Earthquake record in 2016

Earthuakes were prominent in news in 2016 and for good reason – not only was there on of the biggest recorded earthquakes in New Zealand history, there were a record number of earthquakes recorded.

Number of earthquakes:

  • about 20,000 on average per year
  • 29,000 recorded in 2011 (a bad year in Christchurch)
  • 38,828 earthquakes recorded in 2016

This is a big jump but it’s not really surprising given the chain reaction across multiple faults in the North Canterbury shakes last year.

Most of those were recorded by sensitive instruments and wouldn’t have been felt, but there were still quite a few that shook enough to be noticed.

  • 7.0 or more – 2 (7.8 and 7.1)

Geonet: 2016 in review: The Groundbreaker

The M.7.8 Kaikoura earthquake will not go into the global history book of earthquakes because of its magnitude; the Ring of Fire regularly gets that size and much larger earthquakes. What makes it unique is two things: how it ruptured across the faults through the North Canterbury and Marlborough Fault areas and the slow-slip earthquakes triggered by M7.8.

  • 6.0-6.9 – 10
  • 5.0-5.9 – 122

Geonet Facts and Stats:

Frequency of New Zealand Earthquakes (1960 to 2015)
Magnitude Annual Average Minimum Maximum “Rule of Thumb”
4.0 – 4.9 451 184 1,343 1 per day
5.0 – 5.9 51 19 127 4 per month
6.0 – 6.9 2.7 0 9 5 per 2 years
7.0 – 7.9 0.4 0 2 1 per 2.5 years
8.0 or over 0 0 0 1 per century*
* Based on geological investigations and historical record of earthquakes.

So there were significantly more than average in 2016.

There have been many images of the many fault lines, land slips and broken land.

The latest images were taken from planes by Land Information New Zealand (Linz) and the NZ Transport Agency (NZTA), and are  here.

Stuff has some before and after slide views in Before and after the Kaikoura quake: images show colossal damage.

 

Earthquakes haven’t gone away

People in North Canterbury, Marlborough and the Wellington region, and further afield,  were reminded that the earthquake onslaught isn’t over yet. The more significant quakes over the weekend:

  • 4.6 (strong) 30 km south-west of Wellington – Sat, Nov 26 2016, 3:22:03 am
  • 5.1 (severe) 35 km north of Wairoa – Sat, Nov 26 2016, 8:21:42 pm
  • 3.9 (moderate) 20 km south-east of Culverden – Sun, Nov 27 2016, 8:25:29 pm
  • 4.5 (moderate) 35 km west of Paraparaumu – Sun, Nov 27 2016, 9:31:11 pm
  • 4.1 moderate) 20 km south-east of Seddon – Sun, Nov 27 2016, 9:33:28 am
  • 3.7 (moderate) 10 km south-west of Kaikoura – Sun, Nov 27 2016, 7:46:44 pm
  • 4.8 (strong) 15 km east of Seddon – Sun, Nov 27 2016, 9:42:16 pm
  • 4.1 (moderate) 20 km south-east of Seddon – Sun, Nov 27 2016, 10:05:32 pm

The latest from 7 am update:

  • 125 earthquakes in last 12 hour
  • 220 earthquakes in last 24 hrs (4 over M4)
  • 6159 earthquakes since the M7.8 Kaikoura Earthquake.

geonet2016november28

So while in general the frequency and size of the quakes is gradually easing off it is not all over yet, and periodically some bigger quakes come back to remind those in the shaking region.

Geonet still predicts an 81% chance of an M6-6.9 shake in the next 30 days and 99% in the next year, and a 34% chance of a greater than M7 in the next year.

Geonet: Latest Updates and Scenarios and Probabilities

No imminent ‘large aftershock’ threat

The multi region structure of Civil Defence showed it’s weakness again yesterday when West Coast Civil Defence warned people to prepare for a ‘large aftershock’, but this was talked down by the Ministry of Civil Defence and Geonet, who said their information had been misinterpreted.

West Coast Civil Defence have since retracted their warning.

