Quake activity not 'unusual'

  • 13/05/2016
Quake activity not 'unusual'

The chance of a magnitude 5 earthquake in Christchurch in the next year is just over 50 percent, according to a new forecast.

"The likelihood of a magnitude 5 or 5.9 is at 57 percent right now, so just as likely to not have a quake there," says GNS seismologist Caroline Little.

"When you go up to large magnitudes, magnitude 6s, it's only 7 percent and extremely unlikely, 1 percent, to get a magnitude 7-plus quake."

An area outside Masterton was the epicentre of three earthquakes which woke and shook residents in the lower North Island yesterday.

A magnitude 4.7 quake hit 20km west of Masterton at a depth of 28km at 7:15am, which GeoNet classified as moderate.

Ms Little says it's inevitable -- New Zealand is on shaky ground.

"Wednesday was definitely a shaky night for much of the country, but if you don't deal with earthquakes every day you forget how frequent they actually are. We get an average of one magnitude 4 earthquake every day of the year, and we get one magnitude 5 every week.

"In Masterton in the last month before these two larger quakes, we had a swarm of earthquakes, very tiny, most of them. Since these larger quakes we've had a few aftershocks of magnitude 4."

But she says Masterton is a very active area of the country, and the activity isn't unusual.

"In the broad scheme of things, we all sit on the same two tectonic plates, and these are colliding and that's what's causing all of these earthquakes and volcanic activity."

Dr Little says the movement is not as simple as your kettle boiling and the pressure being released.

"One quake down in Christchurch didn't cause the quake in Masterton, and they also didn't cause what's happening in Ruapehu and White Island.

"When earthquakes happen it causes some areas the stress drops in some areas, but it also builds up in other areas."