Cantabrians have been shaken by three strong aftershocks today, with the latest a magnitude 4.5 just after 5pm.
The first, and largest, was a magnitude-5.5 that struck near Rolleston at 9.09am at a depth of 15 kilometres.
The Canterbury Quake Live website reported that shake was the sixth largest since September 4's magnitude-7.1 quake.
It was followed by a magnitude-3.8 tremor at 11.41am. This 10km-deep shake was centred on Weedons, about 4km from Rolleston.
The latest one, a magnitude 4.5, struck near Rolleston again at 5.04pm at a depth of 10km.
GNS Science duty seismologist Brian Ferris said the magnitude-5.5 aftershock was "within the forecast we expected".
It was not a sign of "anything big" to come, but it was likely that small aftershocks would follow today's quake.
"It's possible there'll be an increase in activity in the area, but it's unlikely anything as big will occur," he said.
RED ZONE MOVEMENT
A Christchurch Earthquake Recovery Authority (Cera) spokesman said indicator buildings in Christchurch's red zone experienced a "small amount of movement".
The eight indicator buildings, of differing construction types, are located throughout the CBD. Any faults in the buildings are monitored for changes after each significant aftershock.
The spokesman said today's aftershock had not caused "any great concerns" and CERA had not restricted access to the red zone.
"There's no immediate danger, but we are keeping an eye on it," he said.
Regular inspections of the indicator buildings and work in the red zone would continue as normal, he said.
Fay Burson, manager of bottle store Henry's in Rolleston, said she probably lost more stock during today's shake than in February's magnitude-6.3.
"It was a very severe initial jolt after a bit of a lull."
The shop was still open.
Burson said September's earthquake was much worse.
"We had minor damage, nothing compared to our first one of course."
The Warehouse in Rolleston has closed for a few hours after stock fell off shelves during the shake.
Stockroom worker Jo Edmond said she was feeling "a little bit nervous".
The store still had power but would be closed for a few hours while staff cleaned up, she said.
"The store's a bit of a mess. There's a lot of glass, but nothing too bad."
She said there were not many customers in the store at the time, and off-duty staff had come in to help with the cleanup.
Damaged and fallen stock saw New World Rolleston close immediately after the tremor, owner Roy Bridgman said.
However, the store was ready to reopen shortly before 11am.
"Our staff are all fine. We just cleaned the shop straight away."
Bridgman said he was at home getting ready for work when the aftershock hit.
"You never get used to it, but it's a fact of life and you just have to carry on."
Westfield Riccarton public relations manager Deb McGhie said most of the mall was still closed at the time of the aftershock because of the public holiday.
The Pak 'n Save supermarket was open and "lost only about half a dozen shampoo bottles".
McGhie said engineers were monitoring the building, but there were no concerns about damage.
Retailers were told they could close or evacuate, but everyone had opened as normal, she said.
FEW KNOWN PROBLEMS
A Christchurch City Council spokeswoman said no "matters of concern" had been reported after this morning's aftershock.
A water outage in Cashmere last night was unrelated to today's quake, and water had been restored to the area this morning, she said.
A Fire Service shift manager said two alarms were activated after the shake, but both were false alarms.
"We had no calls from the public. I think people are now going and checking everything before they call, whereas before they'd just call us straight away," he said.
Police said there had been no reports of damage.
Meanwhile, an unrelated power outage cut electricity in parts of Fendalton and Ilam for just over an hour this morning.
A cable fault cut power at 8.23am, but repair crews had it restored by 9.36am.
Spectators and players at a rugby tournament for four to 16 year-olds in Rolleston saw the ground "roll" during this morning's aftershock.
The tournament, involving 42 teams, kicked off just before the tremor struck, but it did not stop the players for long, Rolleston Rugby Club president David Egan said.
"Everyone stopped and looked, then carried on. Everyone's come to expect them now."
Some people reported seeing the jolt hit the ground, he said.
"They could see it rolling, heading towards the clubhouse. It hit the car park first and lifted some vehicles off the ground, then hit the clubhouse."
Egan said a "few cans and bottles" fell over inside the clubhouse, but there was no other damage.
FELT AROUND SOUTH ISLAND
Twitter users across Christchurch reported feeling the quake, with some saying it had knocked items off shelves.
People reported feeling the quake in Hawarden, Akaroa and as far away as Dunedin and Nelson.
Colleen Simpson, in St Albans, said: "Our cupboards all opened and water sloshed out of the sink and fish tank."
Ellen Martin, 20, of Dunedin, said the aftershock was "scary".
She was visiting family in Rolleston and said several ornaments were broken in the house during the quake.
She felt the February 22 quake in Dunedin but said she was "not used" to feeling tremors like this.
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- The Press