The Tasman Sea, which separates New Zealand from Australia, just got 30 cm narrower.

Credit: Google Maps

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WELLINGTON: A massive 7.8 magnitude earthquake last week moved the south of New Zealand closer to Australia, scientists have discovered.

With the countries separated by the 2,250-kilometre-wide Tasman Sea, the 30 cm closing of the gap in New Zealand's southwest won't make much difference.

But earthquake scientist Ken Gledhill of New Zealand government research body Geological and Nuclear Sciences said the shift illustrated the huge force of the tremor, the biggest in the world so far this year.

"New Zealand just got a little bit bigger"

"Basically, New Zealand just got a little bit bigger is another way to think about it," he said. While the southwest of the South Island moved about 30 cm closer to Australia, the east coast of the island moved only one centimetre westwards, he said.

The biggest quake in New Zealand in 78 years caused only slight damage to buildings and property when it struck the remote southwest Fiordland region of the South Island last Thursday.

A small tsunami was generated by the earthquake, with a tide gauge on the West Coast of New Zealand recording a wave of one metre.

"For a very large earthquake, although it was very widely felt, there were very few areas that were severely shaken," Gledhill said. Aerial inspection of the forested fiords near the quake's epicentre showed few landslips or other signs of damage.

'Subduction thrust rupture'

This was partly because the type of rupture at the boundaries of the Australian and Pacific plates meant the energy from the quake was largely directed westwards towards the sea rather than inland towards the nearest towns.

The type of quake, known as a subduction thrust rupture, also meant the quake produced lower frequency shaking, felt as a rolling motion, rather than sharp jolts which would have caused more damage.

New Zealand frequently suffers earthquakes because it marks the meeting point of the Australian and Pacific continental plates.