X(87)90228-7 |bibcode= 1987E&PSL..86..307K }} although the temperature of the water at depth is much more extreme.{{cite journal|last1=Sutherland|first1=R.|last2=Townend|first2=J.|last3=Toy|first3=V.|last4=Upton|first4=P. and sixty two others|date=1 June 2017|title=Extreme hydrothermal conditions at an active plate-bounding fault|journal=Nature|volume=546|issue=7656|pages=137–140|doi=10.1038/nature22355|pmid=28514440|url=http://www.escholarship.org/uc/item/5345t6p6|bibcode=2017Natur.546..137S|hdl=1874/351355 |s2cid=205256017|hdl-access=free}} Most of the movement along the fault occurs in this zone.{{sfn|Graham|2015|p=|pp=120}} In outcrop, the fault zone is overlain by mylonites which formed at depth and have been uplifted by the fault.{{sfn|Graham|2015|p=|pp=120–121}}

A structural study{{Cite journal |last1=Barnes |first1=Philip M. |last2=Sutherland |first2=Rupert |last3=Davy |first3=Bryan |last4=Delteil |first4=Jean |date=2001 |title=Rapid creation and destruction of sedimentary basins on mature strike-slip faults: an example from the offshore Alpine Fault, New Zealand |url=http://dx.doi.org/10.1016/s0191-8141(01)00044-x |journal=Journal of Structural Geology |volume=23 |issue=11 |pages=1727–1739 |doi=10.1016/s0191-8141(01)00044-x |bibcode=2001JSG....23.1727B |issn=0191-8141}} of a segment of the Alpine Fault to the southwest of Fiordland examined the Dagg Basin, an offshore sedimentary basin at {{convert|3000|m|abbr=on}} 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 10{{Superscript|5}} to 10{{Superscript|6}} 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.

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.{{Cite web|url=https://teara.govt.nz/en/1966/earthquakes/page-8|title=Earthquakes and Faults|last1=McLintock|first1=Alexander Hare|last2=Frank Foster Evison|first2=M. A.|website=An encyclopaedia of New Zealand, edited by A. H. McLintock, 1966.|access-date=2019-01-05 |last3=Taonga|first3=New Zealand Ministry for Culture and Heritage Te Manatu}} 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 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.{{cite journal | last1=Howarth | first1=Jamie D. | last2=Barth | first2=Nicolas C. | last3=Fitzsimons | first3=Sean J. | last4=Richards-Dinger | first4=Keith | last5=Clark | first5=Kate J. | last6=Biasi | first6=Glenn P. | last7=Cochran | first7=Ursula A. | last8=Langridge | first8=Robert M. | last9=Berryman | first9=Kelvin R. | last10=Sutherland | first10=Rupert | title=Spatiotemporal clustering of great earthquakes on a transform fault controlled by geometry | journal=Nature Geoscience | date=2021 | volume=14 | issue=5 | pages=314–320 | issn=1752-0894 | doi=10.1038/s41561-021-00721-4| bibcode=2021NatGe..14..314H | s2cid=233304353}}

= Prehistoric =

Māori arrived in New Zealand about 1300 but never reached a high population density in the colder South Island.{{Cite journal |last1=Bunce |first1=Michael|last2=Beavan |first2=Nancy R. |last3=Oskam |first3=Charlotte L.|last4=Jacomb|first4=Christopher |last5=Allentoft |first5=Morten E.|last6=Holdaway|first6=Richard N.|date=2014-11-07|title=An extremely low-density human population exterminated New Zealand moa|journal=Nature Communications|volume=5|pages=5436|bibcode=2014NatCo...5.5436H|doi=10.1038/ncomms6436|issn=2041-1723|pmid=25378020|doi-access=free}} 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.{{cite web|url=https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Major-Faults-in-New-Zealand/Alpine-Fault|title=Alpine Fault|website=GNS Science|access-date=14 March 2018}} These had separation of between 100 and 350 years. The 1717 quake appeared to have involved a rupture along nearly {{convert|400|km}} 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.{{cite news | first=Jarrod | last=Booker | url= http://www.nzherald.co.nz/section/story.cfm?c_id=1&ObjectID=10397752 | title=Deadly alpine quake predicted | work=The New Zealand Herald |date=24 August 2006 | access-date=18 January 2015}} 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 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.{{cite journal|last1=Berryman |first1= K.|last2= Cooper |first2= A.F. |last3= Norris |first3= R.J. |last4= Villamor |first4= P.|last5= Sutherland |first5= R.|last6= Wright |first6=T. |last7=Schermer |first7= E.R. |last8= Langridge |first8= R.|last9= Biasi |first9= G. |title= Late Holocene Rupture History of the Alpine Fault in South Westland, New Zealand |journal= Bulletin of the Seismological Society of America |volume=102 |issue=2 |pages=620–638 |year= 2012|url=https://cedar.wwu.edu/cgi/viewcontent.cgi?article=1053&context=geology_facpubs |doi=10.1785/0120110177 |bibcode= 2012BuSSA.102..620B}} Studies at the far southern end identified seven events in the last 2000 years and the most southern {{convert|20|km|abbr=on}} of the fault has had 27 events since 6000 BCE.