Aftershocks are normal after large earthquakes. So far there have been over 5,000 aftershocks following the Culverden-Kaikoura-Seddon M7.8 earthquake on Monday last week.

6.30am update: 7 eq in last hour, 156 eqs in last 12 hrs ( only 2 over M4) and 5456 eqs since the M7.8 Kaikoura Earthquake – @Geonet

They seem to be following a normal pattern of reduced frequency and size with a few bigger  blips.

Geonet have made general predictions of aftershocks based on statistics, which includes the likelihood that there will be large aftershocks some time. But it is not possible to accurately predict how big, nor when.

Regardless of the uncertainty people throughout New Zealand should be prepared for any earthquake event.

Newshub: National Civil Defence says no imminent ‘large aftershock’ threat

West Coast Civil Defence Public Information Manager Andy Thompson earlier said the aftershock activity in the area been “suspiciously quiet”.

“The GeoNet seismograph drums have been very quiet for the last day or so and the normally higher aftershock sequence of large quakes has not been occurring in the Kaikoura area,” said a statement from West Coast Civil Defence.

West Coast Civil Defence regional manager Chris Raine said another worry is that an area in Arthur’s Pass slightly west of the divide has experienced a number of small tremors in the last few days.

He said it’s an area they have been monitoring closely, with Mr Thompson describing it as “highly sensitive”.

West Coast Civil Defence has staff on duty this weekend to be available in the case of aftershocks and the forecasted heavy rain that is expected to start tomorrow morning.

They are urging locals to stock up on enough food, water, cash and medicine to last a week, and to ensure they have an emergency plan in place.

“If an earthquake is so strong that people can’t stand up, or rolling lasts more than a minute, they should evacuate inland,” regional manager Chris Raine said.

 The problem isn’t with the advice, but with the warning of an imminent large aftershock in their region.

But GeoNet say the science they’re using to authenticate the warning is simply incorrect.

“Just because the drums have been quiet for a day means absolutely nothing,” GeoNet seismologist John Ristau said.

“We kind of want to distance ourselves from this – we don’t know why they’ve gone out and done this.”

Mr Ristau says it is not usually Civil Defence’s policy to issue a warning without checking in with them first.

“Civil Defence would talk to us, we advise them, and they would never release anything without talking to us.

“What [West Coast Civil Defence] have done is looked at our [seismograph] drums, and taken the information we’ve put out and made their own interpretations.”

The Ministry of Civil Defence’s head office was also bemused by what was put out by the West Coast offshoot when contacted by Newshub, with a spokesperson saying they’re not aware of any increased risk of a strong aftershock.

The spokesperson reiterated that they are in regular contact with GeoNet, and would seldom issue a warning without consulting them first.

@Geonet tweeted at 7:13 last night:

Reminder: We produce forecasts and scenarios NOT specific eq warnings regarding aftershocks. if you see an eq warning, it’s not from GeoNet

Followed by

Contrary to some reports the Ministry of Civil Defence has not issued an earthquake threat warning for West Coast

On Facebook yesterday at 7:18 pm::

Please share this with anyone you know who is worried.

Contrary to some reports there is no “imminent threat” to the West Coast from earthquakes. Neither have we issued an earthquake threat warning.

After a large earthquake there is always an increased likelihood of aftershocks, some of which may be large.

Remember: drop, cover and hold until the shaking stops.

If you feel a strong earthquake that makes it hard to stand up, or a rolling earthquake that lasts longer than a minute, or observe strange sea behaviour such as the sea level suddenly rising and falling, or the sea making loud and unusual should move immediately to high ground, or as far inland as possible.

Since Monday GeoNet have been issuing earthquake forecasts based on the best science they have available – their most recent one can be found here: http://info.geonet.org.nz/…/M7.8+Kaikoura+Quake%3A+Future+S…

 And they followed up at 22:05 pm:

On our previous post: West Coast Civil Defence Emergency Management have retracted their urgent warning around large aftershocks on the West Coast. Media ran their stories in good faith and we thank them for running clarifications.

