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: Global Seismic Uptick - Powerful 7.2 Magnitude Earthquake Strikes Off Raoul Island, New Zealand; No Tsunami Warning; 6.3 & 6.2 Magnitude Aftershocks! [MAPS+TECTONIC SUMMARY]

June 23, 2014 - NEW ZEALAND - A powerful earthquake measuring 7.2 on the Richter scale jolted 126 km southeast of Raoul Island, New Zealand at 19:19:16 UTC on Monday, the U.S. Geological Survey said.

USGS earthquake location.

The epicentre, with a depth of 5 km or 3.1 miles, was initially determined to be at 30.100 degrees south latitude and 177.000 degrees east longitude.

The Pacific Tsunami Warning Center said no destructive widespread tsunami threat existed, based on historical earthquake and tsunami data.

USGS earthquake shakemap intensity for the 7.2 magnitude earthquake.

USGS has subsequently downgraded the initial recording of the earthquake from 7.2 to 6.9. Two strong aftershocks were also registered, a 6.3 and a 6.2.

USGS earthquake shakemap intensity for the 6.3 magnitude aftershock.

Raoul Island is the northernmost inhabited outpost of New Zealand and is permanently manned. The island is no stranger to large quakes, a magnitude 7.6 hit in July 2011 and generated a small tsunami. A 7.4 hit later that same year in October.

New Zealand sits at the southwestern edge of the Pacific "ring of fire," an area of high seismic and volcanic activity that stretches up through Japan, across to Alaska and down the west coasts of North and South America.

In February 2011, a 6.3-magnitude earthquake toppled buildings in the South Island city of Christchurch, killing 185 people and injuring several thousand.

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 6.1 Magnitude Earthquake Strikes Off Raoul Island, New Zealand!

August 28, 2013 - NEW ZEALAND - An earthquake measuring 6.1 on the Richter scale jolted 288 km northwest of Raoul Island, New Zealand at 0254 GMT Wednesday, the U.S. Geological Survey said.

USGS earthquake location.

The epicentre, with a depth of 488.61 km, was initially determined to be at 27.7953 degrees south latitude and 179.6722 degrees east longitude.

The Pacific Tsunami Warning Center and New Zealand authorities both said there was no tsunami threat.

The quake was at a distance of 902km (560miles) southwest of Nuku`alofa, Tonga; 1014km (630miles) northeast of Whangarei, New Zealand;  1076km (669miles) south of Suva, Fiji; and 1100km (684miles) northeast of North Shore, New Zealand.

USGS earthquake shakemap intensity.

New Zealand sits at the southwestern edge of the Pacific "ring of fire," an area of high seismic and volcanic activity that stretches up through Japan, across to Alaska and down the west coasts of North and South America.

In February 2011, a 6.3-magnitude earthquake toppled buildings in the South Island city of Christchurch, killing 185 people and injuring several thousand.

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 6.2 Magnitude Earthquake Strikes Kermadec Islands Region - Northwest Of Raoul Island, New Zealand!

April 26, 2013 - NEW ZEALAND - A strong 6.2 magnitude earthquake has hit the Kermadec Islands region, 115 kilometres of Raoul Island, New Zealand on April 26 at 06:53:28 UTC.

The quake hit at an estimated 349 kilometres (216.9 miles) deep, according to the US Geological Survey.

There were no immediate reports of damage or injuries caused by the quake.

Google Earth earthquake location.

The Pacific Tsunami Warning Center did not issue a tsunami alert.

Earthquakes are common in New Zealand, which is part of the geologically active part of the Pacific Ring of Fire.

The most recent powerful quake in the country happened in December 2011 near Christchurch, causing huge damage in the region, with a magnitude of 6.0.

This followed just 10-months after another quake which devastated the city and killed 185 people.

USGS earthquake shakemap intensity.

Meanwhile, residents have reported being mildly shaken by an earthquake near Wairoa in the Hawkes Bay tonight.

The magnitude 4.4 quake, centered 20km northwest of the town, hit just before 7pm, GeoNet reported.

It had a depth of 5km.

Five residents in the area reported feeling slight or weak shaking, said the website. - NZ Herald.

Tectonic Summary - Seismotectonics of the Eastern Margin of the Australia Plate.

The eastern margin of the Australia plate is one of the most sesimically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand.

Since 1900 there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

North of New Zealand, the Australia-Pacific boundary stretches east of Tonga and Fiji to 250 km south of Samoa. For 2,200 km the trench is approximately linear, and includes two segments where old (greater than 120 Myr) Pacific oceanic lithosphere rapidly subducts westward (Kermadec and Tonga). At the northern end of the Tonga trench, the boundary curves sharply westward and changes along a 700 km-long segment from trench-normal subduction, to oblique subduction, to a left lateral transform-like structure.

USGS earthquake location.

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.

USGS earthquake details.

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: 6.2 Magnitude Earthquake Strikes Remote Pacific Area - Seismic Swarm Developing Along the Kermadec Islands, New Zealand!

A strong 6.2-magnitdue earthquake struck beneath the Pacific off New Zealand's Kermadec Islands on Sunday, US geologists said, but no tsunami warning was issued.

The remote offshore quake hit at 01:42 am (1742 GMT) at a depth of 28 kilometres (17 miles), 44 kilometres east southeast of Raoul Island and 937 kilometres south southwest of Tonga, the United States Geographical Survey said.

