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Christchurch CBD is shrouded in dust following the 6.0 magnitude quake on June 13 - Source: Lisa Gane -
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Today's strongly-felt aftershocks were within the range of forecasted aftershocks as modelled by scientists, GNS Science said today.
Two weeks ago GNS Science warned there was a one in four chance of a quake measuring anywhere between 6 and 7 striking Canterbury within the next year.
Seismologist Martin Reyner told TV ONE's Close Up the predictions were based on detailed statistics.
Reyner said after the Darfield and February quakes they looked at the rate in which they were getting aftershocks and used that data to revise their forecast for probability in the future.
"There's a lot of statistics involved and as the sequence develops that gets incorporated."
Reyner said on a world scale this is reasonably unusual "in so far as we're getting quite large aftershocks". He said only one previous quake sequence compares with Canterbury and that was the Waitangi Day quake off the East Cape in 1995.
The structure that ruptured off shore of East Cape is the same as what exists under Christchurch, said Reyner.
"There are some very strong rocks under Christchurch."
The scientist said today's magnitude 6 quake will generate its own aftershock sequence and people can expect magnitude 3s "for months and years to come".
He confirmed there are still aftershocks coming from the original quake, including one of 4.3 early this morning, but he said there is now a concentration at the eastern end around Christchurch.
Statistically this is what we were expecting in the next year, Reyner said, adding that unless the forecast changes dramatically people can expect to continue to feel smaller aftershocks of 3, 4 and even 5 magnitude.
"You still need to be prepared for those," he said.
Kelvin Berryman, manager of the Natural Hazards Research Platform at GNS Science, said this size of event is likely to "rejuvenate aftershock activity at least in the short term".
Berryman said aftershock activity had not moved offshore onto other faults in Pegasus Bay.
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