Remember – after a large earthquake there is always an increased likelihood of aftershocks, some of which may be large. Check out our previous post for more advice on what to do in quake.

You can find the latest earthquake forecasts from the good folk at GeoNet

The disjointedness between Geonet, national Civil Defence and all the Civil Defence regions is messy and needs to be tidied up.

West Coast Civil defence have now retracted their urgent warning.

Stuff: Large aftershocks a possibility, but there are no ‘urgent warnings’

West Coast Civil Defence Regional manager Chris Raine initially refused to answer questions from the media about the release, saying he was not prepared but was dealing with the fallout with the ministry. 

From his home in Greymouth, he said he accepted people were concerned after the release was issued and apologised.

“I apologise. It was done in the best interests of the West Coast people,” he said.

“I withdraw the urgent warning completely.”

He added Thompson, who issued the release, may have “misinterpreted” the risk of aftershocks.

This is ridiculous. The only thing missing is a full moon.

Each local emergency management office was responsible for its region, Clifford said. The Ministry for Civil Defence was a “central coordinator” for emergency responses, she said.

“The West Coast have a responsibility for their community and they have acted in what they think is the best for their community,” Clifford said.

She urged people to follow the information and advice issued by GNS Science and the Ministry of Civil Defence.

“The press release that has come from West Coast was not sent on behalf of the ministry,” she said.

The current disjointed way that Civil Defence advises the public is hopeless. And poor.

The West Coast Civil Defence website gives no obvious indication of any of this, it seems to have all happened via media.

This is hopeless. Where should we look for up to date information and warnings on earthquakes? I have no idea.

The national Civil Defence website has general information but nothing specific. Their last News and events ‘new update’ is remarkably dated 10 November, before any of these earthquakes occurred.

We should all know exactly where to go online for the latest information and advice.

Earthquake problems continue

Most of New Zealand has more or less put the earthquakes behind them,  but there are significant ongoing problems.

An aftershock in North Canterbury yesterday evening seriously damaged houses and forced evacuations, and also held up access to Kaikoura via the inland route.

There is no sewerage system in Kaikoura, they are running out of water and fuel, and frustration grows for those who want to get out by road but aren’t allowed.

This afternoon Goose Bay was evacuated after a warning a slip created dam might burst.

The NIWA building in Wellington was shut today pending a proper building inspection.

And tonight another building in Wellington was evacuated due to fears that it’s stairwells were damaged.

RNZ: Wgtn’s Asteron Centre evacuated over quake risk

Wellington’s 17-storey Asteron Centre has been evacuated over possible earthquake damage to its stairwells.

The high-rise, described by its designers as the capital’s largest single office building, is located opposite the Railway Station.

Updates from Geonet continue.

This simulation shows how the seismic waves of the magnitude 7.8 earthquake were propagated across New Zealand.

This also shows how the initial quake dominoed it’s way up the South Island from Culverden to Seddon: Watching the M7.8 Kaikoura Quake Dominos Fall in Real Time

And  How is the Kaikoura aftershock sequence behaving compared to the forecast?

By noon on Wednesday 23 November we had detected 4879 aftershocks from the M7.8 Kaikoura earthquake (with the area of detection being the forecast area represented by the box). 

Most of these aftershocks have been small (4828 earthquakes <M4.9) and would have only been felt close to the epicentre.

As of Monday 21st, there were also 47 aftershocks in the M5.0-5.9 range, and 3 aftershocks in the magnitude M6.0-6.9 range.

That sounds a lot but:

At the moment, the aftershock sequence is falling within the lower end of our forecasted range.

What does this mean?

In summary, the aftershocks are at the lower end of the forecasted range. It is a bit puzzling and we are scratching our heads at this one. What we can say is that just because we are in lower end of the forecast, it doesn’t mean that this will stay that way.

Pretty much anything could happen from here, from less and less to substantially more.

All we can do is be wary and be prepared.

Measuring the ground movement

Geonet have been busy measuring how much the ground moved in this week’s earthquakes (it is still moving in some parts).