The Pacific Tsunami Warning Center did not issue a tsunami alert for the area, part of the Pacific's "Ring of Fire", a highly active tectonic zone that frequently experiences earthquakes.

The initial quake was followed five minutes later by a 5.2-magnitude aftershock in a similar area.

The remote Kermadec Islands are New Zealand's northern most islands, 1,100 kilometres north of Auckland. - Yahoo Australia.

The earthquake was later downgraded by the USGS to a 5.8 magnitude. There appears to be a seismic swarm developing in the area, as the first tremor was later followed by 5 other earthquakes of 5.0 magnitude or above.

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: 7.6 Quake Rocks Kermadec Islands Region!

Map of the 7.6 magnitude earthquake in the Kermadec Islands Region.

A magnitude 7.6 earthquake has struck the Kermadec Islands Region at a depth of 39.8 km (24.7 miles). The quake hit on Friday, October 21, 2011 at 17:57:17 UTC and was located at 28.941°S, 176.046°W.

The epicentre was 180 km (112 miles) east (79°) from Raoul Island, Kermadec Islands; 870 km (541 miles) south (185°) from Nuku'Alofa, Tonga; and  2978 km (1851 miles) southwest (240°) from Papeete, Tahiti, French Polynesia.

According to NOAA's National Weather Service, there is no watch, warning or advisory in effect at the moment.

A strong earthquake struck far off the South Pacific island nation of Tonga on Friday, but there were no immediate reports of damage or injuries. The U.S. Geological Survey reports the magnitude-7.6 quake struck Friday at 1:57 p.m. (1757 GMT) about 541 miles (870 kilometers) south of Nuku'Alofa on Tonga. The quake struck at a depth of 24 miles (39 kilometers). The Pacific Tsunami Warning Center did not issue a tsunami alert, but its report on the quake said sea level readings indicated that a tsunami was generated. The quake hit 112 miles (180 kilometers) from New Zealand's remote, volcanic Kermadec Islands. The remote outpost is generally uninhabited aside from a weather station and a hostel for visiting New Zealand scientists and staff. The New Zealand Herald newspaper reported the country's National Crisis Management Center had been activated, and that Civil Defense officials warned people in coastal areas to stay off beaches. Another magnitude-7.6 earthquake struck the region in July, but the eight New Zealand staffers at the Raoul Island outpost at the northern end of the Kermadecs were unharmed. The region lies on the "Ring of Fire" — an arc of earthquake and volcanic zones that stretches around the Pacific Rim. About 90 percent of the world's quakes occur in the region. - Associated Press.

Stay tuned.

PLANETARY TREMORS: 6.1 Quake Hits South of Kermadec Islands!

Map of the earthquake's epicentre.

A magnitude 6.1 earthquake has struck South of the Kermadec Islands at a depth of 34.6 km (21.5 miles). The quake hit at 08:58:29 UTC Friday 7th October 2011 and was located at 32.389°S, 178.902°W. The earthquake was originally listed by U.S. Geological Service (USGS) as a magnitude 6.5.

Kermadec Islands earthquake seismicity.

The epicentre was 106 km ( 65 miles) south of L'Esperance Rock, Kermadec Islands; 359 km (223 miles) southwest of Raoul Island, Kermadec Islands; 762 km (473 miles) northeast of Auckland, New Zealand; and 1136 km (705 miles) northeast of Wellington, New Zealand.

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

This is the second magnitude 6.0 or over earthquake since the start of October, following the 6.2 tremor that struck Jujuy in Argentina yesterday.

Planetary Tremors: Seismic Swarm at Kermedec Islands Region!

A magnitude 5.8 earthquake has struck the Kermadec Islands Region at a depth of 23.3 km ( 14.5 miles). The quake hit at 15:02:29 UTC Saturday 9th July 2011. The epicenter was 79 km (49 miles) east of Raoul Island, Kermadec Islands. No tsunami watch, warning or advisory is in effect. There are no reports of any damage as yet.

Planetary Tremors: 5.3 Magnitude Quake hits Kermadec Islands!

A magnitude 5.3 earthquake has struck the Kermadec Islands Region at a depth of 20.4 km ( 12.7 miles). The quake hit at 12:54:22 UTC Saturday 9th July 2011. The epicenter was 156 km (96 miles) east of Raoul Island, Kermadec Islands. No tsunami watch, warning or advisory is in effect. There are no reports of any damage as yet.

PLANETARY TREMORS: 6.0 Quake in Kermadec Islands Region?!

A magnitude 6.0 earthquake has struck Kermadec Islands Region at a depth of 19.9 km ( 12.4 miles). The quake hit at 09:10:52 UTC Thursday 7th July 2011. The epicenter was 119 km (73 miles) east of Raoul Island, Kermadec Islands. No tsunami watch, warning or advisory is in effect. There are no reports of any damage as yet.

PLANETARY TREMORS: 7.8 Quake Hits Kermadec Islands Region!

A tsunami alert has been issued, following a magnitude 7.8 earthquake, that struck the Kermadec Islands Region at a depth of just 1 km ( - .0 .6miles). The quake hit at 07:03:15 UTC Wednesday 6th July 2011. The epicenter was 163 km (101 miles) east of Raoul Island, Kermadec Islands. There are currently no reports of any damage as yet.

The tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) and is in effect for the Kermadec Islands, Tonga and New Zealand. The bulletin applies to areas within and bordering the Pacific Ocean and adjacent seas, except for Alaska, British Columbia, and the states of Washington, Oregon and California.