2009 Fiordland earthquake

Coordinates: 45°45′43″S 166°33′43″E / 45.762°S 166.562°E / -45.762; 166.562
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2009 Fiordland earthquake
2009 Fiordland earthquake is located in New Zealand
2009 Fiordland earthquake
UTC time2009-07-15 09:22:29
ISC event15157724
USGS-ANSSComCat
Local date15 July 2009
Local time9:22 pm (NZST)
Magnitude7.8 Mw
Depth12.0 km (7.5 mi)
Epicentre45°45′43″S 166°33′43″E / 45.762°S 166.562°E / -45.762; 166.562
Areas affectedNew Zealand
Max. intensityMMI VI (Strong)[1]
Tsunami2.3 m (7 ft 7 in)
Aftershocks>100
Casualties0

The 2009 Fiordland earthquake struck the South Island of New Zealand with a magnitude of 7.8[1] at 9:22 pm (NZST) on 15 July. The earthquake was centred in the remote region of Fiordland, with the epicentre located 150 km (93 mi) west-north-west of Invercargill near Dusky Sound in Fiordland National Park, at a depth of 12 km (7.5 mi).[1][2] It is among the largest New Zealand earthquakes to occur, including the Kaikōura earthquake in 2016 and the 1931 Hawke's Bay earthquake, which both had a magnitude of 7.8.[3][4]

Earthquake[edit]

The earthquake's epicentre was located near Resolution Island in Dusky Sound, Fiordland.[5][6] It was a reverse fault, with the Indo-Australian Plate subducting beneath the Pacific Plate.[3] A large area of land around the epicentre was lifted by approximately 1 metre.[7]

New Zealand's Institute of Geological and Nuclear Sciences (GNS Science) initially measured the earthquake at magnitude 6.6,[8] but later revised the magnitude to 7.8.[9] The country's last earthquake with this magnitude was about 80 years prior in the 1931 Hawke's Bay earthquake.[3][10]

The earthquake ruptured southwards and towards the surface, and most of the earthquake's energy was offshore. This, and GNS Science describing the earthquake as being relatively slow and having a low frequency of shaking, is what caused the earthquake to do little damage compared to what people may typically expect from earthquakes of this magnitude. Another factor was the earthquake's remote location.[5]

The reported energy release was compared to "500 million tonnes of TNT, [and] 25,000 times more powerful than the atomic bomb dropped on Nagasaki in 1945".[11]

GNS Science recorded thousands of aftershocks, most of which went unnoticed.[12] One of the larger aftershocks was magnitude 6.1, which occurred 19 minutes after the main earthquake.[13]

Response[edit]

From 9.30 pm, KiwiRail trains south of Omaru and in Buller Gorge stopped, but were operational again by midnight due to a lack of damage. There were a few train delays following this.[13]

Prime Minister John Key said that people could "thank their lucky stars" due to the lack of damage caused by the earthquake.[6]

Effects[edit]

NASA map showing epicentre of earthquake and its aftershocks

The earthquake was felt throughout the South Island, and in the lower North Island as far as New Plymouth. No injuries or fatalities were reported, and it caused only minor damage.[9] Power outages were experienced in several parts of the South Island.[14][15] Over 1,500 claims for damage had been listed with the Earthquake Commission, New Zealand's agency for earthquake compensation.[16]

Landslides in the Fiordland National Park near Dusky Sound cleared large tracts of forest.[11] The earthquake brought the township of Te Anau 10 centimetres closer to Australia, and Puysegur Point (at the southwestern edge of the South Island) moved about 30 centimetres closer to Australia.[17]

The quake twisted New Zealand's South Island, with Puysegur Point, on the Southwestern tip of the island, moving 30 cm closer to Australia (westward); Te Anau moved 10 cm, Bluff 3 cm and Dunedin 1 cm. It is also believed to have caused an increased stress in the southern, offshore part of the Alpine Fault.[18]

Tsunami[edit]

Tsunami warnings were issued soon after the earthquake by authorities in New Zealand and Australia, as well as the Pacific Tsunami Warning Center in Hawaii.[19] Civil defence officials in Southland also issued a 'potential tsunami' warning, stating their concerns about widely varying measurements of the earthquake.[14] Reacting to the Pacific warnings, about fifty residents and tourists on Lord Howe Island were evacuated, and in Sydney a theatre in Bondi Beach was evacuated, and residents told to keep away from the shore.[20] the tsunami reached a height of 1 metre in Jackson Bay, 25 cm at Charleston, 12 cm at Dog Island, 14 cm at Port Kembla, and 6 cm at Spring Bay.[21] A maximum run-up of 230 cm was recorded, however, the tsunami may have been higher in some areas that were not surveyed due to the remoteness of the affected area.[22] The tsunami warnings were subsequently cancelled or reduced.[9]

