PLANETARY TREMORS: Massive Shift In Alpine Fault In New Zealand, Much More Than Previously Thought - New Research!

The Alpine Fault, which runs up the spine of the South Island, has ruptured five times in the past 1100 years -
producing an earthquake of between magnitude 7 and 8 each time. © GNS Science

March 8, 2016 - NEW ZEALAND - The Alpine Fault has moved much more than previously thought, and more than any other known fault on land in the world, new research shows.

In the past 25 million years, the two sides of the South Island have shifted more than 700 kilometres relative to each other along the Alpine Fault. That is 250km more than previously thought.

The full extent of the movement was masked because the rocks first moved 250km in one direction, then went back the other way - retracing the first 250km and adding a further 450km.

GNS Science earthquake geologist Robert Langridge has been studying why the Alpine Fault is so susceptible to earthquakes - it's since been discovered that it may be the world's fastest-moving known fault line.

The extent of the movement was worked out by researchers from Victoria University and GNS Science, with the findings published in the American Geophysical Union journal G-Cubed.

GNS Science earthquake geologist Robert Langridge studying layers in the trench across the Alpine Fault at Springs Junction. New research has found that the
fault line may be the world's fastest-moving, having shifted around 700km in 25 million years. © Joanne Carroll/Fairfax NZ

"I don't think anybody in their wildest dreams would have thought that displacements on the fault could be so large, and also change direction so dramatically through time," Associate Professor Dr Simon Lamb, from Victoria's School of Geography, Environment and Earth Sciences, said.

The researchers made the discovery by looking at geological maps together with studies of the direction of magnetisation in the rocks.

The finding underscored the fact the Alpine Fault was the big seismic hazard in the South Island and had been for a "very, very long time", Lamb said.

The findings may have implications for why the Alpine Fault is so prone to earthquakes.© GNS Science

Other faults in central and southern parts of the South Island had played only a small role in the movement of the tectonic plates.

The next largest known fault displacement on land was on the Altyn Tagh Fault in Tibet, with a total movement of about 475km.

The new theory about the Alpine Fault was a major shift in thinking and the researchers had needed to provide convincing arguments to get it published.

GNS Science earthquake geologists studying layers in the trench across the Alpine Fault at Springs Junction.© GNS Science

The idea occurred to him only about six months ago, Lamb said. "I was calculating the motion of the tectonic plates through New Zealand and realised they were so much bigger than the movement everyone was saying had taken place on the Alpine Fault."

His advantage was that coming from the UK he wasn't wedded to a particular way of thinking about it.

"We put together this team of people who came at it from lots of different directions to make sure this was right, that we hadn't made some terrible mistake and missed something." The idea was exciting but it was followed by a large amount of work. "You spend a lot of time checking. You have to go through an enormous amount of information to look at what other people have discovered. You do a lot of testing. In you mind you play devil's advocate," Lamb said.

"It will be interesting to see what the reception is."

The Alpine Fault started as part of the break-up of the supercontinent Gondwana, with New Zealand starting to drift away from Antarctica about 80 million years ago.

That resulted in about 250km of movement along the Alpine Fault but in the opposite direction to the way the fault is moving today. Then "nothing" happened for tens of millions of years, Lamb said.

About 25 million years ago a new plate boundary formed and the Pacific Plate and Australian Plate started moving relative to each other "in a big way".

"That's the situation today. You have the Alpine Fault breaking up this fragment of continent that split away from Gondwana," Lamb said.

It had been thought movement along the Alpine Fault was getting faster. "Basically what we showed was that from the moment the Alpine Fault started to move in the direction it's moving today it more or less moved at the same rate." That was an average speed of about 3cm a year. - Stuff.

PLANETARY TREMORS: Strong Magnitude 6.6 Temblor Shake Near The Kermadec Islands Triggering "GHOST QUAKES" In North Island, New Zeland - But Why?!

Tuesday's earthquake was centred near the Kermadec's Raoul Island, about 1000km northeast of New Zealand.© Massey University

February 2, 2016 - NEW ZEALAND - The magnitude 6.6 quake that struck off the coast of the North Island on Tuesday was widely felt and triggered false reports of shakes in New Zealand.

It is not uncommon for earthquakes to confuse seismic readings as energy from tremors travels large distances.

These "ghost quakes" register as local earthquakes when the GNS Science system starts to receive data.

Seismic graphs show the earthquake waves at 8am on Tuesday detected by the northernmost seismographs.© John Ristau

Let's dive right in to the world of ghost earthquakes.

What happened on Tuesday?

A large magnitude 6.6 quake centres about 850 kilometres north of Whakatane at a depth of 360km.

The epicentre was near the Kermadec Islands and the Kermadec Trench.

The location of the quake. Deep quakes off the coast can be initially recorded as multiple quakes.© USGS

The United States Geological Survey located the earthquake 120km north-northwest of a barren outcrop known as L'Esperance Rock.

Below the North Island, the Pacific plate is subducting beneath the Australian plate, which causes deeper quakes.© GeoNet

ell me more about this part of the Pacific.

The trench is the fifth deepest point of the world's oceans.

It marks the point where the Australian plate meets the Pacific plate.

A national seismic trace shows the earthquake detected progressively, from Raoul Island southwards.© GNS Science

Geographically, the entire region is one of the most seismically active areas in the world.

So, about all that shaking people "felt" in New Zealand.

A still from the Raoul Island webcam on Tuesday at 9.20am.© GNS Science

New Zealanders felt the quake's energy, but it wasn't in New Zealand.