GPS allowed rapid detection of land movements due to M7.8 earthquake

Within a couple of hours of the M7.8 earthquake, GeoNet was able to use the GPS data to estimate the initial displacements of the Earth’s surface that occurred during the earthquake.

kaikouraearthquake_web_18nov2016

What the GPS revealed was astonishing. It turns out that the earthquake shifted the land at Cape Campbell (the northeast tip of the South Island) to the north-northeast by more than 2 m, and up vertically by almost 1 m.

This means that Cape Campbell is now more than 2 m closer to the North Island than it was before the earthquake. Similarly, Kaikoura has moved to the northeast by nearly a metre, and has been lifted upwards by 70 cm.

Hanmer Springs, which was our closest GPS site to the quake epicentre, jumped eastward by approximately 50 cm. All of this movement happened during the earthquake in a matter of seconds.

A lot more of the country moved to a lesser extent.

Not only did the earthquake shift landmasses in the northern South Island, but it also caused movements across most of the country.  

gps3

In the lower North Island, the east coast has shifted west by 1-5 cm, while the Wellington and Kapiti regions were shunted 2-6 cm to the north. Christchurch and Banks Peninsula didn’t miss out on the action, either—they are now approximately 2 cm further south than they were the day before the quake.

Some parts of the west coast of the South Island have been shifted eastward by as much as 10 cm. The northern North Island and southern South Island only moved a few millimeters.

Satellite mapping shows horizontal movements.

cViewing the M7.8 Kaikoura earthquake from space

A technique called InSAR, which stands for ‘Interferometric Synthetic Aperture Radar’, utilises radar satellites orbiting ~700 km above the earth to precisely measure the distance between the ground and the satellite. If the ground moves between two subsequent satellite passes, due to an earthquake or volcanic eruption, then the distance between the ground and the satellite changes. Observing these changes in the positon of the land with InSAR enables us to generate detailed maps of ground movement, often with centimeter-level accuracy.

The satellite images reveal huge changes in land movement across the Hope and Kekerengu faults, as well as several other faults in the region. 

To the east of these faults, the land went mostly southwest (see blue area in the figure on the left). In contrast, to the west of these faults the land moved mostly northeastwards (see red area in figure on left).

Sharp changes in land movement are visible on the InSAR images, and show us where the faults ruptured to the Earth’s surface.

insar_1_cropped

Horizontal offsets from radar data. The red colours show up to 5 m of horizontal motion of the land towards the north-east and blue colours show up to 6 m of land movement to the southwest. The yellow lines show faults that appear to have ruptured.

insar_2_wtrmkd

An interferogram generated using data from a Japanese Space Agency satellite. Each set of rainbow-coloured contours represent 11.5 cm of movement. Where the colored contours are closest together is where the largest changes in land motion are occurring.

These are different ways of showing ‘much munting’.

And there is likely to be more to come, although hopefully to a lesser extent.

Earthquake update – Thursday

Geonet 5 am Thursday update:

  • 19 earthquakes in last hour
  • 290 earthquakes in last 12 hrs (11 over M4)
  • 2070 earthquakes since the M7.8 (570 since 4 am Wednesday)

The rate and size of quakes is slowly reducing. The larger quakes overnight:

  • 4.3 – 7:45:51 pm 20 km south of Seddon
  • 4.3 – 7:46:33 pm 20 km north-east of Kaikoura
  • 3.8 – 9:27:10 pm 5 km north of Culverden
  • 4.8 – 10:15:14 pm 20 km east of Martinborough
  • 4.3 – 1:19:45 am 30 km north-east of Arthur’s Pass
  • 3.8 – 3:20:09 am 25 km north-east of Hanmer Springs
  • 4.0 – 3:41:33 am 30 km south of Seddon
  • 4.9 – 4:03:49 am 20 km south-west of Kaikoura
  • 4.0 – 5:02:32 am 10 km north of Culverden

Notable points: while reducing in size they are still spread over the three main areas, Culverden/Hamner, Kaikoura and Seddon, but with two other locations, east of Martinborough on the Wairarapa faultline (the one that went M8+ in 1855) and one north-east of Arthur’s Pass (Alpine Fault territory).