See also[edit]

References[edit]

  1. ^ a b c "Magnitude 7.8 – OFF WEST COAST OF THE SOUTH ISLAND, N.Z." USGS. 15 July 2009. Archived from the original on 12 August 2009. Retrieved 15 July 2009.
  2. ^ "New Zealand Earthquake Report – Jul 15 2009 at 9:22 pm (NZST)". GeoNet. 15 July 2009. Archived from the original on 18 July 2009. Retrieved 16 July 2009.
  3. ^ a b c "Fiordland quake biggest for 80 years". GeoNet. Institute of Geological and Nuclear Sciences. 16 July 2009. Archived from the original on 18 July 2009. Retrieved 21 July 2009.
  4. ^ NZPA (19 July 2009). "Weaker, more frequent Fiordland aftershocks". Stuff.co.nz. Archived from the original on 22 July 2009. Retrieved 21 July 2009.
  5. ^ a b "GeoNet M7.8 Dusky Sound Wed, Jul 15 2009". www.geonet.org.nz. Retrieved 20 May 2024.
  6. ^ a b Gorman, Paul (17 August 2009). "'Soft rocks' prevented earthquake damage". Stuff. Retrieved 21 May 2024.
  7. ^ "Ground raised one metre by quake". Radio New Zealand. 18 July 2009. Archived from the original on 27 July 2009. Retrieved 21 July 2009.
  8. ^ "Tsunami alert after NZ earthquake". BBC News. 15 July 2009. Retrieved 15 July 2009.
  9. ^ a b c NZPA, Fairfax (15 July 2009). "Fiordland quake measures 7.8". stuff.co.nz. Retrieved 15 July 2009.
  10. ^ "Nine years ago: NZ's forgotten magnitude 7.8 monster quake struck Fiordland". The New Zealand Herald. 18 July 2018. Retrieved 20 May 2024.
  11. ^ a b Yvonne Tahana (17 July 2009). "After-shocks continue in Southland". New Zealand Herald. Archived from the original on 21 October 2012. Retrieved 21 July 2009.
  12. ^ "Aftershocks from large quake continue in Fiordland". RNZ. 28 July 2009. Retrieved 21 May 2024.
  13. ^ a b "Aftershocks hit Fiordland after quake". Otago Daily Times. 17 July 2009. Retrieved 21 May 2024.
  14. ^ a b Dye, Stuart; NZPA (15 July 2009). "South Island quake prompts 'potential tsunami' warning". The New Zealand Herald. Retrieved 15 July 2009.
  15. ^ "Quake strikes off New Zealand's Southland". Xinhua. 15 July 2009. Archived from the original on 17 July 2009. Retrieved 15 July 2009.
  16. ^ Cowlishaw, Shane (31 July 2009). "Quake claims rise to almost $3 million". Southland Times. Retrieved 20 May 2024 – via Stuff.
  17. ^ Ramnarayan, Abhinav (22 July 2009). "Earthquake brings New Zealand closer to Australia". The Guardian. ISSN 0261-3077. Retrieved 20 May 2024.
  18. ^ Paul Gormon (22 July 2009). "Our Australian cousins just got closer". The Press. Fairfax Media. Archived from the original on 26 July 2009. Retrieved 21 July 2009.
  19. ^ Beckford, Gyles (15 July 2009). "New Zealand quake sparks tsunami warnings". Reuters. Retrieved 15 July 2009.
  20. ^ "Fiordland quake causes evacuation in Sydney". Television New Zealand News. 16 July 2009. Archived from the original on 18 July 2009. Retrieved 21 July 2009.
  21. ^ "M 7.8 - 97 km WSW of Te Anau, New Zealand". earthquake.usgs.gov. Retrieved 28 October 2021.
  22. ^ Uslu, B.; Power, W.; Greenslade, D.; Eblé, M.; Titov, V. (2011). "The July 15, 2009 Fiordland, New Zealand Tsunami: Real-Time Assessment". Pure and Applied Geophysics. 168 (11): 1963–1972. Bibcode:2011PApGe.168.1963U. doi:10.1007/s00024-011-0281-7. S2CID 140714530.

Further reading[edit]

  • Rogers, Anna (2013) [1996]. The Shaky Isles: New Zealand Earthquakes (2 ed.). Wellington: Grantham House. pp. 185, 186. ISBN 978-1-86934-119-0.
  • Wright, Matthew (2014). Living on shaky ground: The science and story behind New Zealand's earthquakes. Auckland: Random House (New Zealand). pp. 174, 175. ISBN 978-1-77553-688-8.

External links[edit]

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