Seismographs interpreted the waves as locally sourced and triggered alerts for the North Island.

"Ghost" quakes sometimes appear on the seismic monitoring system, the GeoNet array of around 200 seismograms dotted around New Zealand, after a large regional earthquake.

Magnitude 6.6 is a big shake and has the potential to cause a disaster.

Sensitive equipment picks up the seismic waves created by earthquakes. Equipment gets confused and pushes out an earthquake alert interpreted as locally sourced to the public, when the shake could be hundreds of kilometres away.

As in this case?

Yes, the earthquake was around 1000km away and deep.

This is all a bit confusing.

It's simple.

As the seismic waves travelled south from the source they are picked up progressively by detectors.

First Raoul Island, which has a webcam by the way, picked up the earthquake then the network detected the waves as they quickly moved southwards.

The "ghost" or "false" quakes, reported on Tuesday as three severe quakes in the Bay of Plenty region, were removed from the GeoNet alert system after initial reports.

This kind of thing has happened before.

In 2013, a quake near the location of Tuesday's shake triggered ghost earthquake readings in New Zealand.

Why don't scientists wait to confirm an earthquake's location?

In short, it's important to get information and data out to the public quickly.

As soon as readings start coming in from the seismic network that information is automatically publicly notified.

Later, once GNS Science review data, they can revise the reported magnitude and pinpoint the precise location.

Let's get technical shall we?

OK, it's all about different types of seismic waves, known as P-waves and S-waves, and the types of detection equipment.

P stands for primary waves, S for secondary.

Broadly, the equipment confuses the secondary waves for primary shaking, hence the three severe shakes initially reported by GeoNet and felt by New Zealanders.

GNS seismologist Dr John Ristau says:

"People actually felt the quake. It was quite deep.

"Our automatic system, generally, for 99 per cent of the time it actually works quite well.

"We know there's a problem when we have large earthquakes north of the North Island, particularly when they are deep.

"Our automatic system gets fooled.

"Primary waves are the fastest. That triggers the system. Then you have the secondary waves. The S-waves come in well defined...so the automatic system gets fooled into thinking it's another earthquake."

Can scientists do anything about the confusion?

The current system is the best available.

Ristau says GNS Science would rather have the system detect earthquakes as false than re-calibrate it and risk failing to detect a locally-sourced shake.

Plus, it's important to get information out to the public as quickly as possible in New Zealand and the Pacific.

Seismograms are extremely sensitive aren't they?

They can pick up wind and traffic noise, so it's no surprise when they detect tremors from earthquakes hundreds, or even thousands, of kilometres away.

They picked up the Foo Fighters blasting Auckland in 2011, remember?

That area of the ocean sounds interesting.

The Kermadec Islands and the surrounding area lie within a marine sanctuary created in 2015.

Once fully enacted as a reserve by the Government in 2016, the sanctuary will be one of the largest and most protected marine regions in the world.

It's even possible to visit, although you'll need a permit. - Stuff.

PLANETARY TREMORS: Very Strong 6.6 Magnitude Earthquake Strikes North Of New Zealand - Geonet! [MAPS + TECTONIC SUMMARY]

USGS earthquake location.

February 2, 2016 - NEW ZEALAND - A 6.6 magnitude earthquake 1100km off the North Island was responsible for the tremors that shook New Zealanders this morning.

Geonet seismologist John Ristau said the tremors felt in Bay of Plenty, Tararua and Canterbury were not official earthquakes.

There had been reports that a 5.3 magnitude quake was recorded 35 km south of Murupara and that 5.0 magnitude quake struck 20 km north west of Pongaroa.

A third quake was said to have hit 15km south-west of Amberley.

USGS shakemap intensity.

The shakes weren't official earthquakes but ripple effects of a 6.6. earthquake near Raoul Island.

Geonet received more than 500 reports of people who had felt shakes, Mr Ristau said.

There would be few aftershocks because the earthquake was so deep, he said.

Old Shaky Isles living up to its reputation! A few #eqnz in the past 15 mins pic.twitter.com/BdE1p26aCS

— Paola Brett (@paolabrett) February 1, 2016

Several people have reported feeling the quakes on social media, in areas including Bay of Plenty and Wellington.

Fire Service and police northern communications have received no reports of damage.

A spokesman for the Murupara police said he was outside when the earthquake was recorded as happening and he didn't feel a thing. He said there had been no calls from members of the public.

A woman spoken to at Murupara Area School was also surprised to hear reports of a quake - saying she didn't feel anything and nobody at the school had felt the quake. - New Zealand Herald.

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.

USGS plate tectonics for the region.

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.

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.

PLANETARY TREMORS: Strong Magnitude 5.1 Earthquake Shakes Lower North Island, New Zealand- Geonet! [MAPS + TECTONIC SUMMARY]

The earthquake was felt throughout the North Island. © Keith Lynch (CPL)

January 4, 2016 - NEW ZEALAND - An "short, sharp shake" has been felt throughout the lower North Island, with a lighter earthquake coming two hours later.

Geonet received reports from 865 people that had felt the 5.1 magnitude quake with reports from people who have felt it, from as far as Ohakune and Hawera.

The quake was centred 25 kilometres east of Pongaroa, in the Tararua district, at a depth of 25km, hitting at 1.07pm.

Bit of a shudder here at Paekakariki - est 20 seconds duration #eqnz
— Jesse Easton (@jesterabi) January 4, 2016

Tararua District councillor Shirley Hull was at her Pahiatua home with family when she felt the quake hit.

