The Christchurch Earthquake, which killed 185 people on February 22, 2011, was New Zealand's most devastating in recent history. Photo / NZ Herald
Two hundred and twenty six thousand, four hundred and twenty seven.
That's how many quakes greater than magnitude 4.0 - typically big enough to be felt - have registered on GeoNet sensors since January 1, 2010.
There were 53 between 6.0 and 6.9 - among them the devastating Christchurch Earthquake, and the twin events that hit Marlborough in 2013.
Another half a dozen were over 7.0.
The three biggest, by magnitude, were 2016's mountain-moving Kaikoura Earthquake, at 7.8; the 7.1 Te Araroa quake that struck the East Cape just a few weeks earlier; and the 7.1 Darfield event of September 2010, kick-starting a years-long aftershock sequence in Canterbury.
Amid the disruption and devastation these disasters caused, scientists have learned much more about the complex geological puzzle that is our seismic environment.
The Herald looks back at five of the biggest jolts.
Darfield was the quake that started it all: thousands of aftershocks, the ensuing tragedy at Christchurch, billions of dollars in damage, and a nationwide effort to make all buildings quake-safe.
When the 7.1 quake struck amid early morning darkness at 4.35am on Saturday, September 4, 2010, lightning could be seen streaming not from the sky, but from the ground.
Amid the 40-second rumble, the ground acceleration created by the thrusting caused stress-induced electrical currents deep within the Earth's crust to rise rapidly and fire from the surface.
GNS Science seismologists were quickly able to identify the quake's cause as strike-slip faulting, where two blocks of the crust violently tear past each other, near the eastern foothills of the Southern Alps, at the western edge of the Canterbury Plains.
They described the event as an "extremely rare seismic recording near a fault rupture".
People in Christchurch, 40km east, likened it to a train, a hurricane, and a battle tank rolling down the street.
More than 6000 people reported feeling it.
At Christchurch Airport, chaos descended as the lights were knocked out; at Kaiapoi motorcamp, caravans sank to their axles as craters opened; shaken revellers stepped out of city bars into blackness and debris.
In those 40 seconds, billions of dollars of damage resulted as sewer lines were broken, roads opened up, chimneys collapsed and residents of low-lying communities like Bexley were introduced to the slushy nightmare of soil liquefaction.
By comparison, the level of shaking approximately coincided with the strength of a one-in-500- year quake event that our building code is now tested against, and its force released about 30 times more energy than the July 2013 Cook Strait earthquake.
GNS Science seismologist John Ristau said at least six faults were involved in the Darfield earthquake.
"Another interesting aspect of the Darfield earthquake was it triggering significant aftershocks well outside of what we would normally consider an aftershock zone - in this case the earthquakes in Christchurch and Pegasus Bay," he said.
The length of the Canterbury sequence had also been interesting, with major aftershocks – like the Valentine's Day, 2016, 5.8 event in Pegasus Bay – coming years later.
Darfield proved to be the most damaging quake in New Zealand since the deadly magnitude 7.8 Hawke's Bay earthquake in 1931 – a record quickly overshadowed by chaos wreaked in Christchurch six months later.
At 12.51pm on February 22, 2011, workers in Christchurch's busy CBD were finishing up lunch-breaks when a quake, just 5km deep and 10km east of the city centre, erupted with the force of 10,000 tonnes of TNT.
Its violent force was so great it was considered statistically unlikely to happen more than once in a millennium - and far exceeded the loading extremes that New Zealand buildings were designed for.
A massive cloud of dust enveloped the city as 100,000 homes were damaged - largely in the eastern suburbs – as were more than half the buildings in downtown Christchurch.
One of those was the CTV Building at the corner of Cashel and Madras Sts; 115 people perished when it collapsed, with just a north shear wall still left standing amid the rubble.
Eighteen more died when the five-storey Pyne Gould Building collapsed and eight people were crushed when masonry fell on Red Bus number 702 in Colombo St.
Elsewhere in the city centre, 28 people were killed; another 12 died Christchurch's suburbs.
Christchurch Hospital alone treated between 6600 and 6800 people, as the city – nearly 80 per cent of it without power – became one enormous emergency scene.
The quake was triggered by a rupture of a 15km-long fault along the southern edge of the city, running from Cashmere to the Avon-Heathcote estuary, but was still considered an aftershock of the September 4 event.
Canterbury was known to be home to around 100 faults, and, until then, the closest to the city thought to be capable of triggering major quakes was found in the Rangiora-Cust area.
Amid the slow, multi-billion-dollar rebuild that still continues, Christchurch residents banded together in solidarity, forging what psychologists termed "identity fusion".
And the earthquakes continued: more than 15,600 were recorded as part of the sequence, including another sizeable 6.0 quake in the city in June that year.
It was the year of the "doublet" – a pair of quakes in the Cook Strait area that shook Marlborough and rattled the capital.
The first, magnitude 6.5 event - named the Seddon earthquake after the Marlborough town near where it struck just after 5pm on Sunday, July 21, 2013 - was strong enough to blow out windows, crack concrete, cause buildings to sway and send people running for cover on both sides of the strait.
In Wellington, where 35 buildings were damaged, glass fell on to Lambton Quay and Featherston and Willis St; in Seddon, the local rugby club was turned into a welfare centre amid black-outs throughout the town.