We can hope that these are reducing stresses rather than increasing them on other faultlines.

Yesterday Geonet upgraded the size of the initial quake (which may have been two consecutive quakes in different locations) from M7.5 to M7.8.

Kaikoura earthquake update: Magnitude revised

What has changed since our initial review

Based on our findings and in discussion with international researchers, early indications are that this is one of the most complex earthquakes ever recorded on land. This complexity means we have had to take extraordinary efforts to determine the magnitude, depth, and locations.

The very long time it took for the faults to rupture (over one minute) meant that the standard methods of calculating magnitude were insufficient to capture the full energy released.  

Due to the size of the quakes, we’ve gathered data from our entire network of seismic stations. All of these stations would not normally need to be included in magnitude estimates.

Further, our techs at GeoNet went out to several sites which we lost communication with and we have now been able to upload this information, so we have a more complete understanding of the ground deformation and strong-motion data.

Finally, our science teams have been working tirelessly, going up and down the affected areas and measuring the length of faults and how much they moved.  Their efforts have provided us with a clearer picture as to the size and length of the ruptures.

Based on all these ongoing efforts, we can say with some confidence that the earthquake was an M7.8.  This is consistent with estimates from several  other international agencies, specifically the USGS. Their early model provided us important information and we used all our additional data sets to confirm the magnitude. 

What this means

The new magnitude just tells us what we think most people who felt the earthquake already know: it was powerful, and went on for a long time over a large distance. It doesn’t change what happened but it does provide us with more knowledge about how significant the event was.

Our recent analysis confirms the complexity of this event. It does not change any of the observations of strong ground motion, fault breaks or GPS recorded movement of the earth’s surface – these are physical observations independent of the magnitude of the earthquake.

We are in the process of revising our probabilities and scenarios based on this new information and should have this released within the next 24 hours.

RNZ continues to have good coverage, including:

Rescue efforts in Kaikoura continue as helicopters and NZ and US defence force ships arrive in the quake-hit town with supplies.

Wellington is also dealing with the aftermath of Monday’s 7.8 magnitude quake, with several central city buildings deemed unsafe.

The aftermath of the 7.8 magnitude quake so far

Govt to consider funding for 24/7 quake monitoring

‘Absolutely gutted’: Tiny community of Mt Lyford devastated by quake

 

 

 

 

 

Earthquake upgraded to 7.8

Gerry Brownlee has informed media that Geonet Science have upgraded Monday’s initial earthquake from 7.5 to 7.8, making it officially a whopper.

This makes it a similar size to the largest shocks recorded in New Zealand:

  • M 7.8, Dusky Sound, 15 July 2009The earthquake which struck the Fiordland region in the evening of Wednesday 15 July was the biggest since the Buller and Hawke’s Bay earthquakes of 1929 and 1931.
  • M 7.8, Hawke’s Bay, 3 February 1931The 1931 Hawke’s Bay earthquake caused the largest loss of life and most extensive damage of any quake in New Zealand’s recorded history.

That last one, from 1855, caused extensive damage and ground upheaval around Wellington.

This upgrading has followed recalculations of what was a complex combination of shocks. It will lead to upgrading of probability predictions of more and larger after shocks.

USGS had always rated it at that: M7.8 – 53km NNE of Amberley, New Zealand

The November 13, 2016 M 7.8 earthquake in North Canterbury, New Zealand, occurred as the result of shallow oblique-reverse faulting on or near the boundary between the Pacific and Australia plates in South Island, New Zealand. 

The complexity of the event, involving a main energy release delayed by about 40 s, combined with an early aftershock distribution extending about 150 km to the north-northeast of the mainshock, suggests the potential for triggered slip on the Pacific:Australia subduction zone interface.

This matches current Geonet explanations that the initial quake, which last for 30-40 seconds probably triggered and was followed by a chain reaction moving north east affecting multiple fault lines, now thought to be at least 6.

