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Christchurch from the Port Hills -
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At least three new active faultlines have been discovered in the Canterbury region.
A range of scientists from GNS Science, Niwa and Canterbury University have been conducting research in Canterbury since the February 22 earthquake. The study aimed to get an understanding of aftershock patterns and where future quakes might occur.
Earlier this week, it was revealed GNS Science had forecast a 23% chance the Canterbury region would be hit by a quake measuring between 6.0 and 7.0 in the next year. There was a 6% chance such a quake would happen in Christchurch.
One fault is at sea, in southern Pegasus Bay, and is considered the greatest risk for a magnitude 6.0 to 7.0 earthquake. However, it is not considered a tsunami risk.
The other fault runs from south Hagley to New Brighton, via Barbadoes St in central Christchurch. Scientists believe the 5.3 magnitude Boxing Day may have originated from that fault.
The other fault, which runs under the Port Hills, is being blamed for the February 22 earthquake, which killed 181 people.
However, the GNS Science research confirms that the Canterbury region has a low fault risk in the long term, with the September and February quakes considered "very rare" occurrences.
The current risk from another large quake in Christchurch is similar to the risk of a quake striking Wellington.
Manager of the natural hazards research platform Kelvin Berryman said most of the faults had their major period of movement 50 million years ago.
"The focus of the investigation is to identify the length, orientation and spatial arrangement of faults in the aftershock zone in Canterbury," Berryman said.
For an earthquake of 6 or greater to be generated, a fault of 10km or more in length is needed.
Berryman said even before the investigation started, it was widely known that there were several dozen active faults within an 80km radius of Christchurch and many were capable of producing a damaging earthquake.
As part of the study, the University of Canterbury, working with the University of Calgary, undertook seismic surveys at four separate areas across Canterbury and in Christchurch City.
The focus was mainly on areas where rich patterns of aftershocks had occurred to identify the bedrock faults that these were occurring on.
Professor Jarg Pettinga, of the University of Canterbury, said the fault structures mostly trended northeast-southwest.
"Cantabrians live in a seismically active area, and finding previously unknown faults that seem to have very long intervals between ruptures won't have significantly increased the level of earthquake hazard in the region," Professor Pettinga said.
Younger faults at Pegasus Bay
In Pegasus Bay, a small number of faults showed evidence of reactivation in the more recent past.
"There are younger fault structures that are active and they are reactivating the older faults," said NIWA principal scientist Philip Barnes.
NIWA principal scientist Dr Philip Barnes said more analysis was needed for scientists to understand just what they were seeing in the seismic data.
This continuing assessment would be conducted in parallel with the evolving aftershock sequence, Dr Barnes said.
The government has paid out $1 million so far for the research and Earthquake Recover Minister Gerry Brownlee say it is taking it very seriously.
"When we've got all the information we'll be able to put together building codes that will make Christchurch one of the safest cities in the world to live in."
- With Fairfax
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