This information has been updated with better dating techniques and is summarised in the following timeline for the various sections of the fault.

{{align|center|

ImageSize = width:600 height:106

PlotArea = left:1 bottom:20 top:20 right:100

Alignbars = early

DateFormat = yyyy

Period = from:0 till:2049

TimeAxis = orientation:horizontal format:yyyy order:normal

Colors =

id:O value:black

id:U value:gray(0.90)

id:B value:rgb(0, 1, 1)

id:V value:rgb(1, 0.5, 1)

ScaleMajor = increment:100 start:100

PlotData=

width:10 textcolor:black align:left anchor:from shift:(10,-4)

bar:Header from:400 till:1400 color:white text:"Surface rupturing earthquakes on Alpine Fault during the Common Era"

bar:North from:0 till:1400 color:U

bar:North from:0 till:0 color:U text:" No Data"

bar:North from:1388 till:1407 color:V

bar:North from:1716 till:1718 color:V text:" North Westland"

bar:North from:1728 till:1820 color:V

bar:Central from:0 till:300 color:U

bar:Central from:0 till:0 color:U text:" No Data"

bar:Central from:370 till:416 color:red

bar:Central from:592 till:646 color:red

bar:Central from:915 till:961 color:red

bar:Central from:1008 till:1213 color:red

bar:Central from:1388 till:1407 color:red

bar:Central from:1716 till:1718 color:red text:" Central"

bar:SouthCentral from:20 till:83 color:orange

bar:SouthCentral from:93 till:206 color:orange

bar:SouthCentral from:370 till:416 color:orange

bar:SouthCentral from:592 till:646 color:orange

bar:SouthCentral from:915 till:961 color:orange

bar:SouthCentral from:1008 till:1213 color:orange

bar:SouthCentral from:1388 till:1407 color:orange

bar:SouthCentral from:1716 till:1718 color:orange text:" South Westland"

bar:South from:20 till:83 color:pink

bar:South from:93 till:206 color:pink

bar:South from:370 till:416 color:pink

bar:South from:650 till:739 color:pink

bar:South from:723 till:845 color:pink

bar:South from:1008 till:1213 color:pink

bar:South from:1388 till:1407 color:pink

bar:South from:1716 till:1718 color:pink text:" Near Milford Sound"

bar:OffShore from:93 till:206 color:B

bar:OffShore from:370 till:416 color:B

bar:OffShore from:650 till:739 color:B

bar:OffShore from:723 till:845 color:B

bar:OffShore from:1008 till:1213 color:B

bar:OffShore from:1388 till:1407 color:B

bar:OffShore from:1716 till:1718 color:B text:" Off Shore"

}}

This work suggests that large fault ruptures occurred in 1717, about 1400, about 1100 and about 390 CE.

= 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 {{convert|800|km}} long fault was remarkably consistent, rupturing on average every 330 years, at intervals ranging from 140 years to 510 years.{{cite web|url=http://www.sciencemediacentre.co.nz/2012/06/28/well-behaved-alpine-fault-experts-respond/|title='Well Behaved' Alpine Fault – experts respond|date=28 June 2012|website=Science Media Centre|access-date=14 March 2018}} 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. 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.{{cite web|url=https://www.stuff.co.nz/science/90081709/new-study-says-alpine-fault-quake-interval-shorter-than-thought-gns-science|title=New study says Alpine Fault quake interval shorter than thought: GNS Science|date=6 March 2017|website=stuff www.stuff.co.nz|access-date=17 September 2018}} A 2021 study estimated the probability of an earthquake occurring before 2068 was 75 percent.