This map shows revised understanding of that fault system in relation to the shocks.

kaikoura-earthquake-faults-e1479265716143

The Kaikoura earthquake

Commonly large earthquakes break a single fault in the earth’s crust and aftershocks occur in a focused area around that fault as the crust adjusts to the movement. Monday’s event was much more complicated. The location of aftershocks and field observations of where the crust has broken (see map) indicate that earthquakes occurred on more than one fault.

Already, it looks as though parts of well-known faults such as the Hundalee, Hope and Kekerengu Faults have ruptured (broken) and also parts of less well-known or unknown faults around Emu Plains, The Humps Fault zone and Waipapa Bay have also ruptured. Such a sequence of earthquakes occurring on different faults in such a short time-frame has not been witnessed before in New Zealand. There will be many types of data and days of collection and analysis required to make sense of what happened and what the implications of this earthquake sequence are for the future.

The Spinoff has more explained by GNS Science geologists Nicola Litchfield in This stunning map shows that six faults – at least six – ruptured in the big Kaikoura quake

That’s a lot of faults.

Yes. Usually you expect one big earthquake on one big fault, but like in the Christchurch earthquakes, and in fact we saw this in Edgecumbe in 1987, we often get these complex ruptures, where multiple faults rupture in the one earthquake. But this was a bit of a surprise, as to how many and which ones have ruptured.

Do we know which one went first?

The earthquake started in the south. So the big red dot, the M7.5, that’s the epicentre of the first earthquake, so we’re pretty certain that the faults just to the north of that – the Emu Plains, the Humps fault, the Hundalee fault – went first, then it continued up the coast, up to, a little bit on the Hope fault but particularly the Waipapa Bay and the Kekerengu fault went second.

I certainly felt that in Wellington: when I woke up I felt two parts to the earthquake, and we think that’s what happened, we had a southern part and then a more northern part.

I think the first part, the southern part, was about 30 seconds, and then followed immediately afterwards by the ruptures up to the north. Most people would consider that just one big long earthquake.

Does each one of those ruptures cause its own aftershocks?

Yes, you can see the cloud of aftershocks that have happened and they’ll be focused around all those faults.

More to come on this no doubt, for those who are interested in the details.

In the meantime a road from the south to Kaikoura has been opened, but is open to ‘army grade 4 wheel drive vehicles’ so it is not open to the public.

Earthquakes – Wednesday update

The earthquakes are continuing, now generally fewer and smaller, often seeming in pairs near Seddon and Kaikoura, and at times in triplets with Culverden/Cheviot/Hamner Springs in the mix.

Geonet had an update at 4 am:

  • 23 earthquakes located in the last hour (Wednesday morning)
  • 278 earthquakes since 6 pm (Tuesday)
  • 1,492 earthquakes  since the M7.5 Kaikoura Earthquake (just after midnight on Monday).

Alan was in Hamner Springs when the M7.5 struck:

I was in Hanmer in a wooden Fraemohs chalet trying to fix my phone while my wife watched a TV movie when the first big 7.5 hit. I have to say the chalet was great – strong as a boat in a storm as we rocked and rolled. It was built on a good thick concrete pad and the interlocking beam walls performed perfectly.

We had driven through the epicentre at Waiau that afternoon and stopped for a few minutes of course never guessing anything so drastic was about to happen there.

While it was happening I was standing back to a window which in retrospect although it had a heavy curtain was probably not a great idea but it was too far to get around the bed to the passageway while keeping my balance while it was like being on a yacht in a choppy sea with a howling wind.

The noise was like a train or a plane roaring past right outside.

I have heard people from Christchurch describe the bigger earthquakes as like a train roaring past right outside their house. I’ve never been close enough to a big one to hear one (I’m not complaining).

After that I could hear the aftershocks coming as a low frequency sound just before they started but my wife couldn’t. She hears higher frequencies better than me though.

Power went out in the middle of the quake and didn’t come back till midday the next day but the road out didn’t open till 4pm the next day.

