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 Dusky Sound 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
TypeReverse fault
Areas affectedNew Zealand
Max. intensityMMI VI (Strong)[1]
Tsunami2.3 m (7 ft 7 in)
Aftershocks>1,000
Casualties0

On 15 July 2009 at 9:22 pm (NZST), a magnitude 7.8 earthquake struck a remote region of Fiordland, in the South Island of New Zealand. Its epicentre was 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 1931 Hawke's Bay earthquake and the 2016 Kaikōura earthquake, which both had a magnitude of 7.8.[3][4]

Background[edit]

New Zealand experiences approximately 20,000 earthquakes per year, with about 250 being strong enough to be felt.[5] The Dusky Sound earthquake followed considerable seismic activity in northern Fiordland since 1988; six earthquakes above magnitude 6.0 struck the region before 2009,[6][7] including one measuring 7.2 Ms  in 2003.[7]

The last time the country experienced an earthquake with a magnitude this high was from the 1931 Hawke's Bay earthquake.[3][8] It took until the 2016 Kaikōura earthquake for New Zealand to experience another earthquake measuring Mw 7.8.[9]

Earthquake[edit]

The magnitude 7.8 earthquake started at 9:22 pm,[10] with an epicentre near Resolution Island in Dusky Sound, Fiordland,[11][12] which is 160 km north-west of Invercargill.[2] Shaking reportedly lasted for at least a minute,[13] and was felt throughout the South Island, and in the lower North Island as far as New Plymouth.[14] It was a reverse fault earthquake, with the Indo-Australian Plate subducting beneath the Pacific Plate.[3]

New Zealand's Institute of Geological and Nuclear Sciences (GNS Science) initially measured the earthquake at magnitude 6.6,[13] but later revised the magnitude to 7.8.[14] It was in the world's top five biggest earthquakes of 2009.[15]

The earthquake started at a depth of 30 kilometres (19 mi) and ruptured southwards and towards the surface,[11] with focal depth of 12 km (7.5 mi).[2] Most of the earthquake's energy was focussed out in the Tasman Sea.[11][9] GNS Science described the earthquake as relatively slow with low frequency of shaking.[11][16]

Thousands of aftershocks occurred, with most being too small to be felt.[17] One of the larger aftershocks was magnitude 6.1, which occurred 19 minutes after the main earthquake.[18]

Response[edit]

From 9:30 pm, KiwiRail trains south of Oamaru and in Buller Gorge were stopped to check for damage. Because no damage was found, they were operational again by midnight. This caused a few delays.[18]

Prime Minister John Key said that people could "thank their lucky stars" due to the lack of damage caused by the earthquake.[12]

Effects[edit]

NASA map showing epicentre of earthquake and its aftershocks

No injuries or fatalities were reported, and it caused only minor damage,[14] which people may find unexpected for an earthquake of this magnitude. The low damage was caused by the earthquake's remote location, slow speed and its relatively low shaking frequency.[11][16] Power outages were experienced in several parts of the South Island.[19][20] By 2010 about 5,219 claims for damage had been listed with the Earthquake Commission, New Zealand's agency for earthquake compensation, totalling $6.1 million.[15]

Landslides in the Fiordland National Park near Dusky Sound cleared large tracts of forest.[21] The quake twisted the South Island, with Puysegur Point, on the Southwestern tip of the island, moving 30 cm closer to Australia (westward); Te Anau moved 10 cm closer, Bluff 3 cm and Dunedin 1 cm.[22][23] It is also believed to have caused an increased stress in the southern, offshore part of the Alpine Fault.[23][6]

A large area of land around the epicentre was lifted by approximately 1 metre.[24]

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.[25] Civil defence officials in Southland also issued a 'potential tsunami' warning, stating their concerns about widely varying measurements of the earthquake.[19] 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.[26] 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.[27] 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.[28] The tsunami warnings were subsequently cancelled or reduced.[14]

See also[edit]

References[edit]

  1. ^ a b "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. ^ a b c "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. ^ "GeoNet Earthquake FAQ". www.geonet.org.nz. Retrieved 31 May 2024.
  6. ^ a b Mahesh, P.; Kundu, Bhaskar; Catherine, J. K.; Gahalaut, V. K. (1 January 2011). "Anatomy of the 2009 Fiordland earthquake (Mw 7.8), South Island, New Zealand". Geoscience Frontiers. 2 (1): 17–22. doi:10.1016/j.gsf.2010.12.002. ISSN 1674-9871.
  7. ^ a b "M 7.8 - 97 km WSW of Te Anau, New Zealand". earthquake.usgs.gov. Retrieved 31 May 2024.
  8. ^ "Nine years ago: NZ's forgotten magnitude 7.8 monster quake struck Fiordland". The New Zealand Herald. 18 July 2018. Retrieved 20 May 2024.
  9. ^ a b "M7.8 Kaikoura quake the biggest since the Dusky Sound jolt in 2009". GNS Science | Te Pῡ Ao. Retrieved 1 June 2024.
  10. ^ "A magnitude 7.8 earthquake occurred 90 km north-west of Tuatapere, New Zealand on Wed Jul 15 2009 9:22 PM. The quake was 12 kilometres deep and the shaking was severe close to the quake". www.geonet.org.nz. Retrieved 25 May 2024.
  11. ^ a b c d e "GeoNet M7.8 Dusky Sound Wed, Jul 15 2009". www.geonet.org.nz. Retrieved 20 May 2024.
  12. ^ a b Gorman, Paul (17 August 2009). "'Soft rocks' prevented earthquake damage". Stuff. Retrieved 21 May 2024.
  13. ^ a b "Tsunami alert after NZ earthquake". BBC News. 15 July 2009. Retrieved 15 July 2009.
  14. ^ a b c d NZPA, Fairfax (15 July 2009). "Fiordland quake measures 7.8". stuff.co.nz. Retrieved 15 July 2009.
  15. ^ a b "Earthquake Commission 2009–2010 Annual Report" (PDF). Earthquake Commission. 2010. Retrieved 24 May 2024.
  16. ^ a b Cowlishaw, Shane (31 July 2009). "Quake claims rise to almost $3 million". Southland Times. Retrieved 20 May 2024 – via Stuff.
  17. ^ "Aftershocks from large quake continue in Fiordland". RNZ. 28 July 2009. Retrieved 21 May 2024.
  18. ^ a b "Aftershocks hit Fiordland after quake". Otago Daily Times. 17 July 2009. Retrieved 21 May 2024.
  19. ^ a b Dye, Stuart; NZPA (15 July 2009). "South Island quake prompts 'potential tsunami' warning". The New Zealand Herald. Retrieved 15 July 2009.
  20. ^ "Quake strikes off New Zealand's Southland". Xinhua. 15 July 2009. Archived from the original on 17 July 2009. Retrieved 15 July 2009.
  21. ^ 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.
  22. ^ Ramnarayan, Abhinav (22 July 2009). "Earthquake brings New Zealand closer to Australia". The Guardian. ISSN 0261-3077. Retrieved 20 May 2024.
  23. ^ a b 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.
  24. ^ "Ground raised one metre by quake". Radio New Zealand. 18 July 2009. Archived from the original on 27 July 2009. Retrieved 21 July 2009.
  25. ^ Beckford, Gyles (15 July 2009). "New Zealand quake sparks tsunami warnings". Reuters. Retrieved 15 July 2009.
  26. ^ "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.
  27. ^ "M 7.8 - 97 km WSW of Te Anau, New Zealand". earthquake.usgs.gov. Retrieved 28 October 2021.
  28. ^ 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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