= Projected effects of a rupture =

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.{{cite web|url=http://www.doc.govt.nz/documents/science-and-technical/casn333.pdf|title=Catastrophic events in New Zealand coastal environments|last1=Goff|first1=J.R.|last2=Chague-Goff|first2=C.|date=2001|series=Conservation Advisory Science Notes No. 333|publisher=Department of Conservation / GeoEnvironmental Consultants|issn=1171-9834|access-date=14 September 2018}} A 2018 study says that a significant rupture in 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.{{cite web|url=https://www.stuff.co.nz/national/103970504/videos-show-devastating-impact-across-south-island-if-alpine-fault-ruptures|title=Videos show devastating impact across South Island if Alpine Fault ruptures|date=16 May 2018|publisher=Stuff |location=New Zealand}}{{cite web|url=https://www.stuff.co.nz/science/104237236/thousands-to-be-evacuated-highways-blocked-for-months-when-alpine-fault-ruptures|title=Thousands to be evacuated, highways blocked for months when Alpine Fault ruptures|date=26 May 2018|publisher=Stuff |location=New Zealand}}{{Cite web|url=https://www.radionz.co.nz/programmes/news-extras/story/2018644942/south-island-plan-for-the-next-alpine-fault-quake|title=South Island plan for the next Alpine Fault quake|date=2018-05-15|website=Radio New Zealand |access-date=2019-01-05}} District councils along the West Coast and in Canterbury have commissioned studies and begun preparations for an anticipated large earthquake on the Alpine Fault.{{Cite web|url=https://projectaf8.co.nz/safer-framework/emergency-response-planning/|title=Emergency Response Planning|website=AF8 (Alpine Fault Magnitude 8)|access-date=2019-02-06}}{{Cite web|url=https://www.wcrc.govt.nz/Documents/Natural%20Hazards%20and%20Lifelines/Buller%20District%20Council%20Lifelines%20Study.pdf|title=Buller District Council Lifelines Study (Alpine Fault Earthquake Scenario)|date=2006|website=wcrc.govt.nz|archive-url=https://web.archive.org/web/20180201012101/http://www.wcrc.govt.nz/Documents/Natural%20Hazards%20and%20Lifelines/Buller%20District%20Council%20Lifelines%20Study.pdf|archive-date=2018-02-01|url-status=dead}} File:Earthquake risk zones New Zealand.png

History of research

In 1940, Harold Wellman found that the Southern Alps were associated with a fault line approximately 650 km (400 miles) long.{{cite journal|last1=Nathan|first1=S.|date=2011|title=Harold Wellman and the Alpine Fault of New Zealand|url=https://www.researchgate.net/publication/273757760|journal=Episodes|volume=34|issue=1|pages=51–56|doi=10.18814/epiiugs/2011/v34i1/008|doi-access=free|access-date=6 December 2024}} The fault was officially named the Alpine Fault in 1942 as an extension of a previously mapped structure.{{sfn|Graham|2015|p=|pp=120}} At the same time, Harold Wellman proposed the {{convert|480|km|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 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.{{cite journal|last1=Wellman|first1=H. w.|date=1956|title=Structural outline of New Zealand (No. 121)|journal=New Zealand Department of Scientific and Industrial Research, Wellington.|volume=121|issue=4}} 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 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.{{Cite web |last=Carroll |first=Joanne |date=1 February 2016 |title=Scientists hunt for clues about big Alpine Fault quake |url=https://www.stuff.co.nz/national/76403529/scientists-hunt-for-clues-about-big-alpine-fault-quake |access-date=12 April 2024 |publisher=Stuff |location=New Zealand}}{{Cite web |title=The wall that Frank built |url=https://www.nzgeo.com/stories/the-wall-that-frank-built/ |access-date=2024-04-12 |website=New Zealand Geographic}}

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.{{Cite journal|date=2003-12-01|title=Very high strains recorded in mylonites along the Alpine Fault, New Zealand: implications for the deep structure of plate boundary faults|journal=Journal of Structural Geology|volume=25|issue=12|pages=2141–2157|doi=10.1016/S0191-8141(03)00045-2|issn=0191-8141|last1=Norris|first1=Richard J.|last2=Cooper|first2=Alan F.|bibcode=2003JSG....25.2141N }} 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.{{Cite journal|last1=Atkinson|first1=B. K.|last2=White|first2=S. H.|last3=Sibson|first3=R. H.|date=1981-01-01|title=Structure and distribution of fault rocks in the Alpine Fault Zone, New Zealand|url=http://sp.lyellcollection.org/content/9/1/197|journal=Geological Society, London, Special Publications|volume=9|issue=1|pages=197–210|doi=10.1144/GSL.SP.1981.009.01.18|bibcode=1981GSLSP...9..197S |s2cid=128426863|issn=2041-4927}}

