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: Powerful 6.5 Magnitude Earthquake Strikes Southeast Of L'Esperance Rock, New Zealand!

February 02, 2014 - NEW ZEALAND - A strong earthquake struck off the uninhabited Kermadec Islands in the South Pacific Ocean on late Sunday evening, seismologists said, but no tsunami warnings were issued. Damage or casualties in the New Zealand-governed region were not expected.

USGS earthquake location.

The 6.4-magnitude earthquake at 10:26 p.m. local time (0926 GMT) was centered about 188 kilometers (116 miles) southeast of L'Esperance Rock, which is located halfway between New Zealand's North Island and Tonga. It struck about 33 kilometers (20.5 miles) deep, making it a shallow earthquake, according to New Zealand's seismological agency GeoNet.

The United States Geological Survey (USGS) put the magnitude of Sunday's earthquake at a stronger 6.5, but determined the depth to be slightly deeper at 40.4 kilometers (25.1 miles). It said it was unlikely to have been felt on Raoul Island, which is home to a government-run station.

Both the New Zealand government and the Joint Australian Tsunami Warning Center determined there was no tsunami threat to their coastlines. The Pacific Tsunami Warning Center also said there was no threat of a destructive widespread tsunami, although it initially cautioned about a very small risk of local tsunamis.

USGS earthquake shakemap location.

New Zealand's Kermadec Islands and the surrounding region as a whole are part of the so-called 'Pacific Ring of Fire,' an arc of fault lines circling the Pacific Basin that is prone to frequent and large earthquakes. Volcanic eruptions also occur frequently in the region.

In October 2011, a powerful 7.4-magnitude earthquake struck about 169 kilometers (105 miles) east of Raoul Island, generating a small tsunami but causing no damage. The largest tsunami wave, approximately 0.17 meter (0.6 feet) above normal sea levels, was recorded at Fishing Rock on Raoul Island.

Three months earlier, in July 2011, a 7.6-magnitude earthquake struck about 163 kilometers (101 miles) east of Raoul Island. The powerful earthquake generated a 1-meter (3.2 feet) tsunami that hit the island, but no damage or casualties were reported. - Wire Update.

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.

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". - USGS.

PLANETARY TREMORS: Powerful 6.3 Magnitude Earthquake Strikes Northeast Of L'Esperance Rock, New Zealand!

October 11, 2013 - NEW ZEALAND - A 6.3 magnitude earthquake struck New Zealand today. But the quake was far out to sea.

USGS earthquake location.

Officials tell news that a 6.3 magnitude New Zealand earthquake today began just after 9:24 am local time. The quake however had a huge depth. USGS indicates to news that the quake started ninety-one miles below sea level.

Reps tell news however that the quake was out to sea northeast of L’Esperance Rock. The quake was roughly fifty-four miles northeast of L’Esperance. It was also roughly six hundred miles from Whaktane, and Tauranga. Reps also tell news that the quake was roughly seven hundred miles from Tonga.

USGS earthquake shakemap intensity.

And while L’Esperance Rock has generated several significant quakes this year, the damaging quakes have been near Wellington. For example, in July a 5.3 magnitude quake struck that region. That quake was twenty-seven miles southwest of Karori as well. The quake was also was twenty-nine miles southwest of Wellington and thirty-seven miles south of Lower Hutt. The quake also started thirty-nine miles south of Porirua.

In July 2012, a 6.2 New Zealand earthquake struck thirty-five miles southwest of Opunake. That quake was thirty-nine miles southwest of Hawera and sixty-four miles southwest of New Plymouth. The quake also erupted seventy-one miles west of Wanganui. - Lalate.

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.

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". - USGS.

PLANETARY TREMORS: Powerful 6.7 Magnitude Earthquake Strikes Northeast Of L'Esperance Rock, New Zealand!

September 30, 2013 - NEW ZEALAND - A powerful 6.7-magnitude earthquake struck near the Kermadec islands this morning.

The tremor was located at 81km northeast of L'Esperance Rock, New Zealand, with epicenter initially determined to be at 30.923 degrees south latitude and 177.631 degrees west longtitude.