Alan was lucky the road was openable. One of the remarkable things about these earthquakes, presumably mainly as a result of the huge M7.5, is the widespread destruction of roads – not just the huge slips on the Kaikoura coast but so many roads have been ripped apart, like this one in Waiau.

state-of-road-in-waiau-after-earthquake-supplied

There have been many movements of land, ripped apart, buckled and raised and lowered.

kaikouraseabedraised2

Aerial photographs show the seabed uplift north of Kaikoura – estimated to be between 2 – 2.5 metres – more at @TonkinTaylor – which also shows minor road slips.

Media seemed to obsess over the trapped cows yesterday morning – they were rescued – but now the poor paua are being pitied, raised out of the water and dying.

Newshub: Baby paua suffering terrible deaths in sun

It’s not just the thousands of exposed paua that are a high concern in Kaikoura – exposed baby paua are also dying by the hour.

The paua have now been exposed out of water for more than two days after the seabed was lifted nearly two metres out of the water by Monday’s 7.5 earthquake.

Paua Industry Council’s Storm Stanley says there’s a lot of worry for the tens of thousands of adult paua but people forget about the babies.

“What you won’t see are the smaller paua that live under rocks. They live under rocks until they’re about 16, 17 millimetres long before they come out again,” he says.

pauaraised

Nature can be brutal.  It’s tough on the paua and other exposed sea life on the fishing industry, but I suspect there are more pressing problems for most people to attend to.

RNZ have today’s key facts:

Rescue efforts in Kaikoura continue as helicopters and NZ and US defence force ships head to the quake-hit town with supplies.

Wellington is also dealing with the aftermath of Monday’s 7.5 magnitude quake, with a city centre building at risk of collapse.

As usual they are covering things extensively – see RNZ continues live online coverage here.

Geonet: M7.5 Kaikoura Earthquake: for more information read Latest Updates and Scenarios and Probabilities.

Damaged buildings in Wellington is becoming a big story of it’s own – that’s for another post.

Earthquakes continued…

Quakes have continued to rumble through the night in the north east of the South Island, with 28 recorded at Geonet in the last hour (4:20 to 5:20 am). There have been about 800 aftershocks altogether.

There are reports that there could be up to 100,000 landslides/slips.

Geonet says that multiple faults have ruptured:

Rapid field reconnaissance indicates that multiple faults have ruptured:

  • Kekerengu Fault at the coast – appears to have had up to 10m of slip
  • Newly identified fault at Waipapa Bay
  • Hope Fault – seaward segment – minor movement
  • Hundalee Fault 

What we are finding in New Zealand is that quite a few of our larger earthquakes involve jumping from rupture on one plane to another in a complex sequence.

‘Strong’ or ‘severe’ quakes overnight (these seem to have slowed down):

  • 5.0 (severe) 10:49:56 pm 10 km east of Kaikoura
  • 5.1 (strong) 12:16:42 am 15 km east of Seddon
  • 4.8 (strong) 1:03:00 am 5 km west of Kaikoura
  • 4.6 (strong) 4:22:19 am 10 km east of Seddon

So both Kaikoura and Seddon continuing to bear the brunt of this. Those are moderate sized quakes on the scale but they are shallow (8-25 km) so more energy gets to the surface than deeper quakes.

This map shows the pattern of quakes since midnight yesterday. Most of them are shallow.

earthquakes2016novdepthmap

Earthquakes midnight 14 Nov – 5:30 am 15 Nov (Geonet)

And this shows their strengths better:

earthquakes2016novstrength

Last 500 earthquakes light to severe as at 6:oo am 15 November 2016 (Geonet)

That shows the clustering in North Canterbury-Marlborough with a couple in Wellington but they feel the bigger Seddon quakes in Wellington too.

