Geonet revises Canterbury quake - it's on the West Coast
PAUL GORMAN, MYLES HUME AND AIMEE GULLIVER
Geonet map showing the revised location of the mag-6.0 quake, west of Arthurs Pass, and hundreds of felt reports.
A major magnitude 6.0 quake to hit the South Island at 6.48am today was centred about 30km west of Arthurs Pass, not in Canterbury.
About 10.20am, seismologists issued a dramatic revision of the location and magnitude of the earthquake which jolted thousands from their beds.
GNS Science spokesman John Callan said latest information showed the quake was of magnitude 6.0, not the 6.4 earlier reported, and centred about 30km west of Arthurs Pass, close to where seismic equipment originally suggested.
It was 5km deep.
Earlier, the "severe" earthquake was thought to be centred 35 kilometres north of Methven, on the western edge of the Canterbury Plains, at 10km deep.
Trains from Christchurch to the West Coast and down to Oamaru have been cancelled and dozens of aftershocks recorded.
However, there have been no reports of significant damage.
How did seismologists get it wrong?
Geonet duty seismologist John Ristau admitted there had been a dramatic change to the reported epicentre.
He explained that more than 100 seismometers across the country would have determined the initial reading, but after such large quakes Geonet usually reviewed this.
They focused on 30 to 40 South Island based seismometers, closer to the epicentre, to generate a more accurate reading, he said.
"Because of the big difference in the structure of the earth between the North Island and South Island, if you include North Island stations for South Island earthquakes it can sometimes really throw off the system as far as the location and the magnitude.
"Normally when we review, things don't change as dramatically as it did in this case, but unfortunately you can get some dramatic changes."
Earthquake not caused by Alpine Fault
Geonet scientist Caroline Little said it was likely the earthquake was caused by a previously unknown fault.
"It's still 20 kilometres away from the Alpine Fault, so it won't be that one," she said.
"There are lots of earthquakes around there every year and we don't attribute every earthquake to a fault, we just know that that's a zone prone to earthquakes."
Magnitude six earthquakes were just as likely to be caused by an unknown fault as one that had been previously identified, Little said.
The initial shake was followed by a swarm of more than 20 aftershocks in the area ranging in magnitude from 3.2 to 4.2, centred about 30km west of Arthurs Pass.
Geonet duty seismologist John Ristau said the aftershocks would "probably go on for a while" and "it wouldn't be surprising" to have an aftershock above magnitude 5.
The Arthur's Pass area had had earthquakes of a similar size in the last 100 years or so, Ristau said.
Train services suspended for checks
KiwiRail suspended all services in the area, including the TranzAlpine train from Christchurch to Greymouth and all freight services, while the tracks were checked. Buses were provided for TranzAlpine passengers.
Rail lines were also closed between Oamaru and Christchurch, Oaro and Christchurch, along with the Midland and Stillwater lines for track inspections.
The Coastal Pacific service was running although this had been delayed about 90 minutes.
TranzAlpine passenger Paul Blake said KiwiRail staff were helpful, and he had been offered a choice of a refund, rebooking, or a replacement bus journey.
Meanwhile, a New Zealand Transport Agency spokeswoman said inspections had found no damage on State Highway 77, near Methven, State Highway 73 through Arthur's Pass, and State Highway 6 on the West Coast.
St John had no quake-related call-outs. And no reports of damage or injury were made to the West Coast or Darfield police, nor to the Methven fire station.
The 67km Rangitata Diversion Race, which serves about 500 farms, also appeared undamaged.
Cantabrians report 'scary' shake but no damage
Geonet had about 3000 reports of people having felt the earthquake as far south as Mandeville, in Southland, to the central North Island.
At Lake Coleridge homestay owner Peter Low said the quake felt "pretty severe".
"It wasn't like the last big one we had, which was a real rise and fall job. This was more of a spongy shake, but it was pretty severe."
However, Lake Coleridge Lodge owner Toni Barlow said the quake felt "very ordinary". "Nothing has moved at our lodge and we have had a phone around the village and everyone is saying the same thing.
"It was no different to us than the aftershocks after the big Christchurch earthquake."
Leonie Donald, who works for Methven Motor Services, said the quake appeared to cause no damage in the town and they were getting on with the day as normal.
"It wasn't very severe . . . nothing's fallen off the shelves."
Arthur's Pass Store and Cafe manager Debbie Stewart had not heard or seen reports of damage or injury, and the store itself was intact.
"It was a really good shake, enough to make your heart go," she said. But nothing had fallen from shelves.
Carole Giles, of Hawarden, north Canterbury, said she felt "a sharp shaking for three to five seconds then several rolling sensations" for about five minutes.
"Lots of creaking noises in the house and several things shaking," she said.
Reader Danyal Taylor is staying in Castle Hill, about 15km from the epicentre. She reported no damage.
"We were in bed when it happened and it lasted for about 15-20 seconds," she said.
Aaron Tily of Ashburton said it was "a scary one". "We haven't felt anything like that for quite some time," he said.
"I was day-dreaming at the time and felt something really sharp for a couple of seconds. Nothing broke but scared me and the cat quite a bit."
West Coast cafes may suffer loss of business
The cancellation of the TranzAlpine train between Christchurch and Greymouth was likely to be the biggest impact of the earthquake on the West Coast.
Robert Harris owner Julie McGeady said there was no damage or items falling from shelves but the axing of the TranzAlpine would "absolutely affect us".
As one of the closest cafes to the train station, "we can get 80 odd people off the train, if not more," McGeady said.
DP1 Cafe manager Sarah Burdon said she was woken by the shake but the loss of trade from the cancellation of the TranzAlpine could mean "a lot less stress".
Twitter lights up with quake reports
One Christchurch-based Twitter user said the quake "felt like the house was at sea".
That #eqnz just felt like the house was at sea (in Christchurch) — The Queen of Cobden (@QueenofCobden) January 5, 2015 Another Twitter user reported feeling the quake in Franz Josef.
Felt that wobble in Franz Josef #eqnz — Mark English (@MarkEnglish) January 5, 2015 Cheryl Bernstein said it was an "extraordinary swaying earthquake".
West of Arthur's Pass, apparently. I've never felt one quite like that before. #eqnz — CherylBernstein (@CherylBernstein) January 5, 2015 Karen Foreman-Brown said the quake was large enough to have set off alarms in her neighbourhood.
On the Stuff.co.nz Facebook page, Jackie Cooper said she felt the earthquake in Golden Bay at the top of the island, and Dale Wedlock said he felt it in Dunedin.
Don Gutsell said he had photos swinging at his house in Temuka.
That shake set off neighbourhood alarms #eqnz — Karen Foreman-Brown (@serenity22) January 5, 2015 --
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