USGS earthquake location.

USGS earthquake location.

New Zealand's National Crisis Management Centre was activated after the quake struck at 05:55:54 UTC today, at a depth of 34.8km (21.6miles).

The Pacific Tsunami Warning Centre (PTWC) issued a Tsunami Information Bulletin in response to the earthquake, stating that no destructive widespread tsunami threat exists.

The PTWC bulletin was based on historical earthquake and tsunami data, and did however indicate that local tsunamis could be generated that can be destructive along coasts located within a hundred kilometers of the quake's epicenter.

L'Esperance Rock, formerly French Rock, is the southernmost islet in the Kermadec Islands, to the north of New Zealand.

USGS earthquake shakemap intensity.

New Zealand, lies on the so-called Pacific “Ring of Fire,” where continental plates collide causing frequent seismic activity.

Today's quake constitutes the fourth 6.7 or higher magnitude felt across the planet, over the last six days.

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.

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". - USGS.

PLANETARY TREMORS: Strong 5.6 Magnitude Earthquake Strikes Southeast Of L'Esperance Rock, New Zealand!

September 21, 2013 - NEW ZEALAND - An earthquake measuring 5.6 on the Richter scale jolted 242km south of L'Esperance Rock, New Zealand at 00:48:59 Hong Kong Time on Sunday (16:48:59 GMT on Saturday), the U.S. Geological Survey said.

USGS earthquake location.

The epicentre, with a depth of 10.0 km, was initially determined to be at 33.512 degrees south latitude and 178.0872 degrees west longitude.

USGS earthquake shakemap intensity.

New Zealand is part of the so-called Pacific "Ring of Fire" that receives regular seismic activity. A severe earthquake in the city of Christchurch in 2011 killed 185 people and destroyed much of the city's downtown. That earthquake had a magnitude of 6.3; however, the epicenter was located just 6 miles southeast of the city.

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.

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". - USGS.

PLANETARY TREMORS: Magnitude 6.3 Earthquake Jolts South of the Kermadec Islands!

An earthquake measuring 6.3 on the Richter scale jolted south of the Kermadec Islands at 1010 GMT on Thursday, the U.S. Geological Survey (USGS) said.

The epicentre, with a depth of 34.10 km, was initially determined to be at 32.6037 degrees south latitude and 179.1035 degrees west longitude.

The epicenter was 130 km (80 miles) south of L'Esperance Rock, Kermadec Islands; 386 km (239 miles) southwest of Raoul Island, Kermadec Islands; 734 km (456 miles) northeast of Auckland, New Zealand; and 1107 km (687 miles) northeast of Wellington, New Zealand. The epicentre was just 456 Miles from Auckland, New Zealand and follows a tremor of 5.6 magnitude earlier this morning that hit the same area, with an epicentre of 721 miles from Auckland.

No tsunami warning was issued and there are currently no reports of any injuries or damage at this time.

Planetary Tremors: Double 5 Magnitude Quakes - Kermadec Islands!

Two 5 magnitude earthquakes struck the south of the Kermadec Islands. The first one, a magnitude 5.5, hit a at a depth of 9.8 km (6.1 miles). The quake hit at 10:51:33 UTC, Tuesday 6th September 2011 and was located at 34.096°S, 179.469°E. The epicentre was 525 km (326 miles) northeast from Auckland, New Zealand; 332 km (206 miles) southwest of L'Esperance Rock, Kermadec Islands; 523 km (324 miles) northeast of Gisborne, New Zealand; and 899 km (558 miles) northeast of Wellington, New Zealand. The second, 5.1 magnitude, also struck south of the Kermadec Islands at a depth of just 1 km (0 miles). The quake hit at 13:10:17 UTC, Tuesday 6th September 2011 and was located at 34.018°S, 179.504°E. The epicentre was 513 km (318 miles) northeast from Auckland, New Zealand; 341 km (211 miles) southwest of L'Esperance Rock, Kermadec Islands; 517 km (321 miles) northeast of Gisborne, New Zealand; and 890 km (553 miles) northeast of Wellington, New Zealand.

No tsunami warning was issued and there are no reports of any damage at this time.