Science & Technology

After three major earthquakes off New Zealand, questions remain as to how they relate.

Te Herenga Waka, Professor of Geophysics, by Timothy Stern — Victoria University of Wellington

Martin Gruenzweig / Oneworld Picture / Universal Images Group via Getty Images

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The Kermadec subduction zone in Tonga extends between New Zealand and the south of Samoa.

Sequence of three major offshore earthquakes, including Magnitude 8.1 earthquake near the Kermadec IslandsTriggered Tsunami warning and evacuation Along the east coast of New Zealand this morning.

By early afternoon, the National Emergency Management Agency (NEMA) Although the evacuation order was lifted, people emphasized that they should move away from the beaches and beaches.

Three quakes occurred along all Tonga Kermadek Subduction Zone, Where the Pacific Plate goes under the Australian Plate and then sinks.

This subduction zone is the longest and deepest such system on Earth. It extends approximately 2600km northeast of the East Cape and almost straight to the south of Samoa.

One of the questions seismologists around the world are currently trying to answer is whether three earthquakes are related and whether a previous rupture caused a magnitude 8.1 quake.

Potential links between bursts

The Tonga Kermadek subduction zone ends northeast of the East Cape and becomes the Hikrangi subduction zone. The first magnitude 7.3 rupture occurred at 2:27 am, 174 km from the East Coast, where the Hikrangi and Tonga Kermadek systems merged.

United States Geological Survey Recorded this event 21km deep, not 95km deep First report Proposed in New Zealand. There was an anomalous mechanism in this quake — a component of lateral movement known as strike-slip.

https: // … 1200w, https: // … 1800w, https: // … 754w, https: // … 1508w, https: // … 2262w “sizes =” (min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px “> (statically edited by The Conversation), CC BY-SA

The other two quakes were about 900 km north, but just west of the Tonga Trench, about 56 km deep (6:40 am). Magnitude 7.4 event) And 20km ( Magnitude 8.1 earthquake 8:28 am). These later events had a thrust or compression mechanism in which one body of rock compresses against another body of rock during an earthquake, sliding over it and sliding up.

This is expected in a subduction zone where one structural plate slides under another and causes a collision, which causes compression.

As the Pacific plate begins to slide under the Australian plate, it begins at a shallow angle, then bends along a curved orbit, and finally falls at a very steep (60 degree) angle. But when it is at a shallow level, it sinks only at, for example, 10-20 degrees, increasing friction with the upper (Australia) plate. This is usually where these big earthquakes occur.

Trigger sequence

Magnitude 8 earthquakes in these subduction zone settings are not uncommon. In fact, earthquakes up to magnitude 9 can occur. Japan’s 2011 off the Pacific coast of Tohoku Earthquake, Submarine earthquake off Sumatra 2004 Indian Ocean TsunamiThere was an earthquake in Alaska in 1964 and in Chile in 1960.

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What is interesting about this sequence off New Zealand is whether or how the ruptures are related to each other. Indeed, the first of the two later earthquakes, which are within tens of kilometers of each other, can be considered a foreshock, followed by a major magnitude 8.1 impact. But was the earliest 2:27 am earthquake north of the East Cape related?

In general, seismologists believe that a distance of 1000 km is too far to disturb the ground and cause another rupture, even with a magnitude 7.4 rupture. However, there is increasing debate that the Earth is critically stressed to the point where even the slightest tweak can trigger another event in the setting of plate tectonics.

After the 2004 Sumatran orangutan earthquake, scientists said it was Caused another earthquake One hour later, it is about 11,000 km away in Alaska. But in this case, they were small events following a major triggering earthquake.

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It is also interesting that a large earthquake occurred off the Kermadec Islands in the past. In 1976, a magnitude 7.7 event was followed by a magnitude 8 event 51 minutes later. This reflects what we saw today.

Both events in 1976 were thought to be huge earthquakes like today’s shock. Then, in 1986, at a depth of 45 km, a magnitude 7.7 event showed both thrust and lateral strike-slip motion. The interpretation of this event was that it happened within the subducting and bending Pacific plate, not the plate interface event.

This can explain the second quake this morning, as it appears to be 56km deep within the Pacific Plate. You have to wait until the final depth and mechanism are resolved.


Timothy Stern does not work, consult, own shares, or receive funding for any company or organization that would benefit from this article.

Originally published conversation..

After three major earthquakes off New Zealand, questions remain as to how they relate. After three major earthquakes off New Zealand, questions remain as to how they relate.

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