She said Pongaroa's "short, sharp shake" left their light swaying.

"They seem to be getting a few these days... [we have] just got to make sure that everybody's OK."

Nasty lunchtime shake here in Palmerston North. #eqnz
— Gerry le Roux (@GerryleRoux) January 4, 2016

Natalie Raynel said she felt a similar shake in Dannevirke, but it was "not too bad".

Folker Liebenow, who lives between Waipukurau and Hastings, said he felt the quake but there was no damage.

He said they felt every one of the quakes that hit Pongaroa, and by those standards it was "moderately strong".

Geonet classified the earthquake as 'strong'.

The second earthquake hit 40km east of Pongaroa, with an intensity of 4.1 magnitude, at 3.10pm.

With a depth of 35km, the earthquake was classified as 'light'. - Stuff.

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.

USGS plate tectonics for the region.

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.

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.

PLANETARY TREMORS: Strong Magnitude 5.8 Earthquake Strikes Near New Zealand's Coast - USGS! [MAPS + TECTONIC SUMMARY]

USGS earthquake location.

January 2, 2016 - NEW ZEALAND - A 5.8-magnitude earthquake on Friday struck New Zealand's coast, the United States Geological Survey (USGS) said.

Tremors were registered at 15:02 GMT.

The epicenter was located about 50 miles north-east of Raoul Island at the depth of approximately 61 miles.

USGS shakemap intensity.

No information about the damage or casualties was immediately available.

Parts of New Zealand lie on the so-called Ring of Fire, a horseshoe-shaped string of volcanoes around the Pacific Rim, where about 90 percent of the world's quakes occur. - Sputnik.

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.

USGS plate tectonics for the region.

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.

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.

PLANETARY TREMORS: The Seismic Hazards Of The Hikurangi Margin - Geologists Warn Mega-Quake And Tsunami Could Hit Central New Zealand!

The study area was salt marsh flats on the edge of Big Lagoon near Blenheim.  Mark Cornell

May 19, 2015 - NEW ZEALAND - Scientists finally have proof that central New Zealand could be ticking down to a highly damaging "megathrust" earthquake.

Earlier research has suggested the seabed between the Wairarapa and Marlborough is capable of generating magnitude 7-plus quakes.

Now researchers have found solid geological evidence that an area off the coast of Wairarapa and fringing Cook Strait causes "megathrust" quakes and tsunami similar to, but probably smaller than, the devastating magnitude 9.0 March 2011 event in Japan.

The work, out Tuesday morning, highlights the active threat the southern Hikurangi margin - where the Pacific Plate is being dragged down below the Australian Plate - poses to life and livelihood from Hawke's Bay south to the Wairarapa, Wellington and Marlborough.

The Alpine Fault, which extends further south from that plate boundary, is also a hazardous feature that will generate a magnitude 8 quake when it ruptures, possibly some time in the next 50 to 100 years.

To look for evidence of past earthquakes on the margin, the researchers performed a painstaking examination of the geologic layers contained within
a salt marsh at Big Lagoon in the southeastern Wairau River valley on South Island.   GNS SCIENCE

 

The scientists, from GNS Science, the University of Texas and Geomarine Research, have calculated that in the past 1000 years two subduction quakes of at least magnitude 7 occurred – one between about 880 to 800 years ago and the other between 520 and 470 years ago."This is the first evidence that the southern Hikurangi margin ruptures in large (7-7.9) to great (8+) earthquakes, and the relatively short time interval between the two events has significant implications for seismic hazard in New Zealand," they said in Tuesday's Bulletin of the Seismological Society of America.

 

A map showing the area when the Australian and Pacific tectonic plates collide. Researchers warn a 'megaquake' of magnitude 8 or more could occur in this area.  
Philip Carthew

They cited an earlier paper that said for a magnitude 8.9 Hikurangi subduction quake, losses in the Wellington region alone were estimated to be about $13 billion, with about  3550 deaths and 7000 injuries.

Their findings would allow better modelling of the impacts and help communities prepare to cope with such an event, they said.

The Hikurangi margin, which runs from east of East Cape to offshore of the Marlborough coast, is one of the few subduction zones around the Pacific that has not generated a "great", above magnitude 8, quake in historic times.

 

Data shows that in the southern Hikurangi margin the Australian and Pacific plates are locked and accumulating strain where they meet, about 25km beneath Wellington and Blenheim.

Previous research suggests this locked patch between Cook Strait and Cape Turnagain could generate a quake of between 8.5 and 8.7 magnitude.

In their search for subduction-quake evidence, the researchers used a salt marsh on the edge of Big Lagoon near Blenheim to recover sediment that could be aged by radiocarbon dating.

They collected 48 sediment cores, from 0.5m to 2.2m deep. Analysis and dating of the buried soils in the cores showed there had been two occasions of sudden subsidence of the lagoon in the past 1000 years, indicative of two large quakes.

Jamie Howarth, William Ries and Delia Strong, of GNS Science, using a piston corer to recover sediment cores from salt marsh at Big Lagoon, Blenheim,
to determine the dates of the last megathrust earthquake off the Wairarapa coast.  Kate Clark, GNS Science

The older event was accompanied by a tsunami at least 3.3m high that swept more than 360m inland.

There was no evidence of a tsunami hitting Big Lagoon in the more recent quake, although there were tsunami deposits around Cook Strait, at Abel Tasman and on Kapiti Island about the same time as that event, researchers said.

