New Zealand made the headlines this time last year after a 7.8M quake rocked both the North and South Islands. For such a powerful tremor, it was lucky only a handful of people were killed – but geoscientists are now warning that the pieces are in place for the next catastrophe.
“One thing about reflecting on from the Kaik?ura earthquake is we don't want people to think this is the big one,” GNS scientist Dr Ursula Cochran told a gathering of scientists in Blenheim earlier this month, per Stuff.co.nz.
New Zealand’s so-called “big one”, a potential 9.0M tremor, is still on its way.
The world’s most powerful earthquakes always occur on these subduction zones. The 2011 Tohoku earthquake and tsunami in Japan was a devastating recent example of this, but it appears not much media attention is being given to various subduction zones around the world.
Although the likelihood of a powerful tremor occurring along the San Andreas Fault in the next 30 years is essentially a dead certainty, it’s actually the Pacific Northwest you should watch out for, where the subduction of one plate under the North American plate is building up a lot of stress.
The Hikurangi subduction zone off the eastern seaboard of New Zealand’s North Island is in a similar situation. Here, the oceanic Hikurangi Plateau is sinking beneath the continental crust of the Indo-Australian plate.
The friction between these colossal pieces of crust builds up stress, and occasionally it’s released during earthquakes of varying intensity. The 7.8M Kaik?ura earthquake in November 2016 took place along the southernmost part of the Hikurangi subduction zone.
Although it’s debated how much the Hikurangi subduction zone had to do with the earthquake, geologists agree that this part of the fault network is now active. Initially, most suspected the southern end was pretty rigidly stuck, but the quake changed all that. It’s moving, and it’s building up stress.
When it ruptures, it could produce a powerful, potentially record-breaking megathrust earthquake. Its geographical position means that it has the potential to generate a powerful and devastating tsunami too, one that would take only seven minutes to reach the North Island, and a little longer to hit the northern South Island.
“We need to think Japan 2011 basically, because if our whole plate boundary ruptured it would be a magnitude 9 earthquake,” Cochran added. She later clarified that quakes reaching 8.0M are known from the geological record; a 9.0M is theoretically possible.
At present, no-one can say when such an event will occur, nor whether the entire fault will slip all at once – but it’s certainly something the authorities need to be aware of.
“Don't be scared, be prepared,” Cochran told the New Zealand Herald.