M7.6 Earthquake Off Tonga - 2023-05-10

[davenn]

M 7.6 - 95 km WNW of Hihifo, Tonga​

• 2023-05-10 16:02:00 (UTC)
• 15.600°S 174.608°W
• 210.1 km depth

A decent event that maxed out my seismo for some minutes
https://www.sydneystormcity.com/seismograms.htm

As it will disappear off my seismo in around 20 hours ( from time of writing this) a screen grab below
saved for posterity

cheers
Dave

 

[Astronuc]

Fairly deep at 201 km.

https://earthquake.usgs.gov/earthquakes/eventpage/us6000kawn/executive

https://earthquake.usgs.gov/earthquakes/eventpage/us6000kawn/region-info

Seismotectonics of the Eastern Margin of the Australia Plate

The eastern margin of the Australia plate is one of the most sesimically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand.

Since 1900 there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

North of New Zealand, the Australia-Pacific boundary stretches east of Tonga and Fiji to 250 km south of Samoa. For 2,200 km the trench is approximately linear, and includes two segments where old (>120 Myr) Pacific oceanic lithosphere rapidly subducts westward (Kermadec and Tonga). At the northern end of the Tonga trench, the boundary curves sharply westward and changes along a 700 km-long segment from trench-normal subduction, to oblique subduction, to a left lateral transform-like structure.

https://earthquake.usgs.gov/earthquakes/tectonic/images/emaustralia_tsum.pdf

 

[davenn]

Fairly deep at 201 km.

https://earthquake.usgs.gov/earthquakes/eventpage/us6000kawn/executive
https://earthquake.usgs.gov/earthquakes/eventpage/us6000kawn/region-info
https://earthquake.usgs.gov/earthquakes/tectonic/images/emaustralia_tsum.pdf

Yup, getting down there
""Since 1900 there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.""

I remember the Macquarie Rdg 1989 event, that was during my first year doing geology at Otago University.
I have a photocopy of the seismogram for that event from the geology dept seismograph was still an ink on paper at that time. It was a definitly a big talking point at the time.

Interestingly it didnt mention some of the other M8+ events in that text I quoted from your post.
The last one just a couple of years ago in the Kermadecs area. It was preceeded by a M7.(3?) or was it 7.5, cant remember. Also a couple of M8+ events further north towards Fiji.

OK gotta go and dig up the info hahaha .......

 

[davenn]

M 8.1 - Kermadec Islands, New Zealand​

• 2021-03-04 19:28:33 (UTC)
• 29.723°S 177.279°W
• 28.9 km depth

M 8.2 - 267 km E of Levuka, Fiji​

• 2018-08-19 00:19:40 (UTC)
• 18.113°S 178.153°W
• 600.0 km depth

M 7.9 - 45 km S of Levuka, Fiji​

• 2018-09-06 15:49:18 (UTC)
• 18.474°S 179.350°E
• 670.8 km depth

The largest quake in NZ since European settlement was in 1883 and estimated at M8.1
It was centred east of Wellington City ( the capital) had around 12 metres of max horizontal
offset and around 7 metres of vertical offset. And was, for some years, the largest measured
horizontal offset anywhere in the world.

That list, in the previous posts, missed some other significant NZ events some onland ......

M 7.8 - 53 km NNE of Amberley, New Zealand (NE South Island)​

• 2016-11-13 11:02:56 (UTC)
• 42.737°S 173.054°E
• 15.1 km depth

M 7.8 - 97 km WSW of Te Anau, New Zealand ( on the SW coast of the South Island​

• 2009-07-15 09:22:29 (UTC) Southern end of the Alpine Fault)
• 45.762°S 166.562°E
• 12.0 km depth

M 7.6 - 82 km ENE of Gisborne, New Zealand ( a bit offshore of NE North Island)​

• 1947-05-17 07:06:41 (UTC)
• 38.445°S 178.909°E
• 25.0 km depth

M 7.7 - 46 km E of Gisborne, New Zealand ( almost the same place as the above one​

a little closer to the coast)

• 1947-03-25 20:32:20 (UTC)
• 38.676°S 178.533°E
• 15.0 km depth

so yup a few holes in their info haha

cheers
Dave

 

[davenn]

USGS map for NZ region events, M7.0 and greater, since 1929 ( they dont list any earlier ones)

 

[Astronuc]

And don't forget the Darfield and Christchurch (Canterbury) Earthquakes that did significant damage to Christchurch and surrounding areas. I have a relative who lives in the Cashmere Hills areas on the south side of Christchurch. There has was slightly damage during the first quake, then received more damage during the second, which was much closer.

Darfield Earthquake, 09/03/2010, Mw7.0
Christchurch Earthquake, 02/21/2011, Mw6.1
https://d9-wret.s3.us-west-2.amazon...-public/atoms/files/NewZealand2011_slides.pdf
https://www.usgs.gov/publications/g...71-darfield-and-m-62-christchurch-new-zealand