No way to predict devastating earthquakes

Cracks appeared on East Coast beaches after last week's earthquake. Photo / Ali Rewi

There's no way to tell if a flurry of recent earthquakes which have rattled the country are signs of a big one to come, a seismologist says.

Tremors from a magnitude 5.1 quake close to Marlborough Sounds yesterday morning were felt across central New Zealand.

The 80km-deep earthquake struck off the west coast of the North Island at 10am and was located 50km north of French Pass.

It follows a magnitude 6.7 quake west of the Macquarie Islands, about 1000km south of New Zealand, at a depth of 10km on Friday.

And that one came a week after a 7.1 magnitude strong quake rattled the East Cape of the country. Strong aftershocks continued to be felt in the East Coast and Poverty Bay regions this week.

Christchurch's fatal earthquake of February 2011 followed a relatively severe one in the city just five months earlier in September 2010.

However GNS duty seismologist Caroline Little said there was no pattern to earthquakes and no way to predict when a big one might hit or where.

"There's no such thing as a sign of a big one coming because there's no way to predict when the next big one will be."

In fact yesterday's 5.1 magnitude quake was "par for the course" for New Zealand, Little said.

During there past three years alone New Zealand has recorded 75 earthquakes larger than a magnitude 5.

That was an average of 25 per year or one every two months.

"The thing with earthquakes is they get much more coverage and people remember them much more readily when they happen near populations."

A deep quake was rolling while a shallow earthquake had sharp intensity, shattering the ground above.

Because of that earthquakes were only devastating if the epicentre was close to towns or cities and at a shallow depth.

The February 22 earthquake in Christchurch which killed 185 people was only 5km deep and 10km south-east of the city, striking during the busy lunch hour at a 6.3 magnitude.

Little said Canterbury had not been a region considered to have a high chance of such a devastating earthquake because it was not directly above the major Alpine Fault.

However February 2011 proved quakes could strike anywhere, anytime.

"Sometimes the unlikely quake is the one that actually happens."

Similarly, while Auckland and Northlanders were the least likely to feel an earthquake because they were the furthest away from the tectonic plate boundary, there was still "not a zero chance" it couldn't happen in New Zealand's biggest city.

She said Auckland still experienced four times as many earthquakes as New South Wales.

"So it's still much more active than other parts of the world, but in terms of New Zealand, Auckland and Northland are still pretty inactive."

Yesterday afternoon another earthquake struck near White Island, off the coast of Whakatane in the Eastern Bay of Plenty.

It had a magnitude of 3.1 and a depth of 10km.