The 2021 Kermadec Islands earthquakes were a series of earthquakes with magnitudes of 8.1 and 7.4 that occurred at 19:28:31 UTC on 4 March 2021. The epicentres were located southeast of

Raoul Island Raoul Island (''Sunday Island'') is the largest and northernmost of the main Kermadec Islands, south south-west of 'Ata Island of Tonga and north north-east of New Zealand's North Island. It has been the source of vigorous volcanic activity ...

in the

Kermadec Islands The Kermadec Islands ( mi, Rangitāhua) are a subtropical island arc in the South Pacific Ocean northeast of New Zealand's North Island, and a similar distance southwest of Tonga. The islands are part of New Zealand. They are in total are ...

, part of the

New Zealand outlying islands The New Zealand outlying islands are nine offshore island groups that are part of New Zealand, with all but Solander Islands lying beyond the 12nm limit of the mainland's territorial waters. Although considered an integral parts of New Zealand, ...

. The main magnitude 8.1 earthquake was preceded by a magnitude 7.4

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

and followed by a magnitude 6.1

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

. A separate, unrelated magnitude 7.3 earthquake occurred off the coast of the

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...

of New Zealand, approximately 900 km to the south, several hours before the main quakes. As of January 2023, there have been nearly 3,000 aftershocks, with more than a dozen of them exceeding magnitude 6.

Tectonic setting

The

Kermadec-Tonga subduction zone The Kermadec-Tonga subduction zone is a convergent plate boundary that stretches from the North Island of New Zealand northward. The formation of the Kermadec and Tonga Plates started about 4–5 million years ago. Today, the eastern boundary ...

runs east of the Kermadec Islands and marks the boundary between the

Australian Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal Au ...

and Pacific plates. This convergent boundary is where the denser Pacific Plate

subducts Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

or dives beneath the less dense Australian Plate.

Earthquakes

The main magnitude 8.1

megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthqua ...

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 The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...

estimated that the rupture zone was 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). There were no reports of serious damage or injuries caused by the earthquakes. Th
volcano webcam
on the island ceased to function from 08:24 NZDT on 5 March 2021.

Other events

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 off

East Cape East Cape is the easternmost point of the main islands of New Zealand. It is located at the northern end of the Gisborne District of New Zealand's North Island. It can also refer to the broader Gisborne cape. East Cape was originally named "C ...

in the

. This earthquake was felt largely across the country, and woke many people up, but no damage was caused. This earthquake was considered an independent event. A flooding warning was issued due to this quake, which was rescinded before the other quakes hit. On July 29, 2021, nearly 5 months after the Kermadec Islands mainshock, an 8.2 magnitude earthquake struck the

Alaska Peninsula The Alaska Peninsula (also called Aleut Peninsula or Aleutian Peninsula, ale, Alasxix̂; Sugpiaq: ''Aluuwiq'', ''Al'uwiq'') is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. The ...

, and another 8.1 magnitude earthquake struck the Sub-Antarctic British territory of the

South Sandwich Islands ) , anthem = "God Save the King" , song_type = , song = , image_map = South Georgia and the South Sandwich Islands in United Kingdom.svg , map_caption = Location of South Georgia and the South Sandwich Islands in the southern Atlantic Oce ...

on August 12 of that year. This is unusual since earthquakes of magnitude 8 or higher occur only about once every year on average. There is no evidence of a causal relationship between the three events.

2021 File:2021 collage V2.png, From top left, clockwise: the James Webb Space Telescope was launched in 2021; Protesters in Yangon, Myanmar following the 2021 Myanmar coup d'état, coup d'état; A civil demonstration against the October–November 2021 ...

has had the most 8.0+ earthquakes in a single year since 2007.

Aftershocks

As of January 2 2023, there have been at least 2,792 aftershocks above 4.0 magnitude. and 13 of them above magnitude 6. On March 2 2022, nearly a year after the mainshock, a magnitude 6.6 earthquake struck at a depth of 37 km, very close to

. It is currently the largest earthquake of the aftershock sequence.

Impact

According to

GeoNet GeoNet was an early international on-line services network built using microcomputers. Based on software developed in Germany by GeoNet Systems GmbH in the early 1980s, and completed in the early 1990s, it was one of the first networks to offer a ...

, the mainshock caused more than 300 landslides on steep forest cliffs and rugged coastal cliffs on

. The largest slide was at Pills Beach, where about 400 meters of coastal cliffs collapsed, leaving a column of sediment in the ocean. A few buildings were damaged in

. However there were no casualties as the island was uninhabited at the time due to the

COVID-19 pandemic The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...

Tsunami

The main quake led to

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

warnings being issued around the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, as far away as

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, but particularly for the

of New Zealand. Thousands of Kiwis evacuated to higher ground.

NEMA The National Electrical Manufacturers Association (NEMA) is the largest trade association of electrical equipment manufacturers in the United States. Founded in 1926, it advocates for the industry, and publishes standards for electrical product ...

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 The Bay of Plenty ( mi, Te Moana-a-Toi) is a region of New Zealand, situated around a bight of the same name in the northern coast of the North Island. The bight stretches 260 km from the Coromandel Peninsula in the west to Cape Runawa ...

, Gisborne, and

Great Barrier Island Great Barrier Island ( mi, Aotea) lies in the outer Hauraki Gulf, New Zealand, north-east of central Auckland. With an area of it is the sixth-largest island of New Zealand and fourth-largest in the main chain. Its highest point, Mount Hobson ...

. The tsunami land threat was dropped at 1:27 pm NZDT to a "Beach and Marine threat." While the tsunami heights were initially predicted to be high, tsunami heights measured by GeoNet ended up being around at

and around at Great Barrier Island; waves were reported in

Norfolk Island Norfolk Island (, ; Norfuk: ''Norf'k Ailen'') is an external territory of Australia located in the Pacific Ocean between New Zealand and New Caledonia, directly east of Australia's Evans Head and about from Lord Howe Island. Together with ...

. The tsunami heights at

from the main earthquake are estimated to have reached , 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. In

Port-Vila Port Vila (french: Port-Vila), or simply Vila (; french: Vila; bi, Vila ), is the Capital city, capital and largest city of Vanuatu. It is located on the Efate, island of Efate. Its population in the last census (2009) was 44,040, an incre ...

Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (french: link=no, République de Vanuatu; bi, Ripablik blong Vanuatu), is an island country located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of no ...

, a few boats were damaged and several people were injured.

References

External links

M8.1 Earthquake and Minor Tsunami Hits New Zealand - Mar. 5, 2021
* * {{Earthquakes in New Zealand Earthquakes in New Zealand

Kermadec Islands earthquake Kermadec Islands Kermadec Islands earthquake Megathrust earthquakes

Kermadec Kermadec or de Kermadec may refer to: Geography * Kermadec Islands, a subtropical island arc in the South Pacific Ocean northeast of New Zealand * Kermadec Plate, a long narrow tectonic plate located west of the Kermadec Trench * Kermadec Trench, ...

2021 disasters in New Zealand