Lead researcher Dr Kate Clark, of GNS Science, said the findings did not greatly change the actual level of risk to people in central New Zealand.

The National Seismic Hazard Model used a recurrence interval of 550 to 1000 years for a magnitude 8.1-8.4 quake but the researchers had found an actual interval of about 350 years between the two quakes.

While that was different, it was not an irreconcilable difference, given the average was only based on two events. - Stuff.

 

PLANETARY TREMORS: New Zealand Community Told To Prepare For Major Earthquake Along The Dangerous Alpine Fault - Drastic "Fault Avoidance Zone" Recommended!

March 26, 2015 - NEW ZEALAND - A West Coast community will need to consider drastic changes to its town to prepare for an inevitable Alpine Fault earthquake.

The fault runs diagonally through Franz Josef township and geologists have recommended a "fault avoidance zone" 100 metres either side to protect buildings.

GNS Science sent four of its geologists to Franz Josef to talk about what will happen when the Alpine Fault ruptures.

The 600-kilometre fault has ruptured five times in the past 1100 years. Each time it produced an earthquake of magnitude 7.0 to 8.0, the last being in 1717.

Dr Ursula Cochran said studying the fault was complicated because different sections had ruptured at different times.

While researching a section of the fault in South Westland, Cochran and her team found evidence for 24 earthquakes over 8000 years.

Based on this and similar research, scientists calculated the average interval between earthquakes was about 300 years in South Westland.

From that information, scientists conclude there is a 30 per cent chance of a large earthquake occurring on the southern section of the fault in the next 50 years.

That is considered reasonably high by global standards.

Fellow geologist Dr Jamie Howarth said an Alpine Fault earthquake would be accompanied by dramatic changes in the Southern Alps in the following decades.

Scientists had found evidence of an influx of erosion material flowing into lakes and rivers following a large earthquake.

Howarth said that could be seen as a "considerable delayed hazard" with implications for restoration of infrastructure such as road and rail links.

Dr Rob Langridge has worked to map the fault and determine how much it will slip in the next large earthquake.

He said there would likely be instantaneous movement between 7 to 8 metres horizontally and 1 to 2m vertically.

Langridge has worked on the concept of a "fault avoidance zone" which is being considered for the Franz Josef township.

It would mean a 100m-wide zone along the fault, which runs diagonally through the township, with special considerations for buildings.

The Westland District Council has proposed changes to its district plan to account for the earthquake risk in Franz Josef. It will hear public submissions on the changes on March 30 and 31. - Stuff.

MONUMENTAL WEATHER ANOMALIES: The New Breed Of Tremors - Earthquakes In New Zealand Weakened Earth's Crust; Even More Unusual Than First Thought?!

November 26, 2013 - NEW ZEALAND - The Canterbury earthquakes were even more unusual than first thought and unlikely to occur anywhere else in the world, new research reveals.

The research, led by seismologist Martin Reyners of GNS Science, showed the unusual rock structure of the region meant the Canterbury earthquakes produced some of the strongest vertical ground accelerations ever seen in an earthquake.

The makeup of this unique dense and thick slab of rock could have implications for other regions around the lower South Island.

''There will be few other places in the world where a similar earthquake sequence might occur," Reyners said.

The research, published in Nature Geoscience showed that the strong quakes in Canterbury also could cause widespread cracking and weakening of the earth's crust - challenging the common assumption that the strength of the crust was constant.

Normally rocks become hot and ''plastic'' at depths of about 10km. However, the researchers found that strong, brittle rocks continued to a depth of about 30km under Canterbury.

''Strong rocks store and release strain differently to weak rocks," Reyners said.

This unusually thick and dense slab of rock helps to explain the long and energetic aftershock sequence in Canterbury, he said.

Seismic energy would have dissipated more quickly in softer rock.The researchers were now focussed on determining how widespread this strong rock unit is in the lower half of the South Island.

"This is important for defining the earthquake hazard for people living between mid-Canterbury and Southland," Reyners said.

The researchers had initially set out to determine the three-dimensional structure of the crust under Canterbury by using a technique called seismic tomography - similar to a medical CAT scan or ultrasound.

This helps to get more accurate aftershock locations and better define the many smaller faults that ruptured in the earthquakes.

Instead, researchers found that rock properties had changed significantly over a wide area around the Greendale Fault, which ruptured on 4 September 2010 producing a magnitude 7.1 quake.

"This finding was entirely unexpected, but it explains why the main shock released so much energy," Reyners said.

Most of the quakes in the two-year-long Canterbury sequence released abnormally high levels of energy - this was consistent with the ruptures occurring on very strong faults that store energy slowly and gradually and are hard to break.

The Canterbury quakes had their genesis 100 million years ago when very strong rocks became emplaced under Canterbury, he said.

The delay between the September 2010 and Feburary 2011 quakes also may have been caused by a ''strength recovery'' required for the crust following the cracking following the September quake, the research said.The research involved analysing the seismic waves produced by 11,500 aftershocks in Canterbury.

This enabled the team to build a 3D picture of rock structure to a depth of about 35km below the surface.

Reyners said post-quake analysis such as this research was important as it helps to understand how strain builds up in thecrust and how it is released during earthquakes.

"But to do that accurately, we need to understand the types of rocks that exist at depth.''  - Stuff.

PLANETARY TREMORS: Earthquake Flurry Jolts Central New Zealand!

August 02, 2013 - NEW ZEALAND - A flurry of six earthquakes have struck the country overnight, with the strongest, a magnitude 4.9, hitting off Seddon.

