2021 Kermadec Islands earthquakes

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2021 Kermadec Islands earthquakes
2021 Kermadec Islands earthquakes is located in Oceania
2021 Kermadec Islands earthquakes
UTC time2021-03-04 17:41:25
 2021-03-04 19:28:31
ISC event619918377
 619916487
USGS-ANSSComCat
 ComCat
Local dateMarch 5, 2021 (2021-03-05)
Local time06:41:25 NZDT
 08:28:31 NZDT
Magnitude7.4 Mw
 8.1 Mw
Depth43.0 km (27 mi)
 28.9 km (18 mi)
Epicenter29°44′06″S 177°16′55″W / 29.735°S 177.282°W / -29.735; -177.282Coordinates: 29°44′06″S 177°16′55″W / 29.735°S 177.282°W / -29.735; -177.282
FaultKermadec-Tonga subduction zone
TypeMegathrust
Areas affectedNew Zealand; Pacific islands
Total damageLimited
Max. intensityVIII (Severe)
TsunamiUp to 0.64 m (2.1 ft) in Norfolk Island
Aftershocks1,115 (as of 13 September 2021)[1]
strongest being 6.5 Mw
Casualtiesnone

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 epicentre was located south of Raoul Island in the Kermadec Islands, part of the New Zealand outlying islands.[2] The earthquake was preceded by a magnitude 7.4 foreshock[3] and followed by a magnitude 6.1 aftershock.[4] A separate, unrelated magnitude 7.3 earthquake occurred off the coast of the North Island of New Zealand, approximately 900 km to the south, several hours before the main quakes.[5] As of September 2 2021, there have been thousands of aftershocks, with more than a dozen of them exceeding magnitude 6.[6]

Tectonic setting[]

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.[7]

Earthquakes[]

The main 8.1 magnitude 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 175 by 75 km (109 by 47 mi) in area.[2] 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).[3]

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 100 km (60 mi) off the east coast of the North Island[8] and was felt largely across the country.[9][5] This earthquake was considered an independent event.[2][10] A flooding warning was issued due to this quake, which was rescinded before the other quakes hit.[11]

There were no reports of serious damage or injuries caused by the earthquakes.[12] The volcano webcam on the island ceased to function from 08:24 NZDT on 5 March 2021.[relevant?]

Other events[]

On July 29, 2021, nearly 5 months after the Kermadecs mainshock, an 8.2 magnitude earthquake struck the Alaska Peninsula,[13] and another 8.1 magnitude earthquake struck the Sub-Antarctic British territory of the South Sandwich Islands on August 12 of that year.[14] This is unusual since earthquakes of magnitude 8 or higher occur only about once every year on average.[15] 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.[16]

Aftershocks[]

As of September 2 2021, there have been at least 1,096 aftershocks above 4.0 magnitude.[1] and 13 of them above magnitude 6.[6] On 20 June 2021, a magnitude 6.5 earthquake struck at a depth of 25 km.[17] It is currently the largest earthquake of the aftershock sequence.

Tsunami[]

The main quake lead to tsunami warnings being issued around the Pacific, as far away as Peru, but particularly for the North Island of New Zealand.[18] Thousands of Kiwis evacuated to higher ground.[19] 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.[20] The tsunami land threat was dropped at 1:27 pm NZDT to a "Beach and Marine threat."[21] While the tsunami heights were initially predicted to be 1-3 metres high,[22] tsunami heights measured by GeoNet ended up being around 0.35–0.40 m (1.1–1.3 ft) at East Cape and around 0.15–0.20 m (0.49–0.66 ft) at Great Barrier Island;[23] 0.64 m (2.1 ft) waves were reported in Norfolk Island.[19] The tsunami heights at Raoul Island from the main quake were not able to be measured because the earthquake destroyed the island's monitoring equipment.[24]

See also[]

References[]

  1. ^ Jump up to: a b "USGS earthquake catalog". United States Geological Survey.
  2. ^ Jump up to: a b c "M 8.1 - Kermadec Islands region". USGS-ANSS. Retrieved 4 March 2021.
  3. ^ Jump up to: a b "M 7.4 - Kermadec Islands, New Zealand". USGS-ANSS. Retrieved 4 March 2021.
  4. ^ "M 6.1 - Kermadec Islands region". USGS-ANSS. Retrieved 4 March 2021.
  5. ^ Jump up to: a b "GeoNet News: A morning of large offshore earthquakes - what happened and future scenarios". www.geonet.org.nz. Retrieved 5 March 2021.
  6. ^ Jump up to: a b "USGS earthquake Catalog". United States Geological Survey.
  7. ^ M. J. Funnell, C. Peirce, W. R. Stratford, M. Paulatto, A. B. Watts, I. Grevemeyer (2014). "Structure and deformation of the Kermadec forearc in response to subduction of the Pacific oceanic plate". Geophysical Journal International. 199 (2): 1286–1302. doi:10.1093/gji/ggu330. Retrieved 5 March 2021.CS1 maint: multiple names: authors list (link)
  8. ^ "M 7.3 - 174 km NE of Gisborne, New Zealand". USGS. 4 March 2021. Retrieved 5 March 2021.
  9. ^ "Magnitude 7.3, Fri Mar 5 2021 2:27 AM". GeoNet. 5 March 2021. Retrieved 23 May 2021.
  10. ^ "Earthquake near New Zealand with Pacific tsunami threat". Washington Post. 5 March 2021. Retrieved 5 March 2021. A magnitude 7.3 hit near New Zealand early on Thursday, [...] occurred far enough apart that they likely were not related.
  11. ^ "Earthquake cluster and tsunami alert: what you need to know". Stuff. 5 March 2021. Retrieved 7 March 2021.
  12. ^ "Thousands of New Zealanders allowed to return home after tsunami alert". The Guardian. 5 March 2021. Retrieved 5 March 2021.
  13. ^ "M 8.2 - 91 km ESE of Perryville, Alaska". United States Geological Survey. 29 July 2021. Retrieved 23 August 2021.
  14. ^ "M 8.1 - South Sandwich Islands region". United States Geological Survey. Retrieved 23 August 2021.
  15. ^ "How Often Do Earthquakes Occur?". Incorporated Research Institutions for Seismology. Retrieved 23 August 2021.
  16. ^ "Significant Earthquakes - 2007". earthquake.usgs.gov. USGS. Retrieved 23 August 2021.
  17. ^ "M 6.5 - Kermadec Islands, New Zealand". United States Geological Survey. 20 June 2021.
  18. ^ "Live: 'Try and stay calm' says emergency management minister, tsunami waves expected for 'several hours' after earthquake". Stuff. 4 March 2021. Retrieved 4 March 2021.
  19. ^ Jump up to: a b Pearson, Nick (5 March 2021). "Tsunami threat passes in New Zealand, as evacuees allowed to return". 9 News. Retrieved 5 March 2021.
  20. ^ "Major 8.1 quake at Kermadecs, people told to move to higher ground". Radio New Zealand. 5 March 2021. Retrieved 5 March 2021.
  21. ^ "National Emergency Management Agency on Twitter". Twitter.
  22. ^ "Earthquake swarm: North Island tsunami warning lifted after 8.1 shake, evacuees return home". NZ Herald. 5 March 2021. Retrieved 23 August 2021.
  23. ^ "GeoNet News". www.geonet.org.nz. Retrieved 5 March 2021.
  24. ^ "Raoul Island tsunami monitoring equipment knocked out during Friday's earthquakes restored by GNS team". Stuff. 11 March 2021. Retrieved 24 April 2021.

External links[]

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