M 7.3 - 174 km NE of Gisborne, New Zealand

  • Thread starter Astronuc
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In summary, the M7.4 earthquake occurred off the north coast of New Zealand, and may cause a tsunami if an uplift was significant.
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  • #3
jedishrfu said:
No tsunami threat?
That raises an interesting question. Often tsunamis are caused by sea bottom landslides. Is there anything in the seismic signature that might make it possible to say that the evens was a landslide rather than a fault slip?

Or could we map the continental shelf edges where landslides are most likely and automatically correlate the seismic location with one of those places?

Perhaps these things are already built-in to the tsunami warning system. I don't know.

ping @davenn
 
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  • #4
anorlunda said:
Is there anything in the seismic signature that might make it possible to say that the evens was a landslide rather than a fault slip?
Counter question: can a landslide occur if the depth is significantly under sea level? Or is it the nature of the various faults which determine which of it can happen? Or both of it?
 
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  • #6
  • #7
I have a dumb question. How does an underwater landslide cause a Tsunami?
 
  • #9
So its the stuff that falls into the ocean. The term underwater slide then seems odd. Good to know..thanks.
 
  • #10
hutchphd said:
So its the stuff that falls into the ocean. The term underwater slide then seems odd. Good to know..thanks.
The same can happen completely under water. If an earthquake makes one side of the fault drop for, say 10 meters within seconds, then imagine what will happen to, say 1000 meters of water above it? The 2004 tsunami was such an example:
https://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami
 
  • #12
fresh_42 said:
The same can happen completely under water. If a earthquake makes one side of the fault drop for, say 10 meters within seconds, then imagine what will happen to, say 1000 meters of water above it?
I guess I am caught in a semantic trap of my own making. If the Earth upon which I stand were to subside suddenly by 10 meters I would not call it a landslide. The physics is clear for an underwater subsidence. Semantics.
 
  • #13
hutchphd said:
I guess I am caught in a semantic trap of my own making. If the Earth upon which I stand were to subside suddenly by 10 meters I would not call it a landslide. The physics is clear for an underwater subsidence. Semantics.
The choice of words is personal. But this video from Geoscience Australia depicts what we're talking about.

 
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  • #14
hutchphd said:
I have a dumb question. How does an underwater landslide cause a Tsunami?
A landslide is a mass of Earth moving under gravity, and the displacement of Earth (acting under the body force, mg) imparts momentum to the water it displaces. The momentum is transmitted through water and when it comes to a boundary (e.g., land along the coast) the pressure wave is carried onto the land.
 
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  • #15
The 7.3 has now been followed by a deep 8.1 which is unusual and has a tsunami warning.
 
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  • #16
Baluncore said:
The 7.3 has now been followed by a deep 8.1 which is unusual and has a tsunami warning.
M 8.1 - Kermadec Islands, New Zealand
https://earthquake.usgs.gov/earthquakes/eventpage/us7000dflf/executive
  • 2021-03-04 19:28:31 (UTC)
  • 29.740°S 177.267°W
  • 19.4 km depth - somewhat shallow and could cause a tsunami if an uplift was significant.
M 7.4 - Kermadec Islands, New Zealand
https://earthquake.usgs.gov/earthquakes/eventpage/us7000dfk3/executive
  • 2021-03-04 17:41:25 (UTC)
  • 29.613°S 177.843°W
  • 55.6 km depth
The 8.1 Mag was preceded by a 7.4 and a bunch of smaller quakes. Blue disk is the 8.1, the red dots are recent quakes within the past hour. The 7.4 is the large orange disk to the west (left). These quakes are much further north than the 7.3 in the initial post.