USGS earthquake locations.

The 4.9 magntiude quake, which struck just before 1am, was centred 25km south-east of Seddon at a depth of 22km.

It was followed by several smaller aftershocks, the biggest of which was a magnitude 4.5 quake 30km east of Seddon at 6.38am.

GeoNet had reported a magnitude 4.5 quake 15km northwest of Christchurch at 4.12am, but this has since been removed. - Stuff.

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.

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". - USGS.

PLANETARY TREMORS: Indiana Fault System - New Earthquake Fault In New Zealand "Similar To Alpine"!

August 02, 2013 - NEW ZEALAND - An Otago geologist's draft manuscript suggests there's a tectonic fault system off the South Island's east coast potentially comparable in size to the Alpine Fault.

'INDIANIA FAULT SYSTEM': A diagram showing the approximate location of the
proposed Indiania fault in black and red paired lines.

University of Otago geologist Phil Ford has privately written a draft proposal, as yet unpublished, detailing the possibility of the major South Island intra-plate fault, with possible seismic and tsunami hazard implications.

His draft uses previous research that identified beach deposits on the coast east of Milton as potential evidence of tsunami relating to the Akatore fault, or another, hitherto unidentified, offshore system.

Proposing to name it as the Indiania Fault System (IFS), he says it appears to run for most of the offshore length of the South Island, similar in size to the Alpine Fault.

Using New Zealand Institute of Water and Atmospheric Research bathymetric charts, some portions of a fault parallel with the coast were apparent, the paper says.

"It is immediately apparent that portions of the suggested system must be covered by South Island river run-off sediment, at least in places, just as the active and earthquake-related fault in the Christchurch area is covered in gravels and other... sediments onshore."

East of Canterbury and Otago the seafloor feature runs south off southeast Southland and down towards northwest of the Auckland Islands.

"A strike length of greater than 1000km is clear, more than comparable with the Alpine Fault at about 800km south-southwest of the South Island.

"Both the southern IFS elements and southern Alpine Fault offshore continuations are clear and readily visible on seafloor bathymetry displays."

He said the potential of that suggested system warranted immediate research and if shown to be an active fault system then the scale must be "very significant" given a potential overall length of 1600km.

"If the proposed system is accepted by the New Zealand geological fraternity then early notice of serious tsunami vulnerability needs to be passed to governing authorities and civil defence organisations."

GNS Science engineering geologist David Barrell said he was not aware of the proposal but scientists recognised a system of faults off the southeast coast.

The faults, many apparently inactive or remnants of geological activity from the formation of New Zealand, were parallel to the coast and associated with, for example, the Great South Basin or the Waipounamu fault zone.

"It's a fault system that has a history that starts back not long after New Zealand parted company from Australia and Antarctica more than 100 million years ago.

"It's got more of the appearance of a fossil fault rather than anything we would regard as major relating to the present tectonic setting of New Zealand."

Unpublished manuscripts needed peer review and publication in a reputable journal before being accepted as official, he said.

University of Otago geophysicist Dr Andrew Gorman said he would want much more data before making such an assertion and there were other theories.

"I still think the major worry in Otago and Southland is the Alpine Fault itself, and also from the sorts of smaller faults through the South Island." - Stuff.

PLANETARY TREMORS: Major Alert - Officials Tell New Zealand Residents That It's Time To Prepare For An Alpine Fault Earthquake!

July 24, 2013 - NEW ZEALAND - The faultline behind the swarm of quakes in central New Zealand may be much longer than previously realised and therefore capable of larger quakes.

ALPINE FAULT: "An earthquake on the Alpine Fault in the near future would not be a big surprise."

The National Institute of Water and Atmospheric Research is heading into Cook Strait tomorrow to map the area around the swarm of earthquakes that has been rattling Wellington and Marlborough since Friday.

It is hoped the work will identify the faultline from which the quakes have been generated.

GNS Science seismologist John Ristau said that, because the quakes appeared to be happening between the known Vernon and Needles faultlines, it seemed increasingly likely that the London Hill fault was to blame.

In 2003 a Marlborough District Council geotech report described London Hill as a one of "several relatively small faults near the east coast between Seddon and the Waima River".

Dr Ristau said it now appeared the faultline might be much longer than originally thought, which meant it could be capable of creating much larger earthquakes.

"That means it's actually considerably longer than initially thought ... the larger a faultline is, the larger the earthquake."

It was important scientists were able to determine exactly which fault the earthquake had occurred on, as it would allow them to establish whether other nearby faults could now produce large earthquakes as a result.

It appeared the level of stress had not greatly effected the other Wellington faults, but there were a few lines in the Marlborough region that were capable of creating quakes of magnitude 7 or greater.

"If they increase stress, it could trigger a similar-sized earthquake or even a much larger earthquake ... hopefully by the end of the week we'll be able to be a lot more definitive."

Niwa research ship Tangaroa was diverted from survey work in the nearby Pegasus Basin overnight and will spend part of today measuring whether the earthquakes have triggered any landslides in the Cook Strait Canyon.

"We have previously identified an area of potential instability in the middle of the canyon and this will give us the opportunity to see if there have been any changes," marine geologist Scott Nodder said.

An area crossing the earthquake epicentre will also be surveyed to see if the sea floor has changed. Dr Ristau said that mapping would help determine the faultline.

The probability of another big quake, of magnitude 6 or greater, has fallen to 4 per cent within the next day, 13 per cent in the next seven days and 33 per cent in the next year.

