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People reported feeling the quake from Dunedin to Auckland.
© GNS
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February 9, 2016 - NEW ZEALAND - A strong 5.7 magnitude earthquake has rocked central New Zealand.
The 1.38pm quake was 35km south-east of St Arnaud, Nelson, at a depth of 65km.
Geonet duty seismologist Anna Kaiser said the shake was felt throughout the upper South Island and lower North Island.
"It was widely felt from Taranaki to Canterbury," she said.
There were also five reports from Auckland and one from Otago.
"It was a decent shake," she said.
"With that level of shaking, it would rattle things around but we wouldn't expect major structural damage."
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| USGS earthquake location. |
People have reported feeling the slow-rolling quake in the lower North Island and upper South Island.
Several people in Wellington have posted about the earthquake online.
"It was pretty big. I was shaken by it," one government department worker said.
Adris Cochrane wrote: "Whoa for a sec I thought it was #auckland
property prices falling, but no, actually, an earthquake in Wellington."
Emergency services say they've had no calls about the earthquake in St Arnaud.
Meanwhile, Red Cross worker Hanna Butler said everyone at the Red Cross headquarters dived under their desks.
Some users say they felt the earthquake quite strongly in Christchurch.
Margery Chilton, who owns St Arnaud House Bed & Breakfast in the
Nelson Lakes, said her two-storey wooden house swayed for about a
minute.
"It wasn't as bad as the earthquake a few months ago but it did sway for a little bit," she said.
"Nothing fell down and there wasn't any damage.
"We've got guests that are out for a walk in the park today, though.
I'll be interested to hear how they got on when they return tonight."
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| USGS shakemap intensity. |
"Strong jolt, room shook," said another Nelson resident.
Steve Smith, who is in South Taranaki, said he felt a "long rolling sensation" for about 30 seconds.
The earthquake was felt in the Parliamentary precinct, where Prime
Minister John Key remarked on it to reporters on his way into the
debating chamber.
One Twitter user made a link between the quake and the first day back at Parliament.
One reader said "felt in Palmerston North, I watched my sideboard doors
open and door swinging. I think I have a shaky house though." -
New Zealand Herald.
Tectonic Summary - Seismotectonics of the Eastern Margin of the Australia Plate
The eastern margin of the Australia plate is one of the most
sesimically active areas of the world due to high rates of convergence
between the Australia and Pacific plates. In the region of New Zealand,
the 3000 km long Australia-Pacific plate boundary extends from south
of Macquarie Island to the southern Kermadec Island chain. It includes
an oceanic transform (the Macquarie Ridge), two oppositely verging
subduction zones (Puysegur and Hikurangi), and a transpressive
continental transform, the Alpine Fault through South Island, New
Zealand.
Since 1900 there have been 15 M7.5+ earthquakes
recorded near New Zealand. Nine of these, and the four largest,
occurred along or near the Macquarie Ridge, including the 1989 M8.2
event on the ridge itself, and the 2004 M8.1 event 200 km to the west
of the plate boundary, reflecting intraplate deformation. The largest
recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay
earthquake, which killed 256 people. The last M7.5+ earthquake along
the Alpine Fault was 170 years ago; studies of the faults' strain
accumulation suggest that similar events are likely to occur again.
North of New Zealand, the Australia-Pacific boundary stretches east of
Tonga and Fiji to 250 km south of Samoa. For 2,200 km the trench is
approximately linear, and includes two segments where old (Greater than 120 Myr)
Pacific oceanic lithosphere rapidly subducts westward (Kermadec and
Tonga). At the northern end of the Tonga trench, the boundary curves
sharply westward and changes along a 700 km-long segment from
trench-normal subduction, to oblique subduction, to a left lateral
transform-like structure.
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| USGS plate tectonics for the region. |
Australia-Pacific convergence rates
increase northward from 60 mm/yr at the southern Kermadec trench to 90
mm/yr at the northern Tonga trench; however, significant back arc
extension (or equivalently, slab rollback) causes the consumption rate
of subducting Pacific lithosphere to be much faster. The spreading rate
in the Havre trough, west of the Kermadec trench, increases northward
from 8 to 20 mm/yr. The southern tip of this spreading center is
propagating into the North Island of New Zealand, rifting it apart. In
the southern Lau Basin, west of the Tonga trench, the spreading rate
increases northward from 60 to 90 mm/yr, and in the northern Lau Basin,
multiple spreading centers result in an extension rate as high as 160
mm/yr. The overall subduction velocity of the Pacific plate is the
vector sum of Australia-Pacific velocity and back arc spreading
velocity: thus it increases northward along the Kermadec trench from 70
to 100 mm/yr, and along the Tonga trench from 150 to 240 mm/yr.
The
Kermadec-Tonga subduction zone generates many large earthquakes on the
interface between the descending Pacific and overriding Australia
plates, within the two plates themselves and, less frequently, near the
outer rise of the Pacific plate east of the trench. Since 1900, 40
M7.5+ earthquakes have been recorded, mostly north of 30°S. However, it
is unclear whether any of the few historic M8+ events that have
occurred close to the plate boundary were underthrusting events on the
plate interface, or were intraplate earthquakes. On September 29, 2009,
one of the largest normal fault (outer rise) earthquakes ever recorded
(M8.1) occurred south of Samoa, 40 km east of the Tonga trench,
generating a tsunami that killed at least 180 people.
Across
the North Fiji Basin and to the west of the Vanuatu Islands, the
Australia plate again subducts eastwards beneath the Pacific, at the
North New Hebrides trench. At the southern end of this trench, east of
the Loyalty Islands, the plate boundary curves east into an oceanic
transform-like structure analogous to the one north of Tonga.
Australia-Pacific convergence rates increase northward from 80 to 90
mm/yr along the North New Hebrides trench, but the Australia plate
consumption rate is increased by extension in the back arc and in the
North Fiji Basin. Back arc spreading occurs at a rate of 50 mm/yr along
most of the subduction zone, except near ~15°S, where the
D'Entrecasteaux ridge intersects the trench and causes localized
compression of 50 mm/yr in the back arc. Therefore, the Australia plate
subduction velocity ranges from 120 mm/yr at the southern end of the
North New Hebrides trench, to 40 mm/yr at the D'Entrecasteaux
ridge-trench intersection, to 170 mm/yr at the northern end of the
trench.
Large earthquakes are common along the North New
Hebrides trench and have mechanisms associated with subduction
tectonics, though occasional strike slip earthquakes occur near the
subduction of the D'Entrecasteaux ridge. Within the subduction zone 34
M7.5+ earthquakes have been recorded since 1900. On October 7, 2009, a
large interplate thrust fault earthquake (M7.6) in the northern North
New Hebrides subduction zone was followed 15 minutes later by an even
larger interplate event (M7.8) 60 km to the north. It is likely that
the first event triggered the second of the so-called earthquake
"doublet".
More information on regional seismicity and tectonics
-
USGS.
