Editing Alpine Fault (section)

== 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.<ref>{{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}}</ref> 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}}±&nbsp;0.1.<ref name="Howarth2018"/> There is also fair evidence for a post 1717 event confined to North Westland section of the fault but the date is unclear.<ref name="Howarth2018"/> There are two modes of large earthquake behaviour with either major (M<sub>W</sub> 7–8) or great (M<sub>W</sub> > 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.<ref name="Howarth2021">{{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}}</ref>

=== Prehistoric ===
[[New Zealand archaeology|Māori arrived]] in New Zealand about 1300 but never reached a high population density in the colder South Island.<ref>{{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}}</ref> Therefore, while earthquakes are an important part of [[Māori people|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.<ref name="gns">{{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}}</ref> These had separation of between 100 and 350 years.<ref name="gns"/> 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.<ref>{{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}}</ref> 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, New Zealand|Haast]] towards the centre of the fault only identified three major rupture events in the last 1000 years.<ref name="Berryman2012">{{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|url-access= subscription }}</ref> 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.<ref name="Cochran2017"/>
This information has been updated with better dating techniques and is summarised in the following timeline for the various sections of the fault.<ref name="Howarth2018"/>
{{align|center|<timeline>
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"              
 </timeline>}}
This work suggests that large fault ruptures occurred in 1717, about 1400, about 1100 and about 390 CE.<ref name="Howarth2018"/>

=== 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}}<ref group=lower-alpha name="lengthnotes"/> long<ref name="Berryman2012"/> fault was remarkably consistent, rupturing on average every 330 years, at intervals ranging from 140 years to 510 years.<ref name="mediacentre">{{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}}</ref> In 2017, GNS researchers revised the figures after they combined updated Hokuri site records with a thousand-year record from another site, 20&nbsp;km away at John O'Groats River, to produce a record of 27 major earthquake events during the 8000-year period.<ref name="Cochran2017"/> This gave a mean recurrence rate of 291 years, plus or minus 23 years,<ref name="Cochran2017"/> 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.<ref name="GNS2017">{{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}}</ref><ref name="Howarth2018"/> A 2021 study estimated the probability of an earthquake occurring before 2068 was 75 percent.<ref name="GNS2021" /><ref name="rnz" />

=== 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.<ref>{{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 (New Zealand)|Department of Conservation]] / GeoEnvironmental Consultants|issn=1171-9834|access-date=14 September 2018}}</ref> 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.<ref>{{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 (website)|Stuff]] |location=New Zealand}}</ref><ref>{{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 (website)|Stuff]] |location=New Zealand}}</ref><ref>{{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}}</ref> District councils along the [[West Coast, New Zealand|West Coast]] and in [[Canterbury, New Zealand|Canterbury]] have commissioned studies and begun preparations for an anticipated large earthquake on the Alpine Fault.<ref>{{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}}</ref><ref>{{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}}</ref> [[File:Earthquake risk zones New Zealand.png|thumb|Earthquake risk zones New Zealand. Until 2011, the lack of historical earthquakes on the Alpine Fault was interpreted as meaning lower risk.]]