The probabilities would continue to fall the longer the region went without a large event, Dr Ristau said.

Aftershocks were likely to continue for about a week.

EARLIER CONCERN OVER IMPACT ON ALPINE FAULT

Yesterday, GNS Science seismologist Stephen Bannister said scientists could not rule out the possibility that the quakes could stir up other faults and "kick off" the Alpine Fault.

He said the biggest misconception the public had when it came to earthquakes was that small ones minimised or took "the edge off" the possibility of a large one occurring.

 However, GNS Science spokesman John Callan said the recent swarm of quakes east of Seddon was "not increasing or decreasing the risk of a quake on the Alpine Fault".

He said the quakes were too far away to affect the Alpine Fault, which stretches 600 kilometres from Milford Sound along the western Southern Alps to Marlborough and is the on-land boundary between the Pacific and Australian tectonic plates.

Recent research led by GNS Science found it last ruptured 296 years ago, and it predicted a 30 per cent chance of a big quake along it in the next 50 years.

The average interval between large quakes on the fault was 330 years.

In the past 8000 years it had ruptured 24 times and caused magnitude-8 quakes, including four in the past millennium. The longest gap between major quakes was 510 years and the shortest 140 years.

"An earthquake on the Alpine Fault in the near future would not be a big surprise. Equally, it could be many decades away, based on its past behaviour," Callan said.

"There is no better time than the present to prepare for the next quake on the Alpine Fault. The more thoroughly we prepare, the lower the eventual impact will be."

He said work was under way to prepare to drill a deep borehole into the fault early next year to study processes taking place at depth inside a major plate boundary fault.

GNS Science is jointly leading the Deep Fault Drilling Project with Otago and Victoria universities, and it involved 22 organisations from eight countries.

An extensive network of seismic instruments, including six "down-hole seismometers" and about 40 surface instruments was recently installed near the planned drilling site so scientists could record the normal level of small quake activity.

The first stage was completed in 2011 with two holes drilled 101 and 105 metres into river terraces next to Gaunt Creek near Whataroa in South Westland.

West Coast tourist town Franz Josef straddled the fault ,but residents were unfazed by quakes in far away regions, such as Wellington, Franz Josef Development Society Incorporated chairman Marcel Fekkes said.

"Everyone is so used to the thing being here, we don't think about it much,'' he said.

"You can't live having fears like that really. When you think about it, the whole country is rather volatile from natural hazards."

Many Franz Josef residents have been fighting Westland District Council plan to establish fault-avoidance zones, which would impose significant restrictions on the township. Submissions closed last September, but a date for public hearings has yet to be set.

EQC BRACED FOR CLAIMS

The Earthquake Commission is bracing itself for an expected flood of claims from property owners throughout the upper South Island and Wellington region.

However, the commission says the quake swarm will not affect the processing of unsettled claims in Canterbury, while Prime Minister John Key says the country can "in principle" afford another earthquake.

EQC has received more than 350 claims after the quakes centred east of Marlborough that shut down central Wellington yesterday and left nerves across the region frayed.

It is already handling 459,198 claims from the Canterbury quakes.

Commission customer services general manager Bruce Emsom said most of the claims were for minor quake damage.

He said there was sufficient cover through levies, reinsurance and the Crown guarantee to provide for all valid claims.

EQC would bring in more field staff, if required, to deal with the influx of claims, so Cantabrians still waiting for their claims to be settled should not be affected.

"There is unlikely to be any impact on processing existing claims from the Canterbury quakes," he said.

Labour's EQC spokesman, Clayton Cosgrove, said that with the commission struggling to keep up with its workload it was important the Government moved swiftly to ensure it had extra resources and personnel so that claims resulting from the Wellington quakes could be dealt with efficiently and without causing any delay to the processing of Canterbury claims.

"You don't want anyone's claim held up," he said.

"Three years into a major catastrophe like this, one would have thought EQC would be well-practised now and have the systems up to deal with this.

''You would hope the mistakes that have been made down here ... would not be replicated and they could expedite claims faster."

Meanwhile, a Christchurch City Council offer to send personnel to Wellington to help authorities assess the extent of the damage has so far not been taken up.

RESEARCH ON SEDDON FAULTS INTENSIFIES

GNS Science seismologist Stephen Bannister said yesterday that intensive research was being carried out to pinpoint where the recent swarm of earthquakes had come from.

It was possible the recent quakes had come from a fault called the London Hill Fault, a relatively small fault near the South Island's east coast between Seddon and the Waimea River, he said.

Scientists would deploy nine extra seismic instruments in coastal Marlborough over the next few days to enable more accurate measurements of the aftershocks.

Seismologists expected to have a clear understanding of the size and geometry of the fault that ruptured on Sunday by the end of the week, along with knowledge of the level of stress change that had occurred on neighbouring faults.

Bannister said the fault the quakes were coming from had the capability to produce magnitude 7s, especially in northern Marlborough, on the Awatere and Clarence faults.

"Yesterday's earthquake may have a flow-on triggering effect to other nearby faults in the vicinity," he said.

"We're quite confident that the earthquakes are not occurring on the major fault between the Pacific and Australian plate, which we call the ‘subduction interface'."

Bannister said aftershocks could reasonably be expected to go on for days. A similar cluster of quakes that occurred just north of Seddon in 1995 had continued for about 11 days.

Probability forecasts for aftershock sequences had been "strongly tested" by the Canterbury sequence, he said.

