18 Jul 2009

Ground raised by quake

9:14 pm on 18 July 2009

A large area around the epicentre of a powerful earthquake in Fiordland on Wednesday night has risen by up to a metre.

GNS Science says this is a very significant movement.

Seismologist Bill Fry says the rise has been gradual.

"The ground now is in a different location that it was previously. It's moved differing amounts in different places - less than a metre.

"The earthquake started about 30 kilometres below the surface where the two plates are connecting ... and as it was breaking, the ground was breaking upward and toward the south."

He says the breaking up of the ground stopped at a depth of 12km, so there is no surface rupture.

The quake is the largest recorded in the world so far this year.

Dr Fry says a GNS team is in the area looking at how the stress distribution has changed from the initial earthquake, and whether any more are likely.


There have been 16 aftershocks since the 7.8 magnitude quake occurred in Dusky Sound at 9.22pm on Wednesday, at a depth of 12km.

It was followed by another, magnitude 6.1, at 9.41pm, which was at a focal depth of 5km.

Dr Fry says the magnitude of the aftershocks is dropping and they're becoming less frequent.

The latest measured 4.9 on the Richter scale and hit at 1pm on Saturday.

It followed a magnitude 4.5 shock at 8.25am on Saturday, centred 80km west of Te Anau at a focal depth of 10km.

Another, measured at magnitude 5.1, occurred at 4.40am on Saturday, at a focal depth of 12km.

The Earthquake Commission says it has received more than 570 claims over damage caused by the massive quake.

Claims manager Lance Dixon says the commission is setting up a temporary office in Invercargill and hopes to have teams inspecting damaged properties by next Friday.

Previous big quakes

Magnitude 7.8 is the same force as the Hawke's Bay earthquake on 3 February, 1931, and the Murchison earthquake on 17 June, 1929.

The GeoNet website says the Wairarapa earthquake on 23 January, 1855, is the most severe to have been recorded in New Zealand.