Quakes just 'business as usual'

02:31, Jul 08 2013

Two sharp jolts that shook parts of the country in recent days have been described as just "business as usual".

A magnitude-4.9 quake shook up parts of Hawke's Bay about 10am today. It was centred 25 kilometres northeast of Waipukurau at a depth of 31km.

Five people in Hastings and one in Napier reported effects of the quake that were classed as "strong".

Earthquakes with that intensity can make it difficult to walk steadily. Objects can fall from walls and shelves, glassware and crockery break, and some slight non-structural damage can be done to buildings.

"It's a reasonably sized earthquake. It was a bit of a deep earthquake ... so it's not quite as serious," GNS Science duty seismologist John Ristau said.

"There's nothing unusual except it's a bit bigger than we normally get."

Today's quake had no connection to the magnitude-5.3 quake that shook Fiordland on Thursday, other than that both happened where two tectonic plates were colliding.

The Fiordland quake struck about 7.40am and was centred at a depth of 5km just off the coast of Fiordland 25km northwest of Milford Sound.

GeoNet classed it as "severe" but the area where it happened is remote, and the people who reported feeling it live some distance away and listed damage that amounted to no more than that expected in a "moderate" shake.

Ristau said the Pacific Plate, off the east coast of the North Island, was pushing under the Australian Plate which the North Island sat on.

In Fiordland, the situation was reversed with the Australian Plate pushing under the Pacific Plate.

"Fiordland is probably the most seismically reactive area in New Zealand," he said. "No-one lives out there, so for the most part these big earthquakes tend to go unnoticed."

Aftershocks from the Fiordland quake, the largest of which was magnitude-4, had pretty much died out. A 2.4-magnitude quake in Hawke's Bay at 10.50am today may have been an aftershock, but typically the deeper quakes did not generate much in the way of aftershocks.

There was nothing unusual about earthquake activity in recent weeks, Ristau said. "It's business as usual."

Recent quakes included a 3.8-magnitude in Waikato about 6.40am today, 3.7 off Mahia Peninsula about 6.15am, 3.5 in Christchurch early yesterday, and 3.5 off the northwestern tip of the South Island about 8.20pm on Friday.

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