Kaikōura earthquake linked to unrest at Taupō supervolcano

It’s been a question on the minds of geoscientists everywhere: can giant earthquakes trigger eruptions?

Now, it seems 2016′s massive Kaikōura earthquake has provided a vital clue to the answer, with just-published findings linking shaking from the magnitude-7.8 event with unrest at our best-known supervolcano.

One of the major study’s authors, Victoria University seismologist Dr Finn Illsley-Kemp, said the theory of earthquake-induced volcanic activity had long been hard to test – partly because quakes large enough to have such an effect don’t happen too often.

But the Kaikōura event - one of the most complex earthquakes ever observed, involving more than 20 faults - left scientists with a trove of rich data to sift through.

Illsley-Kemp said it meant his team were able to investigate two different types of stress changes within the earth known to affect volcanoes.

“The first comes from permanent movement of the ground - think of the coastal uplift at Kaikōura - and the second comes from the temporary movement of the ground that is caused by the shaking,” he said.

“We were able to clearly show that the response at Taupō volcano must have been caused by that ground shaking - because the stress change from this can travel much larger distances.”

The study, published this month in the journal JGR Solid Earth, began with an intriguing signal detected at one of GeoNet’s GPS stations north of Lake Taupō following the quake.

The epicentre of 2016's Kaikōura Earthquake was located near Culverden - some 500km from Taupō. Photo / GeoNet

When the researchers looked at data from nearby stations, they discovered a pattern of local ground displacement, which modelling eventually linked back to the event.

“The biggest curiosity was the timing of the deformation we were seeing,” said study lead author Jessie Schuler, also of Victoria University.

“It began immediately following the Kaikōura earthquake and lasted for almost two weeks before dying out.”

Having ruled out any other sources, the team thrashed out several theories regarding how different types of stress change could have triggered the unrest.

Eventually, they concluded the deformation had been caused by movement of either magma or a fault - with the catalyst being seismic waves that rippled out from the quake’s Culverden epicentre, some 500km away.

Interestingly, the ground-shaking observed was far stronger than that recorded from similarly sized, similarly distant quakes: namely that same year’s 7.1 Te Araroa quake, and a 7.3 jolt near East Cape in 2021.

Schuler explained that was likely due to the “directionality” of the Kaikōura fault rupture shunting seismic energy towards Taupō.

However, it was less clear why Taupō responded to the big quake, but other volcanoes like Ruapehu seemingly didn’t.

Study author Dr Sigrun Hreinsdottir, of GNS Science, said there appeared no obvious links between Taupō's latest unrest periods, in 2019 and 2022-23, and the 2016 earthquake.

Both those recent bouts of activity were attributed to magma moving about within the enormous caldera volcano, just a few kilometres beneath Lake Taupō.

“This might suggest that the volcano was already primed for unrest when the Kaikōura earthquake took place,” Hreinsdottir said, “and the dynamic stress changes caused by seismic waves traveling up from Kaikōura were enough to trigger movement in Taupō.”

Beneath Lake Taupō lies an enormous caldera volcano - and unrest within the system has now been linked to 2016's Kaikōura earthquake. Photo / Galyna Andrushko

Illsley-Kemp said it’d now be interesting to hunt for possible earthquake links in major eruptions from New Zealand’s ancient past.

“We should now delve into the past, using techniques such as sediment logs, to see whether some of the many eruptions we’ve had in the past happened at the same time as large earthquakes,” he said.

“This would allow us to look at a much longer time-series than we are able to with modern geophysical methods.”

Looking forward, Illsley-Kemp said the new findings showed we shouldn’t necessarily treat earthquakes and volcanoes as two separate natural hazards.

“They can be intrinsically linked,” he said.

“We know that we will have large earthquakes in our future - from sources such as the Hikurangi Subduction Zone and the Alpine Fault - so work should consider whether these earthquake scenarios might cause large stress changes at our many active volcanoes.

“These multiple and cascading hazard scenarios would be highly complex and difficult to manage, but there is a lot of work across multiple agencies to help prepare New Zealand for the future.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.