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 a gigabyte of data per minute.{{Cite news |date=25 May 2023 |title=Fibre cables offer scientists unprecedented proximity to Alpine Fault seismic zone |url=https://www.rnz.co.nz/news/national/490651/fibre-cables-offer-scientists-unprecedented-proximity-to-alpine-fault-seismic-zone |access-date=27 June 2024 |work=RNZ}}{{Cite news |date=16 June 2023 |title=Seismology at light speed: how fibre-optic telecommunications cables deliver a close-up view of NZ's Alpine Fault |url=https://theconversation.com/seismology-at-light-speed-how-fibre-optic-telecommunications-cables-deliver-a-close-up-view-of-nzs-alpine-fault-206858 |access-date=27 June 2024 |work=The Conversation}}

= 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.{{Cite journal|last=Townend|first=John|date=2009|title=Deep Fault Drilling Project—Alpine Fault, New Zealand|url=https://www.sci-dril.net/8/75/2009/sd-8-75-2009.pdf|journal=Scientific Drilling|volume=8|pages=75–82|doi=10.5194/sd-8-75-2009|bibcode=2009SciDr...8...75T |doi-access=free}}{{Cite web|url=https://phys.org/news/2014-09-drilling-earthquake-fault-zealand.html|title=Drilling into an active earthquake fault in New Zealand|website=phys.org|access-date=2019-02-16}} 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 the San Andreas Fault Observatory at Depth.{{Cite news|url=https://www.theguardian.com/science/2005/dec/10/thisweekssciencequestions.geology|title=Why are scientists drilling into the San Andreas fault?|last=Ravilious|first=Kate|date=2005-12-10|work=The Guardian |access-date=2018-12-31|issn=0261-3077}} 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, the United Kingdom, and the United States.{{Cite web|url=https://www.gns.cri.nz/Home/News-and-Events/Media-Releases/drill-probe-in-Alpine-Fault/DEEP-FAULT-DRILLING-PROJECT-2-FAQs|title=DEEP FAULT DRILLING PROJECT-2 FAQs / drill probe in Alpine Fault / Media Releases / News and Events / Home – GNS Science|website=gns.cri.nz|access-date=2018-12-31}}

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".{{cite web|url=https://www.odt.co.nz/regions/west-coast/geothermal-discovery-west-coast|title=Geothermal discovery on West Coast|date=18 May 2017|website=Otago Daily Times }} One of the lead researchers said that it is likely to be globally unique.{{Cite news|url=https://www.nzherald.co.nz/the-country/news/article.cfm?c_id=16&objectid=11858291|title=Geothermal discovery on West Coast|last=Elder|first=Vaughan|work=The New Zealand Herald |access-date=2018-12-30|issn=1170-0777}}

Notes

References

=Sources=

{{Cite book|url=https://books.google.com/books?id=LIgbjgEACAAJ&q=a+continent+on+the+move|title=A Continent on the Move: New Zealand Geoscience Revealed|last=Graham|first=I. J.|date=2015|publisher=Geoscience Society of New Zealand|isbn=9781877480478}}
{{cite journal | last1 = Robinson | first1 = R | year = 2003 | title = Potential earthquake triggering in a complex fault network: the northern South Island, New Zealand | journal = Geophysical Journal International | volume = 159 | issue = 2| pages = 734–748 | doi = 10.1111/j.1365-246x.2004.02446.x | doi-access = free }}
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. [http://data.gns.cri.nz/bib/abstract.jsp?type=template&id=83344 (abstract)]

External links

[http://www.orc.govt.nz/Information-and-Services/Natural-Hazards/Great-Alpine-Fault-Earthquake/ Alpine Fault earthquake talk] {{Webarchive|url=https://web.archive.org/web/20140808052007/http://www.orc.govt.nz/Information-and-Services/Natural-Hazards/Great-Alpine-Fault-Earthquake/ |date=2014-08-08 }} – Otago Regional Council
[https://www.otago.ac.nz/geology/research/alpine-fault/index.html Alpine Fault research in the Department of Geology] – University of Otago
[http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/New-Zealand-Earthquakes/Where-were-NZs-largest-earthquakes Where were New Zealand's largest earthquakes?] – GNS Science
[https://web.archive.org/web/20080123092242/http://www.natureandco.co.nz/land_and_wildlife/landforms/tectonics/idx_tect.php3 Earthquakes and Tectonics in New Zealand] – Nature & Company Limited
[https://www.youtube.com/watch?v=tfj8MIAxec4&t=385s The Next Alpine Fault Earthquake in New Zealand] – GNS Science on YouTube
[https://www.gns.cri.nz/research-projects/deep-fault-drilling-programme/ Deep Fault Drilling Programme]

Category:Active faults

Category:Seismic faults of New Zealand

Category:Strike-slip faults

Category:Geographic areas of seismological interest

Category:Seismic zones of New Zealand