The 7.3 earlier is 288.9 km (179.5 mi) E of Tauranga, Bay of Plenty, New Zealand (north coast of N Island). The 8.4 Mag is 1070.3 km (665.1 mi) NNE of Tauranga, Bay of Plenty, New Zealand, and the 7.4 Mag is 1053.4 km (654.6 mi) NNE of Tauranga.https://en.wikipedia.org/wiki/Raoul_Island
 

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  • #17
hutchphd said:
So its the stuff that falls into the ocean. The term underwater slide then seems odd. Good to know..thanks.
no, it's not odd nor unusual. both either stuff sliding into the ocean or an underwater slide ... you can get tsunamis from either

there was an example of a large tsunami on the north coast of New Guinea, PNG some years back where there was a Mw7.0 quake
and a large 15 metre tsunami. Eventually they worked out that the quake had caused a large landslide on the edge of the
continental shelf. This tsunami killed well over 2000 people
let me see if I can find the info ...

1998 Papua New Guinea earthquake - Wikipedia

I remember this quake well, I was in first year geology at university and it was discussed at length
 
  • #18
Astronuc said:
M 7.3 - 174 km NE of Gisborne, New Zealand
  • 2021-03-04 13:27:36 (UTC)
  • 37.563°S 179.444°E
  • 20.8 km depth
@davenn did you catch that one?

Several aftershocks.
https://earthquake.usgs.gov/earthquakes/eventpage/us7000dffl/region-info

what a busy morning. I woke up about 2 am and as I often do when already up is come through to the shack and check the seismograph computer monitor. The quake has happened about an hour earlier

long period ~ 20sec channel (higher gain) ...

210304 1327UT  Mw7.3 E of East Cape NZ zhi.jpg


medium period ~ 10 sec channel lower gain ...

210304 1327UT  Mw7.3 E of East Cape NZ zlo1.jpg
 
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  • #19
The M7.4 and the M8.1 are not directly related to the earlier M7.3 other than being on the same and very long megathrust plate boundary.
This boundary stretches from the Hikurangi Trench in the south ( along and offshore of the east coast of the North Island of NZ) and goes
right up to Fiji region via the Kermadec Trench and the Tongan Trench.
This is a huge subduction zone and with it's high relative plate motions up to 9.5cm/yr, it sports some of the deepest earthquake of anywhere
in the world,

Both these events are subduction/thrust quakes. The M7.4 foreshock was down dip(making it deeper) and a bit further to the west from the M8.1.
The USGS have stated that the rupture zone of the M8.1 was approx. 175km along strike and approx. 75 km down dip. I have yet to see
any comments on the amount of slip offset that occurred.

My seismo display for the 7.4 and 8.1 are completely messed in together and with the earlier 7.3 ... it really looks a mess ...

210304 UT  Mw7.3 E of East Cape NZ, 7.4 and 8.1 Kermadecs zhi.jpg


The lower gain channel is a bit more readable ...

210304 UT  Mw7.3 E of East Cape NZ, 7.4 and 8.1 Kermadecs zlo1.jpg
Dave
 
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  • #20
Here's the screenshot of my seismogram for the last 36 hrs ( up till the time of this post)

Still lots of aftershocks from both locations, but mainly from the Kermadec events
Events from M5.1 to 6.2

210306-7  UT  Mw ashks Kermadecs and E Cape zhi a.jpg
 
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  • #21
davenn said:
Still lots of aftershocks from both locations, but mainly from the Kermadec events
Events from M5.1 to 6.2
I've noticed that. I was wondering about increased activity between Tonga and Fiji, and it seems three quakes of Mag 4+ in the last 24 hours. It's been relatively quiet there until yesterday. Let's see if activity picks up.
 
  • #22
According to the news, there was also a swarm of 20K quakes in Iceland in the past week.
 
  • #24
Astronuc said:
I've noticed that. I was wondering about increased activity between Tonga and Fiji, and it seems three quakes of Mag 4+ in the last 24 hours. It's been relatively quiet there until yesterday. Let's see if activity picks up.
Some activity has picked up in the Tonga-Fiji region, including

M 5.8 - south of the Fiji Islands
  • 2021-03-12 00:03:20 (UTC)
  • 25.158°S 178.394°E
  • 559.0 km depth (but this is very deep).
The areas near Gisborne, NZ (some in the low 5 range) and the Kermadec Islands (mostly low 4 range) are still active. The depths are quite shallow.
 
