2021 Kermadec Islands earthquakes

The Kermadec-Tonga subduction zone runs east of the Kermadec Islands and marks the boundary between the Australian and Pacific plates. This convergent boundary is where the denser Pacific plate subducts or dives beneath the less dense Australian plate.{{cite journal|last1=M. J. Funnell, C. Peirce, W. R. Stratford, M. Paulatto, A. B. Watts, I. Grevemeyer|title=Structure and deformation of the Kermadec forearc in response to subduction of the Pacific oceanic plate|journal=Geophysical Journal International|date=2014|volume=199|issue=2|pages=1286–1302|doi=10.1093/gji/ggu330|url=https://academic.oup.com/gji/article/199/2/1286/2874205|access-date=5 March 2021|doi-access=free}}

The main magnitude 8.1 megathrust earthquake occurred at 08:28:31 NZDT on 5 March 2021 (19:28:31 UTC, 4 March) along the subduction zone due to reverse faulting. The USGS estimated that the rupture zone was {{convert|175|by|75|km|abbr=on}} in area. The main shock was preceded by a magnitude 7.4 foreshock less than two hours prior, at 06:41:25 NZDT (17:41:25 UTC).

About 6 hours before the main quake, at 02:27:36 NZDT on 5 March (13:27:36 UTC, 4 March) a magnitude 7.3 earthquake struck {{convert|100|km|abbr=on|sigfig=1}} off East Cape in the North Island.{{cite web|url=https://earthquake.usgs.gov/earthquakes/eventpage/us7000dffl/executive|title=M 7.3 – 174 km NE of Gisborne, New Zealand|publisher=United States Geological Survey|date=4 March 2021|access-date=5 March 2021}} This earthquake was felt largely across the country, and woke many people up, but no damage was caused.{{cite web|url=https://www.geonet.org.nz/earthquake/technical/2021p169083|title=Magnitude 7.3, Fri Mar 5 2021 2:27 AM|publisher=GeoNet|date=5 March 2021|access-date=23 May 2021}} This earthquake was considered an independent event.{{cite news|url=https://www.washingtonpost.com/weather/2021/03/04/earthquake-tsunami-new-zealand-hawaii/|title=Earthquake near New Zealand with Pacific tsunami threat|date=5 March 2021|access-date=5 March 2021|newspaper=The Washington Post|quote=A magnitude 7.3 hit near New Zealand early on Thursday, [...] occurred far enough apart that they likely were not related.}} A tsunami flooding warning was issued due to this quake, which was rescinded before the other quakes hit.{{cite news|url=https://www.stuff.co.nz/national/300245008/earthquake-cluster-and-tsunami-alert-what-you-need-to-know|title=Earthquake cluster and tsunami alert: what you need to know|work=Stuff|date=5 March 2021|access-date=7 March 2021}}

On 28 July 2021, nearly 5 months after the Kermadec Islands mainshock, an 8.2 magnitude earthquake struck the Alaska Peninsula,{{Cite web|date=29 July 2021|title=M 8.2 – 91 km ESE of Perryville, Alaska|url=https://earthquake.usgs.gov/earthquakes/eventpage/ak0219neiszm/executive|publisher=United States Geological Survey|access-date=23 August 2021}} and another 8.1 magnitude earthquake struck the Sub-Antarctic British territory of the South Sandwich Islands on 12 August of that year.{{Cite web|title=M 8.1 – South Sandwich Islands region|url=https://earthquake.usgs.gov/earthquakes/eventpage/us6000f53e/executive|publisher=United States Geological Survey|access-date=23 August 2021}} This is unusual since earthquakes of magnitude 8 or higher occur only about once every year on average.{{cite web|title=How Often Do Earthquakes Occur?|url=https://www.iris.edu/hq/inclass/fact-sheet/how_often_do_earthquakes_occur|publisher=IRIS Consortium|access-date=23 August 2021}} There is no evidence of a causal relationship between the three events. 2021 has had the most 8.0+ earthquakes in a single year since 2007.{{cite web|title=Significant Earthquakes – 2007|url=https://earthquake.usgs.gov/earthquakes/browse/significant.php?year=2007|publisher=United States Geological Survey|access-date=23 August 2021}}

As of 27 January 2023, there have been at least 2,847 aftershocks above 4.0 magnitude,{{Cite web|title=USGS earthquake catalog|url=https://earthquake.usgs.gov/earthquakes/map/?extent=-46.73986,169.45313&extent=-6.48998,197.57813&range=search&timeZone=utc&map=false&search=%7B%22name%22:%22Search%20Results%22,%22params%22:%7B%22starttime%22:%222021-03-04%2000:00:00%22,%22endtime%22:%222030-01-01%2023:59:59%22,%22maxlatitude%22:-22.106,%22minlatitude%22:-34.597,%22maxlongitude%22:191.953,%22minlongitude%22:175.078,%22minmagnitude%22:4,%22orderby%22:%22time%22%7D%7D|publisher=United States Geological Survey}} and 13 of them above magnitude 6. A magnitude 7.1 earthquake struck close to Raoul Island on 24 April 2023, over two years after the mainshock.{{Cite web|date=24 April 2023|title=M 7.1 – Kermadec Islands, New Zealand|url=https://earthquake.usgs.gov/earthquakes/eventpage/us6000k6mg/executive|access-date=21 May 2023|publisher=United States Geological Survey}} It is currently the largest aftershock of the sequence.

