Quake expert quizzed on 'toxic secrets'

Dr Kelvin Berryman describes the likely pattern of quakes for Canterbury in future years. Photo / Simon Baker

Earthquake experts insist they are not hiding sensitive information that might cause panic as anxious Christchurch residents worry about what may lie ahead.

A forum in Christchurch yesterday attended by city leaders, MPs, scientists and journalists heard that the long sequence of devastating earthquakes stretching back to September 2010 was not unexpected.

Although the quakes were likely to continue - possibly for decades - they appear to be moving offshore, and another serious quake of magnitude 7 or more was seen as very unlikely.

Since the latest spate of quakes that began on December 23, rumours have suggested that scientists were expecting another big quake but were keeping it under wraps.

Christchurch mayor Bob Parker yesterday asked GNS scientist Dr Kelvin Berryman to answer to those who thought there was information so "toxic" it was being kept secret.

Dr Berryman said: "There are a lot of things we don't know, but we are bringing information forward as soon as we do have something that is coherent to say".

The recent spate of quakes did tend to increase the odds of more quakes, but with the latest occurring off Christchurch's coast, there was less potential for damage.

"I think we can guarantee there will still be (magnitude) 5s in the coming months," Dr Berryman said.

"Hopefully they are going to continue to be offshore."

"Christchurch's city has had a lot of earthquake activity and a lot of stress must be released in the ... area, but for Canterbury there may well be an ongoing sequence over a period of a few decades."

The risk of a quake of magnitude 7 or more - such as in September 2010 - was "not zero, but it's low".

Evidence pointed to the quakes since September 2010 being "very rare" in a historical context".

"The sequence is now catching up to the number of quakes expected in the time frame, Dr Berryman said.

While quakes offshore created a small risk of a tsunami, experts stressed that only very large quakes created a serious risk.

A magnitude 7 quake could produce a tidal wave of up up to 2m, but that was still not enough to worry about.

Big quakes much further afield, such as in South America, were more of a concern.

Mr Parker said there was reason to believe the worst of the quakes to strike from beneath Christchurch city were over, and people could take heart from this.

A lighter moment came yesterday when the forum was rocked by a magnitude 5 quake and experts on the speaking panel were asked to pick the strength of it.