Local woman Joan Dodson was forced to spend the night in her 4WD after part of the ceiling of her and husband Rex's home collapsed.
Just as insurers were working through some 1000 claims, a second big quake hit at nearby Lake Grassmere, just after 2.30pm on Friday, August 16, 2013.
That 6.5 shake proved big enough to shift Cape Campbell 18cm to the west and caused minor damage to buildings in Wellington, where workers took off home early.
Again, Seddon suffered the worst impacts, with five houses damaged so badly that they are uninhabitable.
One of them, an 1874 heritage cottage made of cob, was shifted backward and forward in the quake, to the point its owner described it as being "cracked all the way through like a pavlova".
Scientists identified it to be a "strike-slip earthquake'', where each side slides past the other without uplift and down-thrust, and the same kind of quake that preceded it.
After the events, scientists pointed to a complex network of faults on the Cook Strait seabed – one likening the busy seismic environment to "grand central station".
The fault zone had a history of producing swarms of quakes, but none that had been devastating in the hundreds of years since records began.
In all, more than 3800 aftershocks were linked to the unusual doublet.
The 7.1 quake that rocked the North Island's East Cape early on September 2, 2016, was perhaps more memorable for the chaos that followed it.
Soon after the 4.37am jolt – centred 125km northeast of Te Araroa, at a depth of 22km – tens of thousands of people across the North Island were left worried over the possibility of a tsunami.
Yet a potential tsunami threat notice wasn't issued until 5.33am - and a request for an emergency announcement to be broadcast wasn't made until 5.58am.
Met with fierce criticism over the episode, Civil Defence responded by reviewing its processes.
In any event, any recognisable tsunami never came: waves measuring just 30cm in height were recorded by tide gauges at East Cape and Great Barrier Island.
There were no reports of injuries, but house walls were cracked and there was damage to private water supplies in Gisborne.
Power was also cut to about 1000 homes in Eastern Bay of Plenty and several schools in the region were closed.
The quake, the biggest to hit the area in 20 years, was followed the next month by a 5.8 aftershock that was felt by about 400 people from around the North Island and upper South Island.
The offshore area where the quakes hit – where the Pacific Plate subducted beneath the Australian Plate – was considered one of the most seismically active regions in the country.
"More than 3100 earthquakes were located as part of this sequence - however, due to the offshore location there were likely many smaller aftershocks that could not be located," Ristau said.
It was one of the most complex quakes ever recorded anywhere on the planet: a monster that moved mountains and erupted with the equivalent energy release of 400 atomic bombs.
More than 20 faults were activated by the 7.8 Kaikoura Earthquake that struck just after midnight on November 14, 2016 – around a dozen of them rupturing violently enough to displace land by more than a metre.
Nowhere was this more dramatic than along Marlborough's Kekerengu Fault, where the land was offset by as much as 12m.
In some places the fault was visible with raised-up folds of earth stretching across the countryside – and along the Kaikoura coastline, the seabed, and marine life upon it, was hauled from the ocean.
Beginning just north-east of Culverden, the sequence lasted for about two minutes, sending seismic waves from Canterbury and up into the North Island, which moved west by about 5cm.
Two people died – one in the collapse of the historic Elms Farm homestead, near Kaikoura, and another in a damaged log house at Mt Lyford.
A tsunami reaching 7m hit Goose Bay; 100,000 landslides came down around the South Island, and many roads and sections of highways were left blocked, cutting off Kaikoura for weeks.
Wellington was rattled again, and several buildings – including the former ICI Building in Molesworth St and the Reading Cinema parking building – had to be demolished after sustaining damage.
In all, insurance claims totalling more than $1.8b were lodged.
As a seismologist, Ristau was still awed by the event's sheer complexity – and the dramatic natural effects it caused.
"It gave a perfect example of how major earthquakes cannot be considered as a simple rupture on a fault, but instead are a series of faults that rupture in rapid succession."
Kaikoura also showed that fault ruptures could stepover – or jump between faults - across much longer distances than previously thought.
"Stepovers of more than 20km were mapped which had never been observed anywhere in the world."
The Christchurch Earthquake, meanwhile, produced exceptionally high ground shaking for a relatively moderate-sized earthquake, demonstrating how devastating a 6.3 earthquake could be when it was shallow, close to a populated area, with energy directed straight at the city, and geologic conditions that amplify the shaking.
Ristau said his big takeaway from the decade was to expect the unexpected.
"Over the last decade the Alpine Fault has been the one that has been considered most at risk of rupturing in a major earthquake in the near future," he said.
"Instead we had a 7.1 earthquake along a fault that hadn't ruptured in about 20,000 years, at Darfield, and a 7.8 earthquake of unprecedented complexity on the opposite coast."
Was there any simple reason for all of that activity?
"Over the last 170 years, which is about the longest historical record we have of major earthquakes in New Zealand, there have been periods of heightened significant earthquake activity and quieter periods," Ristau said.
However, he added, over millennia, it was quite possible we would see an entirely different pattern - so it was difficult to put too much emphasis on recent history.
"We can say that in the last 20 years there have been more major earthquakes in New Zealand than the previous 50 years, but we can't say it's due to anything other than coincidence," he said.
"Unfortunately, we have no way of knowing what the next decade will hold."
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