NZ earthquake 14.11.16 - Mag 7.8

[CapnGranite]

Continent-scale strike-slip on a low-angle fault beneath New Zealand's Southern Alps: Implications for crustal thickening in oblique collision zones
http://onlinelibrary.wiley.com/doi/10.1002/2015GC005990/full

This site summarizes what's in the paper. Most of the research on the Alpine fault has been south of the area of the recent quakes, but this newish study might help explain the seemingly odd distribution of aftershocks.
http://blogs.agu.org/geospace/2015/...-for-rethinking-of-new-zealands-alpine-fault/

Of general interest:
http://www.victoria.ac.nz/news/2016/03/new-zealands-alpine-fault-biggest-mover-in-the-world

 

[CapnGranite]

Because of similarities to the San Andreas Fault, the Alpine Fault has been studied by geologists studying the SAF and the the larger transform system that it is part of. In the past week I've come to appreciate just how much more complicated the Alpine Fault is in relation to the plate boundaries compared to what's going on in California.

 

[cosmik debris]

When I woke up because of the quake (I'm in Lower Hutt), I thought it would stop. But it got more intense and once I heard things falling down in other rooms, I thought 'this isn't good'. I expected that the quake was located quite near Wellington. It did go through my mind that the house could collapse, once I heard things falling. I -cannot- imagine what it was like down in Christchurch 2010 and 2011.

It was pretty bad in 2010 - 11, the G forces, because the epecentre was almost directly below the city were very high which caused a lot of damage. The quakes were short but very violent. The lack of high frequency components this time were a good indicator that the quake wasn't local. I feel for you people because it is the months of aftershocks that wear you down, the lack of sleep makes the whole population irritable and in our case lasted for a good 18 months. You walk into a new building or room and immediately look for anything that could kill you. And then there is the insurance companies to deal with...

 

[cosmik debris]

This is scary: http://www.stuff.co.nz/national/86497605/Concerns-over-building-stability-in-central-Wellington
And the building which houses staff for Statistics NZ is declared unsafe, and it may be a year before they could re-enter. Little detail has been shared about how it is inside, they believe some concrete beams have fallen.

This is a very worrying state of affairs for a city that in many ways is more susceptible to a bad quake than many. I hope questions are asked. The deaths that occurred in Christchurch need not have happened if the buildings had been designed and built properly, and there is no reason why a relatively modern building should not be safe.

 

[StevieTNZ]

It appears that the earthquake on Monday at 12.02am has been upgraded from 7.5 to 7.8

"GNS Science has revised the magnitude of the large earthquake that struck at 12:02am on Monday from a 7.5 to a 7.8."

Live updates can be found here -- http://www.stuff.co.nz/national/86416304/live-north-canterbury-quake

 

[StevieTNZ]

@jtbell and all those concerned: the cows are now safe.

 

[davenn]

Yeah! I was checking geonet.org.nz and I saw all these earthquakes after the 12.02am happening around the country... one even by Levin!

GeoNet says the massive 7.5 earthquake overnight seemed so long was because it was two quakes, not one - lasting a combined two minutes and triggering a swarm of frightening aftershocks.

.

As I noted in an earlier comment this is a possibility, but it isn't the only cause of long duration shaking.
Once the chaos has died down a bit in the Seismo Obs at GNS, I would really like to query them on that statement and hopefully get a response as to why they think that?. I really think it may have been made in haste, considering at the time, they estimated a magnitude much smaller than what it really was. This meant the smaller size couldn't account for the shaking time that a larger event would have and they had to come up with a reason.

The other common cause is by the rupture mode. The 2 main ones are uni-lateral and bi-lateral. The significant difference is that a uni-lateral rupture will produce twice the shaking period as a bi-lateral rupture
Uni-lateral --- Rupture on the fault starts at one end of the rupture zone and propagates primarily in a single direction
Bi-lateral ----- Rupture on the fault starts roughly in the middle of the rupture zone and propagates roughly equally in both directions

Lets initially ignore the cluster of events up of the Cape Campbell area as they are associated with different fault(s). We will look at the main shock, SE of Hanmer Springs and the following aftershocks that trend to the NE through the Kaikoura region and then offshore. In the case of this event, neither the seismograms, nor the aftershock sequence suggest a multiple event. Rather they both suggest a single event and most likely a uni-lateral rupture.
It can be seen from the aftershock distribution that there are very few events to the SW of the main event. The vast majority of them are to the NE, up to and off the coast beyond Kaikoura.
The rupture has most likely to have occurred on the Hope Fault that I have high-lighted in yellow. Don't be too put off by the designated locations of the events relative to the fault, there is going to be a reasonable error in their location and also, since they were a little deeper (~ 25 - 35km), some of them ( including the main event) could well have been down dip on the fault plane to the south east.

At this time, I am pretty confident that the Hope Fault will be the nominated source of the event. It's the only obvious major fault in the area. I would suggest that, tho it is possible that the event occurred on some hidden fault line, it would be highly unlikely.
Considering the size of the event, it is...
1) likely that wouldn't have been the first event throughout history
2) would require the presence of a major fault that is unlikely to have remained hidden for millions of years.more to come ...

