'Megathrust' quake once caused NZ tsunami, new study finds

Scientists have uncovered proof that two large 'megathrust" earthquakes rocked central New Zealand in the past 1000 years.

It's only after researchers analysed sediment cores taken from a coastal lake near Blenheim that they found traces of these two previously undetected major earthquakes.

These 'subduction' quakes under the Cook Strait-Marlborough area occurred 520 to 470 years ago and 880 to 800 years ago - the oldest one also causing a three-metre high tsunami in Marlborough.

"The findings are significant in terms of understanding earthquake and tsunami hazards in the lower North Island and upper South Island," lead author Dr Kate Clark said.

For many years, scientists have suspected that the southern part of the Hikurangi Margin could rupture in an earthquake and this is the first proof that this is the case.

Subduction quakes differ from normal quakes as they occur on the under surface of the upper plate where two plates meet, instead of on faults within the upper plate.

They're also responsible for some of the biggest quakes and tsunamis in the world such as the 9.0 Tohoku earthquake and tsunami that hit Japan in March 2011.

The research is outlined in a paper in the Bulletin of the Seismological Society of America, published this week. 

A quake of this nature in Wellington is estimated to cost $13billion, with more than 3500 deaths. Source: 1 NEWS

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