Aftershocks to continue for decades, says GNS

5:43 pm on 6 January 2012

GNS scientists say Canterbury could get aftershocks for decades to come but the chance of another large shake are beginning to recede.

They also dismissed the possibility of a big tsunami from a strong quake.

The scientists on Friday briefed Christchurch City councillors and MPs in Christchurch on the future earthquake risk to the region.

The briefing was organised by Mayor Bob Parker who said he was concerned about rumours following a recent series of quakes.

The meeting was briefly interrupted by two jolts, one a magnitude 5.0.

The first, at 2.19pm, measured magnitude 3.5. It was centred 20km east of Christchurch and was 5km deep.

The second, a minute later, was the larger one, and was centred 10km north-east of the city at a depth of 10km.

That came after a warning from GNS's principal scientist Dr Kelvin Berryman that aftershocks up to 5.0 magnitude could be expected in the city for some weeks to come.

Dr Berryman said the Darfield earthquake in September 2010 sparked a series of tremors, including the more damaging February 2011 aftershock and the most recent quakes just before Christmas.

He says these aftershocks are now understood to be rejuvenation events, each carrying with them a series of aftershocks.

Dr Berryman noted that small aftershocks are still being felt in the Nelson region following the Inungahua earthquake of 1968 but these are so small that nobody notices them.

Tsunami risk low

Dr Berryman also told the meeting there's no risk of a damaging tsunami being generated by an earthquake of up to magnitude 6.0 off the coast of Canterbury.

Although a magnitude 7.0 quake could generate a tsunami, he said there is now a very low likelihood of such a quake striking the region.

According to GNS Science there have been 332 quakes since 23 December - 12 in the past 24 hours.

The scientists believe the greatest tsunami risk to Christchurch would likely be generated by an earthquake in South America, for which the city would have at least 12 hours warning before a wave arrives.