There was a small possibility that some of the "busy network" of faults in Cook Strait could pose a tsunami threat, prompting a reminder to those near the coast that they should move to higher ground if they felt a strong earthquake shaking the ground for more than 30 seconds, he said. - Stuff.

PLANETARY TREMORS: Rare Earthquakes Rattle Auckland, New Zealand?!

March 17, 2013 - NEW ZEALAND - A "moderate" 3.9 magnitude earthquake that struck Auckland today was the biggest in the city since February 2007, GeoNet says.

The tremor, which struck at 4.05pm, was five kilometres deep and was centred near Motatapu Island, 15 kms north-east of the city.

GeoNet described its intensity as "moderate".

"It's quite rare to get any felt events in Auckland, but occasionally we do have some like this," said duty officer Nico Fournier.

Driveway cracks after the earthquake in Unsworth Heights North Shore.  © Tamaryn Peddie.

He said the earthquake did not indicate an increase in volcanic activity under New Zealand's biggest city, which is dotted with volcanoes.

"Because we have volcanoes in Auckland and then we had this earthquake it doesn't mean the two are related. There is no indication of that."

Further earthquakes were possible, he said.

"Usually when you get earthquakes there are aftershocks, so certainly in the next hours or days there is a possibility of further small earthquakes, but right now it's looking pretty calm.

"There's no indication that it will be the case, but we can't exclude it."

Fire Service spokesman Jaron Phillips said the northern communications centre fielded calls about the quake from across Auckland.

"We've had quite a few calls actually. No actual damage reported, it's really just people after a bit of advice, confirming whether it was an earthquake, a little bit of panic," he said.

"We're just out of the city in Grey Lynn, and it certainly rocked the building here."

Mr Phillips said the earthquake had triggered an alarm at a rest home in Howick, but no damage was reported.

He urged people not to clog up emergency lines if they did not need to, but they could call if they had damage to report or needed assistance.

Many people in central Auckland felt the quake.

Blues captain Ali Williams tweeted "That was an earthquake. Yes in Auckland" and Comedian Rhys Darby tweeted "Yip, just felt an earthquake in AKL".

Around five minutes earlier GeoNet detected another quake, measuring 3.3. It was centred 25 kms north-east of Auckland at a depth of 23 kilometres.

Many Aucklanders said they barley felt the first earthquake, but the second quake was much stronger.

Readers who emailed the Herald described it as being like a large truck going past, a gust of wind or a truck colliding with the house.

Bev Hooper of Stanmore Bay said she though the first quake was "a bit odd" but the second quake came as a bigger jolt.

"It felt like a truck had hit the side of the house. Just a hard jolt."

Paremoremo resident Catherine Casey said she and her husband heard a "massive rumble" about 4.05pm.

"My husband thought it was a gust of wind but we had no wind. I said I think it was an earthquake ... I am deaf in one ear but it was loud and I felt the vibration. I thought it was a tornado."

A resident of Rothesay Bay on the North Shore said the second quake lasted from 30 seconds to a minute.

The walls of her lounge moved, shifting a painting, and the cups in front of her rattled loudly.

The earthquake was a first for Glenfield resident Maree Lawson, who has lived on the North Shore her whole life.

"Never experienced anything like that. I was watching a DVD on my bed, then the bed starts shaking like someone was underneath it ... very freaky."

Sunnynook resident Val said the quakes felt like "a very strong gust of wind shaking the house". The floor moved rapidly for a few seconds and the cat fled as the house shuddered.

A Torbay resident said her whole room started shaking during the first quake.

"I thought someone just crashed into the house! It lasted for 10 seconds and when I looked outside everything was fine ... About four minutes later, my whole house started shaking and I heard my siblings scream and I ran to their aid."

Kim said she thought she'd had "one wine too many" until her neighbour confirmed her shock that there had been an earthquake.

"I believed my neighbour before I believed my husband. My chair shook and my glasses rattled. My neighbour's whole house shook along with his blinds."

The tremors have encouraged some Aucklanders to stock up on Civil Defence emergency supplies.

Glendowie woman Caroline Wood, who saw the walls of her house shake, said she would take the quake as a warning to be prepared.

That sentiment was echoed by Lisa West in Birkenhead, who felt a jolt and the kitchen rattled.

"Quite frankly it freaked me out, enough to shake me out of apathy with regard to sorting out a household plan for a civil defence emergency. I'm getting onto it first thing Monday!"

The earthquake has already prompted a Facebook page called "I survived the Auckland Earthquake", where users are sharing humorous memes.

Within an hour of the quakes the page had more than 2000 likes on Facebook.

Auckland Civil Defence said small earthquakes are not unusual for Auckland. A similar swarm occurred over an evening in February 2007.

People who felt the earthquake are being urged to register it on GeoNet's website by clicking the 'Felt it?' button. - NZ Herald.

PLANETARY TREMORS: The Alpine Fault - Geologists Says Mega-Earthquake In New Zealand Could "Melt Rocks"; Fault Line Could Get As Hot As 1,000 Degrees!

March 17, 2013 - NEW ZEALAND - The next time the Alpine Fault "goes", it is likely to be a big one, but the earthquake on the surface will be a tiny fraction of the power unleashed beneath.

University of Canterbury researcher Carolyn Boulton is finishing her research on the plate boundary that splinters the South Island and what happens underground when it ruptures.

ALPINE FAULT: An 800 kilometre-long fault which runs along the western
edge of the Southern Alps from Marlborough to Milford Sound.

The energy that went into surface shaking was less than 5 per cent of the energy released by the fault rupturing, she said.

