2 Oct 2018

Research could change way scientists forecast earthquakes

10:21 am on 2 October 2018

Research led by Victoria University may have uncovered a new method for forecasting earthquakes.

earthquake generic

Photo: 123RF

The study looked at the behaviour of the main faultline separating the two tectonic plates that lie under New Zealand.

It found that movement along this faultline caused the bottom of the North Island and the top of the South Island to bend like a piece of elastic and that this caused a cascade of earthquakes around Kaikōura in 2016.

Victoria University's Simon Lamb said looking at the single large faultline rather than the 20 different faultlines that were activated during the quake, could change the way scientists forecast quakes in future.

He said the behaviour of the main faultline was a lot easier to track than the multiple faultlines under the country, many of which could not be seen.

Mr Lamb told Morning Report the driver of earthquakes in New Zealand is a megathrust.

He said New Zealand has a network of survey points monitored by satellites that allows scientists to measure the movement of the landscape very precisely.

"This record allowed us to look very, very precisely at how New Zealand was moving in the two decades, which is when we have the record, before the 2016 Kaikōura earthquake."

Each major fault has its own in-built driver of earthquakes, he said.

"The idea is, with a major fault, if you go deep enough down, the rocks are sufficiently hot that they're slipping past each other all the time, day-by-day.

"But in the near surface part, the fault is stuck, or locked and what happens is eventually the forces in the earth build up and the top part breaks, drawing an earthquake and sort of catches up, if you like, with what's happening deeper down."

He said that view is wrong and the driver of earthquakes in New Zealand is actually nothing to do with the faults we can see on the surface, but is controlled by a megathrust.

"This gigantic fault is slipping all the time, day-by-day, at depth deeper than about 30 kilometres but its shallower depth, it's stuck, or locked. What happens is that deeper slipping motion twists or distorts the overlying stuck part and there's only so much of this twisting and distorting that the earth can take before it breaks."

When it breaks, it shatters like a piece of glass, he said.

Identifying shattering events is key, he said, rather than focussing on individual faults.

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