A cluster of aftershocks has rattled Christchurch over the last week. It will take decades for Canterbury to return to the level of earthquakes experienced before the September 2010 quake, a GeoNet scientist says.

﻿It will take decades for Canterbury to return to the background level of earthquakes experienced before September 2010, a GeoNet scientist says.

GeoNet duty seismologist Anna Kaiser said the cluster of aftershocks that has rattled Christchurch this week was part of the normal decay pattern for the earthquake sequence that began in September 2010. Christchurch was shaken by a 3.1 magnitude aftershock on Sunday morning, a 4.0 on Saturday afternoon, and a 3.8 and a 4.0 on Tuesday afternoon.

"It will take decades to get back to the relatively low background rate for Canterbury," Kaiser said.

"It is quite normal for an aftershock sequence to decay for a long time before we get back to the background. It is quite normal to see a few clusters."

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"These sorts of small earthquakes are still higher than they were before the Canterbury earthquakes sequence started in 2010. The rates are decreasing and we get them a lot less frequently that we did after the earthquakes, but more than before the sequence started."​

"This is not unusual after such a big sequence as we have had in Canterbury. It is still part of the expected period of aftershock behaviour."

She said the recent aftershocks have not affected the probability of another large earthquake striking the Canterbury region. GeoNet last issued probability figures for Canterbury in September. The probability of one or more earthquakes of between 5.0 and 5.9 magnitude over the next year is 45 per cent, according to the GeoNet figures. The chance of a 6.0 to 6.9 magnitude earthquake is five per cent and the probability of a quake above 7.0 is less than one per cent, the figures state.

"The probabilities of really big earthquakes arriving in Canterbury are falling away and they are not changing rapidly."

"You can never rule out a big earthquake anywhere in New Zealand. There is a long tail to the sequence but the quakes will become more and more infrequent."

The recent aftershocks were an unpleasant reminder of the 2010 and 2011 earthquakes for many Christchurch residents. The hashtag #eqnz was trending on Twitter on Sunday morning.

David Delagarza wrote on the social media site: "Yet another little shake. The marked increase seismic activity in Christchurch in the last week is a bit unnerving."

Moata Tamaira summed up how many Christchurch people felt in a Twitter post: "Yuck. Not enjoying this sudden increase in #eqnz activity."