Updates from Geonet:

M7.5 Kaikoura Quake: What we know so far

Updated at 23.52, 14/11/2016 This earthquake was the largest recorded in New Zealand since the M7.8 Dusky Sound earthquake in 2009. But, given its location, it was more widely felt and more damaging. This earthquake unsettled many people and that is perfectly normal; earthquakes can be upsetting events. The best advice we have is to be prepared for earthquakes.  We can say one thing with certainty: there will be more earthquakes to come in this area.…

M7.5 Kaikoura Earthquake: Latest updates

Multiple ruptures

Rapid field reconnaissance indicates that multiple faults have ruptured:

  • Kekerengu Fault at the coast – appears to have had up to 10m of slip
  • Newly identified fault at Waipapa Bay
  • Hope Fault – seaward segment – minor movement
  • Hundalee Fault 

In the simplest case an earthquake is a rupture on a single fault plane.

What we are finding in New Zealand is that quite a few of our larger earthquakes involve jumping from rupture on one plane to another in a complex sequence. We first saw that with the Darfield Sept 2010 EQ where multiple segments ruptured together as a single earthquake. We appear to have seen this again overnight.

In terms of what might happen next: The scenarios provide an overview of how we see this earthquake sequence evolving over the next few days to one month. What is on the web page is our best information that we have to hand at the moment.

We’ve developed three scenarios based on what we know so far but be aware that our understanding is evolving as we do more analysis and receive more data. 

Scenario One: Very likely (80% and greater)
A normal aftershock sequence that is spread over the next few months to years. Felt aftershocks (e.g. M>5) would occur from the M7.5 epicentre near Culverden, right up along the Kaikoura coastline to Cape Campbell over the next few months to years. This is the most likely scenario.

Scenario Two: Likely (60% and greater)
In the next month, it would be likely that rupture of earthquakes of about an M6 in the North Canterbury and Marlborough regions will occur, as well as potentially offshore in Southern Cook Strait and offshore Kaikoura.

Scenario Three: Unlikely (less than 40%)
The least likely scenario is that in the next month, (it is unlikely but still possible) there would be rupture of longer known faults (with earthquakes of about M7), in the Marlborough and Cook Strait regions.

So there is at least likely to be a continuation of the many aftershocks, with the lower possibility of some quite large ones still to come.

Strong aftershocks

There were more strong aftershocks off East Cape overnight following last week’s 7.1 earthquake, with a 5.7 at 3:19 am followed by a 5.3 at 5:01 am, plus a bunch of smaller earthquakes.

Here are the 5+ quakes in that region over the past week.

  • 5.7 – Thu, Sep 1 2016, 10:04:35 am, 100 km north-east of Te Araroa
  • 7.1 – Fri, Sep 2 2016, 4:37:55 am, 125 km north-east of Te Araroa
  • 6.2 – Fri, Sep 2 2016, 5:14:05 am, 110 km north-east of Te Araroa
  • 5.7 – Fri, Sep 2 2016, 7:18:28 am, 90 km north-east of Te Araroa
  • 6.0 – Fri, Sep 2 2016, 8:06:03 am, 125 km east of Te Araroa
  • 5.5 – Sat, Sep 3 2016, 4:30:10 pm, 70 km east of Te Araroa
  • 5.5 – Sun, Sep 4 2016, 1:30:26 am, 65 km east of Te Araroa
  • 5.1 – Mon, Sep 5 2016, 8:00:28 am, 55 km east of Te Araroa
  • 5.7 – Tue, Sep 6 2016, 3:19:01 am, 95 km north-east of Te Araroa
  • 5.3 – Tue, Sep 6 2016, 5:01:58 am, 95 km north-east of Te Araroa

There have also been many smaller quakes, about 15 greater than 2 so far this morning.

A map showing the pattern of quakes.

QuakeMapEastCape

Fortunately the bigger ones are all offshore. Hopefully this is all easing stresses in the Pacific/Australian plate collision.

There’s good reasons for New Zealand to be known as the Shaky Isles.

From Geonet:

deep_seismicity1

The pattern of deep earthquakes in New Zealand. The two subduction zones are clearly seen: under the North Island and at Fiordland.

There looks to be a big gap waiting for the big one, but shallow quakes are more spread:

shallow_seismicity

The pattern of shallow earthquakes in New Zealand. Although earthquakes are seen occurring along the junction of the two tectonic plates and also feature around the volcanic regions, they can occur anywhere in New Zealand.