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According to GeoNet, the mainshock caused more than 300 landslides on steep forest cliffs and rugged coastal cliffs on Raoul Island. The largest slide was at Pills Beach, where about 400 metres of coastal cliffs collapsed, leaving a column of sediment in the ocean.{{Cite web|title=Earthquake has caused more than 300 landslides on Raoul Island|url=https://exbulletin.com/uncategorized/815345/|website=exbulletin.com|date=26 March 2021}}

A few buildings were damaged in Raoul Island. However, there were no casualties as the island was uninhabited at the time due to the COVID-19 pandemic.{{Cite web|date=4 March 2021|title=No one on Kermadec Islands during earthquakes and tsunami warning|url=https://www.stuff.co.nz/national/nz-earthquake/124444279/no-one-on-kermadec-islands-during-earthquakes-and-tsunami-warning|access-date=4 March 2021|website=Stuff}}

The main quake led to tsunami warnings being issued around the Pacific, as far away as Peru, but particularly for the North Island of New Zealand.{{Cite web|date=4 March 2021|title=Live: 'Try and stay calm' says emergency management minister, tsunami waves expected for 'several hours' after earthquake|url=https://www.stuff.co.nz/national/300245006/live-try-and-stay-calm-says-emergency-management-minister-tsunami-waves-expected-for-several-hours-after-earthquake|access-date=4 March 2021|website=Stuff}}

Thousands of New Zealanders evacuated to higher ground.{{cite news|url=https://www.9news.com.au/world/new-zealand-earthquake-tsunami-warning-powerful-quake-off-northeast-coast/61b590ce-cb0e-4b01-bf34-320ffa183bcc|title=Tsunami threat passes in New Zealand, as evacuees allowed to return|first=Nick|last=Pearson|work=9 News|date=5 March 2021|access-date=5 March 2021}} NEMA said the first waves were due to reach New Zealand at around 9:49 am local time, with flooding expected along areas of the East and West Coasts of the North Island, and issued an evacuation order for areas of Northland, Bay of Plenty, Gisborne, and Great Barrier Island.{{cite news|url=https://www.rnz.co.nz/news/national/437694/major-8-point-1-quake-at-kermadecs-people-told-to-move-to-higher-ground|title=Major 8.1 quake at Kermadecs, people told to move to higher ground|work=Radio New Zealand|date=5 March 2021|access-date=5 March 2021}}

The tsunami land threat was dropped at 1:27 pm NZDT to a "Beach and Marine threat."{{cite web|title=National Emergency Management Agency on Twitter|url=https://twitter.com/NZcivildefence/status/1367632799629414401|via=Twitter}}

While the tsunami heights were initially predicted to be {{Convert|1|–|3|m|ft|abbr=on}} high,{{cite news|url=https://www.nzherald.co.nz/nz/earthquake-swarm-north-island-tsunami-warning-lifted-after-81-shake-evacuees-return-home/OOON3VQ4G75ENH7VASABKYUTBM/|title=Earthquake swarm: North Island tsunami warning lifted after 8.1 shake, evacuees return home|work=The New Zealand Herald|date=5 March 2021|access-date=23 August 2021}} tsunami heights measured by GeoNet ended up being around {{Convert|0.35|–|0.40|m|ft|abbr=on}} at East Cape and around {{Convert|0.15|–|0.20|m|ft|abbr=on}} at Great Barrier Island;{{Cite web|title=GeoNet News|url=https://www.geonet.org.nz/news/2SEHsNpMPFY7LyLkduIPNJ|access-date=5 March 2021|publisher=GeoNet}} {{convert|0.64|m|ft|abbr=on}} waves were reported in Norfolk Island. The tsunami heights at Raoul Island from the main earthquake are estimated to have reached {{Convert|2.4|m|ft|abbr=on}},{{Cite web|title=New Zealand and Pacific island countries – Earthquake|url=https://reliefweb.int/report/new-zealand/new-zealand-and-pacific-island-countries-earthquake-dg-echo-partners-nema-nz-ptwc|publisher=ReliefWeb|date=5 March 2021}} however, exact heights at the island from the main earthquake were not able to be measured because the earthquake destroyed the island's monitoring equipment.{{Cite news|date=11 March 2021|title=Kermadec Islands: Data on second quake lost due to monitoring equipment damage|work=RNZ |url=https://www.rnz.co.nz/news/national/438166/kermadec-islands-data-on-second-quake-lost-due-to-monitoring-equipment-damage|access-date=1 November 2021}} In Port-Vila, Vanuatu, a few boats were damaged and several people were injured.{{Better source needed|date=October 2021}}

{{Portal|Earth sciences|New Zealand}}

• List of earthquakes in 2021
• List of earthquakes in New Zealand
• 2004 Tasman Sea earthquake
• 2016 Te Araroa earthquake
• 2016 Kaikōura earthquake

{{wikinews|Three earthquakes hit off New Zealand's coastal areas, residents warned to avoid coast}}

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{{reflist}}

• [https://www.youtube.com/watch?v=Y1sG3rb5d9o M8.1 Earthquake and Minor Tsunami Hits New Zealand – Mar. 5, 2021]
• {{EQ-isc-link|619918421}}
• {{EQ-isc-link|620360228}}

{{Earthquakes in 2021}}

{{Earthquakes in New Zealand}}

Category:Earthquakes in New Zealand

Kermadec Islands

Kermadec Islands earthquake

Category:Kermadec Islands

Kermadec Islands earthquake

Category:Megathrust earthquakes in Oceania

Kermadec

Kermadec