1974 Dunedin earthquake
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| UTC time | 1974-04-09 07:49:46 |
|---|---|
| Local date | 9 April 1974 |
| Local time | 7:49 pm |
| Magnitude | 4.9 M or 5.0 M |
| Epicentre | 45°58′S 170°31′E / 45.97°S 170.52°E[1] |
The 1974 Dunedin earthquake was a magnitude 4.9 or 5.0 earthquake that occurred near the New Zealand city of Dunedin on 9 April 1974. With Dunedin being an area of New Zealand that rarely experiences earthquakes, this was the largest earthquake to have occurred in the city since its founding in the 1840s, and the first to cause damage. Over 3,000 damage claims were lodged with the Earthquake and War Damage Commission, which paid out about $250,000 (equivalent to $3,600,000 in 2026). This is considered unusually high for an earthquake with a magnitude this low. Most damage was to houses and involved chimneys.
Tectonic setting
[edit]Eastern Otago is considered a "tectonically stable" area for New Zealand, meaning significant earthquakes rarely occur in the area. Most earthquakes that are felt in eastern Otago originate from Fiordland, which is "highly active", and is about 200–300 kilometres to the west.[2] In the 70 years leading up to 1974, Dunedin experienced at least four earthquakes measuring at least V (moderate) on the Modified Mercalli intensity scale.[3]
Earthquake
[edit]The earthquake struck Dunedin at approximately 7:49 pm on 9 April 1974.[4] Its epicentre was located offshore, about 5 kilometres south of the suburb of St Clair,[4] and had a depth of 12 or 20 kilometres.[5][6][1] It either had a magnitude of 4.9 or 5.0[7][5][1] and a maximum intensity of VIII (Severe) or VII (Very strong) on the Modified Mercalli intensity scale.[8][7] A peak ground acceleration of 0.27g (0.27 times the acceleration of Earth's gravity) was measured in St Clair.[7][3] The earthquake was described as being "sharp" and having a "strong vertical motion".[3] Seismologists are uncertain on which fault the earthquake was located, but it is believed to have been on the Green Island Fault, as it is the closest to the epicentre.[5][7] There were aftershocks at 8:20 pm and 9:50 pm, which both had a magnitude of 3.7.[4][7]
The earthquake caused power outages, chimneys to fall down[4] and the telephone system to be overloaded. It was reported to have broken windows and caused cracks to appear in "a number" of buildings.[5] It took about 45 minutes for power to be restored to Corstorphine.[5] False alarms from automatic warning systems caused all of Dunedin's available fire appliances to be dispatched.[7]
The Earthquake and War Damage Commission received about 3,000 damage claims,[4] and paid out about $250,000 (equivalent to $3,600,000 in 2026) which is "extraordinarily large" for an earthquake of this magnitude,[3] and was the highest since the 1968 Inangahua earthquake.[6] The claims mostly related to houses, with over half of them involving damaged chimneys.[3] Chimney damage was "consistent and widespread" in the "southern suburbs of the alluvium between Otago Peninsula and St Clair" according to Adams and Keans, and occurred throughout the rest of the city but in lower numbers.[9] Many claims involved masonry damage,[8][9] plumbing damage and interior plaster being cracked.[7][9] Damage was mostly minor.[5] Bricks fell out of Knox Church.[7]
This was the first earthquake in Dunedin to cause widespread damage since its founding in the 1840s, and as of 1990 was the strongest earthquake to have hit the city.[2][3][7] As of 2015, the largest earthquake to have occurred in the area since 1974 was a magnitude 4.7 earthquake in 2015.[10] A commemorative event was held on the 50th anniversary of the earthquake, in 2024. It included a short film about the earthquake, made by a University of Otago student.[8]
References
[edit]- ^ a b c "Magnitude 4.9, Tue Apr 9 1974 7:49 PM". GeoNet. Retrieved 14 June 2024.
- ^ a b Adams, R. D.; Kean, R. J. (30 September 1974). "The Dunedin earthquake, 9 April 1974: Part 1: seismological studies". Bulletin of the New Zealand Society for Earthquake Engineering. 7 (3): 115–122. doi:10.5459/bnzsee.7.3.115-122. ISSN 2324-1543.
- ^ a b c d e f Bishop, D. G. (30 September 1974). "The Dunedin earthquake, 9 April, 1974: Part 2: local effects". Bulletin of the New Zealand Society for Earthquake Engineering. 7 (3): 123–129. doi:10.5459/bnzsee.7.3.123-129. ISSN 2324-1543.
- ^ a b c d e Gorman, Paul (14 July 2016). "Could Dunedin be hit by a large, local earthquake?". Stuff. Retrieved 14 June 2024.
- ^ a b c d e f "The last good shake". Otago Daily Times. 18 September 2010. Retrieved 14 June 2024.
- ^ a b "The Dunedin Earthquake, 9 April 1974 Part 1". New Zealand Society for Earthquake Engineering. Retrieved 14 June 2024.
- ^ a b c d e f g h i Gorman, Paul (26 September 2020). "The day the earth moved". The Otago Daily Times. Retrieved 14 June 2024.
- ^ a b c Littlewood, Matthew (8 April 2024). "Information event to commemorate earthquake". Otago Daily Times. Retrieved 14 June 2024.
- ^ a b c "Seismic Risk in the Otago Region" (PDF). Otago Regional Council. March 2005. pp. 21–22. Retrieved 14 June 2024.
- ^ "Dunedin quake biggest for 40 years – GNS". RNZ. 2 June 2015. Retrieved 23 May 2026.
External links
[edit]- Map of damage in shops by GNS Science