"A lot of it is just used up on the fault itself,'' she said.

"Most of [it] is used up as heat on the fault and it's also used up to crush and pulverise [rocks]. The remainder, whatever is left, that's what's sent out as seismic waves."

Dry parts of the fault line can get so hot - about 1000 degrees Celsius - that the rock melts.

The "main divide" of the Alpine Fault is that dry only at great depths, but branches at its northern end - the Hope, Clarence, Wairau and Awatere faults - also have little water.

Boulton recreated Alpine Fault conditions at three university laboratories in the United States and China for her research and built an instrument to simulate quake shaking here.

"We have a machine [in Christchurch] that we put the rocks into and we simulate earthquake conditions,'' she said.

"We have learnt that the fault gets stronger with increasing temperature and pressure with increasing depth [and] that when an earthquake occurs, the Alpine Fault's strength dramatically decreases."

The Alpine Fault's last major quake was in 1717 and had a magnitude between 7.9 and 8.1.

GNS Science estimates there is a 30 per cent probability of the next quake on the fault occurring in the next 50 years. - Stuff.

DISASTER IMPACT: Poverty "Rampant" In Quake Hit Christchurch - High Levels Of Stress And Mental Health Issues!

January 31, 2013 - NEW ZEALAND - Horror stories of Christchurch families living in garages and tents continue to surface almost two years on from the February 2011 earthquake.  Some families are still stranded in sheds or illegally overcrowding friends' and relatives' houses.  Meanwhile, rental housing prices show no sign of abating and welfare agencies believe this year could be worse than the last.  Demand on Christchurch's social services continues to increase: people who have never needed help before are queuing up at food banks and many families still face impoverished living conditions. 

The housing crisis in Christchurch has left
mother-of-two Amber Breiter with no choice
but to live in a single garage - Source: Fairfax.

Poverty "Rampant" In Quake Hit Christchurch.

City Missioner Michael Gorman said the unprecedented demand on the mission's alcohol and drug services, foodbank and night shelters "has not eased at all".  "There is a lot more money going into rent and a lot less money going into living."  The number of people approaching the mission suffering from poverty or mental health issues was rampant, he said.  One of his social workers had a week-long waiting list of families needing assistance with school uniform grants. Another had recently been supporting a young family living in a tent, and a couple renting a washhouse.  A desperate woman with a newborn baby emailed Gorman last week asking for any free food because she said she was "paying so much rent, I can't afford to live".

"We are seeing many, many new people. Some who may actually own property but are so stretched by having to be out of their houses and pay horrific rents," he said.  Pacific Island Evaluation social worker To'alepai Louella Thomsen-Inder said she was growing tired of "fighting day and night" for her clients.  Before Christmas she dropped food parcels off to 10 struggling families and said she could "smell the poverty as I walked in the door".  "I saw the reality. Some people had just a twig in a corner for a Christmas tree," she said.  "Some homes have no curtains, babies are crawling around on rotting carpet, it's damp and the children are running around with no shoes on and with visible skin conditions."  Tenants Protection Association manager Helen Gatonyi believes this year is "shaping up to be the worst".  "When winter strikes this year, we predict it's going to be very difficult for a large number of people."  Some owners had been renting out cramped, damp three-bedroom homes for more than $500 a week, she said.  "The behaviour of some landlords is totally unacceptable. They are renting homes for an arm and a leg, knowing there will be a queue of people lining up to view the place."  Gatonyi is calling for a warrant of fitness and code of practice to be placed on Christchurch rental properties and said the association was about to launch an in-depth inquiry into the living conditions of tenants in the city.  The Government's investigation into overcrowding, homelessness and unsuitable living conditions in Christchurch was kick-started in June last year, but the results are yet to be released.  The Ministry of Business, Innovation and Employment had hoped to have the report finalised by the end of last year.  A spokeswoman said the release had been pushed back to ensure the information was correct and the report "robust".  According to recent ministry figures, rents rose between 7 and 21 per cent in Christchurch last year, depending on suburb. - TVNZ.

Researcher Ellen Sole is investigating earthquake
stress levels in Christchurch children. Photo / Supplied.

Study: Quake Kids Still Stressed.

Christchurch children are still suffering from anxiety two years after the earthquakes, a new study concludes.  Now, researchers at the University of Canterbury are looking at how vitamins and minerals can help treat psychological and psychiatric symptoms, including stress, mood and ADHD.  It's believed to be the first study in the world looking at micronutrients and anxiety in children.  While some children remain anxious or worried about earthquakes in particular, for others the events triggered worries about other things, says researcher Ellen Sole.  "The issue for a number of children experiencing anxiety is that the range of symptoms of anxiety can widely interfere with their development. This includes affecting friendships, school performance and a child's happiness," she said.  "Many anxious children will have difficulties sleeping. Combining this with worries and the other difficulties anxiety can have puts a large strain on the family, sometimes negatively affecting family life."

 Common symptoms of anxiety in children include sweating, feelings of choking or dizziness, shortness of breath, heart palpitations, being easily startled, restlessness, difficulty concentrating, headaches, stomach aches, body aches and tiredness as well as behavioural symptoms including clinginess, tantrums, withdrawing from friends and family, avoidance of places or objects, not wanting to go to school, shyness and perfectionism.  Ms Sole is appealing for "a small number" of children who would be willing to try the vitamins and minerals for approximately two months.  "Certainly Christchurch children have had to cope with much more than a lot of children do, so we would expect that some of these children will struggle," she said. - NZ Herald.