Group of earthquakes: GNS warns people to be on guard as aftershocks continue

Dozens of aftershocks from Friday’s earthquakes and tsunami warnings are not bad news.

In fact, the activity is in line with the scenario monitoring agency that GNS Science called the most likely.

That is, groups of aftershocks of smaller magnitude than the earthquakes on Friday, which will be less frequent during the next month.

But GNS is warning people to be on guard, as recent activity has still increased the likelihood of something bigger happening.

READ MORE:
* 6.1m ‘moderate’ earthquake reported off the east coast
* After 3 major earthquakes in New Zealand, questions remain as to how they could be linked.
* One step closer to forecasting a massive earthquake in the hikurangi subduction zone

“Obviously, the longer we go without [something larger] “It happens, it’s less likely to happen,” said GNS Science seismologist Matt Gerstenberger.

Three major earthquakes rocked Aotearoa on Friday, triggering tsunami alerts and evacuations for Northland cities and the Bay of Plenty coastline.

The three scenarios

GNS had three possible scenarios for what could happen next.

The possibility of another earthquake of similar size of around magnitude 8.0 is classified as very unlikely.

An even larger earthquake of magnitude 8.5 or greater is classified as extremely unlikely.

So far, the numerous activities fit perfectly into scenario one: aftershocks that disappear over time.

“If anything, it’s even on the lower end of the aftershocks we’d expect. We don’t know for sure, but it’s following that. [scenario one]. “

That means earthquakes like the magnitude 6.1 reported Saturday afternoon are “perfectly expected,” Gerstenberger said.

By early Sunday afternoon, there had been about 185 aftershocks of magnitude 4 or greater in the East Cape area.

One was greater than magnitude 6.

It is more difficult for GNS to record earthquakes in Kermadecs due to the distance, but more would be expected there because it was the site of the most powerful earthquake.

So there would have been more than 37 aftershocks of at least magnitude 4, and four of magnitude 6 and up, that the GNS recorded, Gerstenberger said.

A global seismographic network had recorded 100 of magnitude four and above, but even that won’t be the full picture, he said.

Aftershocks tend to occur in clusters rather than steadily diminishing, Gerstenberger said.

“You get a lot for a while, then they shut up, and then you get a lot for a while.”

“Most of the time, there is nothing bigger than the main impact. That’s what those scenarios show: that there are many earthquakes, but they are all smaller. But there is always some chance that something bigger will happen. “

Scientists are monitoring two separate sequences after Friday’s earthquakes and are still figuring out how they are related.

One is due to the upheaval in the Eastern Cape: the 7.1 magnitude earthquake in the morning.

The other is related to subsequent earthquakes at Kermadecs, which measured magnitudes 7.4 and 8.1.

And tsunamis could be in the mix, too.

Normally, scientists would start to look closely at the possibility when earthquakes are of magnitude 7.1 or 7.2 or more, Gerstenberger said.

“What ultimately matters is displacement, so seafloor displacement … Distance from shore doesn’t really matter because tsunami waves can travel great distances.”

However, there are rare cases of tsunami earthquakes, which are recorded as smaller in magnitude but release enough energy to cause a wave.

And because there is still a greater chance of a larger earthquake or tsunami, Gerstenberger reminded people to be vigilant and remember the message “if it’s long or strong, go away.”