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  • #25
The last 36 hours of activity from my seismograph
All but 2 events are Kermadec aftershocks. The other two, 1 is from eastern New Guinea, PNG and 1 from off shore of East Cape,
North Island, New Zealand.

I have annotated the gram with info on each recorded quake ...

210313  1405 - 2121UT Mw 5.9 x 2 Kermadecs annot zhi.jpg


There's one very interesting observation on this gram. There are two M5.9 quakes from the Kermadec's.
The one at 1405UT and the one at 2121UT. But look at the huge difference in amplitude! at first thought,
one would think there's been a big error in the magnitude estimates but no, the real reason is because that
first M5.9 at 1405UT was much deeper than the one at 2121UT, 37km compared to 10km.
This shows the significant effect of depth and the generation of surface wavesDave
 
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  • #27
Astronuc said:
(36.7 km) further west from the fault

yes, with location and depth, that would infer that it was down dip in the subduction zone.
One could also almost argue that it was an aftershock of the M7.4
 
  • #28
M 6.0 - Kermadec Islands region
https://earthquake.usgs.gov/earthquakes/eventpage/us6000dzlv/executive
  • 2021-04-07 09:53:28 (UTC)
  • 29.101°S 176.673°W
  • 10.0 km depth
A cluster or small swarm of earthquakes happened this past week near the previous large quake.

5.1 Mag 2021-04-11 22:26:13 (UTC-07:00) 10.0 km
5.0 Mag 2021-04-11 07:40:09 (UTC-07:00) 10.0 km
4.9 Mag 2021-04-10 10:51:32 (UTC-07:00) 346.0 km
4.6 Mag 2021-04-08 05:19:49 (UTC-07:00) 10.0 km
5.3 Mag 2021-04-07 18:00:40 (UTC-07:00) 10.0 km
5.2 Mag 2021-04-07 12:43:00 (UTC-07:00) 10.0 km
5.6 Mag 2021-04-07 11:48:00 (UTC-07:00) 10.0 km
5.2 Mag 2021-04-07 06:34:57 (UTC-07:00) 10.0 km
5.4 Mag 2021-04-07 03:42:05 (UTC-07:00) 10.0 km
5.1 Mag 2021-04-07 03:26:51 (UTC-07:00) 10.0 km
6.0 Mag 2021-04-07 02:53:28 (UTC-07:00) 10.0 km
4.8 Mag 2021-04-06 05:40:26 (UTC-07:00) 10.0 km
5.3 Mag 2021-04-06 03:07:46 (UTC-07:00) 10.0 km
5.7 Mag 2021-04-06 01:16:15 (UTC-07:00) 10.0 km
5.2 Mag 2021-04-06 00:37:22 (UTC-07:00) 10.0 km
 
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  • #29

1. What is the significance of the location of this earthquake?

The location of an earthquake is important because it can give clues about the tectonic plates involved and the potential for future seismic activity in the area. In this case, the earthquake occurred near Gisborne, New Zealand, which is located on the boundary of the Pacific and Australian plates.

2. How large was this earthquake?

This earthquake had a magnitude of 7.3, which is considered a major earthquake. The magnitude scale measures the energy released by an earthquake, with each whole number increase representing a tenfold increase in energy.

3. Was this earthquake felt by people in the area?

Yes, this earthquake was felt by people in the surrounding area. According to reports, it was felt as far away as Auckland, which is about 500 km from the epicenter. The intensity of shaking may have varied depending on the distance from the epicenter and the local geology.

4. Was there any damage or injuries caused by this earthquake?

As of now, there have been no reports of major damage or injuries caused by this earthquake. However, it is still important for authorities to assess the situation and for individuals to take precautions, as aftershocks and other hazards may occur.

5. Is there a risk of a tsunami following this earthquake?

According to the Pacific Tsunami Warning Center, there is no current risk of a tsunami following this earthquake. However, it is always important to stay updated on any potential warnings or advisories from local authorities in case of any changes.

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