 

[CapnGranite]

This article seems to put the seismic activity into some perspective:
http://thespinoff.co.nz/science/16-...-at-least-six-ruptured-in-the-kaikoura-quake/

 

[davenn]

This article seems to put the seismic activity into some perspective:
http://thespinoff.co.nz/science/16-...-at-least-six-ruptured-in-the-kaikoura-quake/

There are problems with some of that

specially the fact that none of those smaller faults could produce a M7.8 event ... that requires a larger fault like the Hope Fault

I am pleased that they confirmed my uni-lateral rupture mode

I have no issue with the multiple minor faults activating and even rupture hopping between several more significant faults.
That isn't unheard of, a classic example is the Southern California, M 7.3, Landers quake of 1992 ...
This event was a uni-lateral rupture that jumped across several faults as it propagated to the NW.

here's another article on the NZ event

http://blogs.agu.org/tremblingearth...w-zealand-earthquake-part-1-seismology-night/

 

[StevieTNZ]

This is really really shocking http://www.stuff.co.nz/national/nz-...ngs-cordoned-off-over-earthquake-safety-fears

The amount of buildings off limits is going to bring the city to a stand-still.

 

[Astronuc]

From a related article - The Kaikoura earthquake lifted long strips of coast out of the sea on Monday morning, in parts as high as two metres.
http://thespinoff.co.nz/featured/17...es-out-of-the-ocean-coastal-uplift-explained/

Much of the northeastern coast of the South Island was uplifted during the 14 November earthquake. We know this from photos of rock platforms covered in seaweed and marine animals such as crayfish and paua stranded above tide levels. Our records measured the tide gauge at Kaikoura was lifted up by one metre, and continuous GPS monitoring sites at Kaikoura and Cape Campbell were also raised by 0.7-0.9 m. At this stage we can estimate that the coast was raised between 0.5 m and 2 m from about 20 km south of Kaikoura all the way north to Cape Campbell.

That's impressive!

Of course, it's better than the opposite.Possibility of another large earthquake in future - but where?

Geonet has released newly calculated aftershock probabilities that put the chance of one or more M6-6.9 quake in the next day at 37%.
http://thespinoff.co.nz/society/15-...t-probabilities-of-major-eqnz-in-coming-days/

A few of NZ's larger earthquakes involve jumping from rupture on one plane to another in a complex sequence. It was first seen with the Darfield September 2010 quake where multiple segments ruptured together as a single earthquake. It appears to have been the case in the Kaikoura earthquake.

Some probabilities of future quakes are given.

 

[cosmik debris]

This is really really shocking http://www.stuff.co.nz/national/nz-...ngs-cordoned-off-over-earthquake-safety-fears

The amount of buildings off limits is going to bring the city to a stand-still.

Yes, and it isn't as though nobody knew this. I mean if Christchurch wasn't a big enough hint. An earthquake closer to Wellington than this will not only destroy the infrastructure but will kill a lot of people. Wellington will be totally isolated, there aren't many roads in or out, the airport will definitely be out of action and probably the port as well. All that realized land is a real hazard too.

 

[StevieTNZ]

https://www.tvnz.co.nz/one-news/new-zealand/strong-magnitude-5-quake-strikes-kaikoura-region

A strong magnitude five earthquake struck the Kaikoura district shortly before 8pm tonight (yesterday evening).

I was walking along the beach front at that time and didn't feel anything. Luckily it seems not much, if any, damage was done by it.

I've yet to go into Wellington and see first hand what the state of the city is like. I know that the ports have been quite damaged compared to damage done by the Seddon earthquakes back in 2013.

 

[Astronuc]

As if Christchurch has had enough http://www.stuff.co.nz/national/86758316/christchurch-shaken-by-severe-earthquake

GeoNet has it at 5.69 Mag - http://www.geonet.org.nz/quakes/region/newzealand/2016p881669

Universal Time November 22 2016, 5:13:34
NZ Daylight Time Tue, Nov 22 2016, 6:13:34 pm
Depth 7 km
Magnitude 5.7
Location 15 km south-east of Culverden
Latitude, Longitude -42.88, 172.99

Canterbury Quake Live describes it as: 7 km north-north-east of Scargill, Canterbury, New Zealand; The distance from central Christchurch is 78.24km.
http://www.canterburyquakelive.co.nz/Browse/?reference=quake.2016p882664

5.7 quake closes Inland Road to Kaikoura for assessment
http://www.stuff.co.nz/national/nz-...closes-Inland-Road-to-Kaikoura-for-assessment

There's already a lot of damage to repair.

 

[StevieTNZ]

The low level of aftershocks following the 7.8 magnitude Kaikoura earthquake is "unusual" according to GNS Science.

https://nz.news.yahoo.com/top-stories/a/33288786/kaikoura-aftershocks-unusual-gns-science/

 

[Astronuc]

Some of the New Zealand sea bed lifted over 19 feet (or ~6 m) during earthquake.
https://www.yahoo.com/news/watch-zealand-sea-bed-lifted-010426406.html

 

[davenn]

Some of the New Zealand sea bed lifted over 19 feet (or ~6 m) during earthquake.
https://www.yahoo.com/news/watch-zealand-sea-bed-lifted-010426406.html

seriously impressive huh

 

[StevieTNZ]

http://www.newshub.co.nz/nznews/ear...ll-retailers-2016112619#.WDk8AK6zmBY.facebook

The cinema and some of the car park at Queensgate mall is to be demolished, which is expected to take 2 - 3 months. Only half of the shops in the mall are open; the area near the cinema cordoned off for safety as they demolish the damaged areas. Sucks because those retailers miss out on customers doing Christmas shopping. I am quite surprised that the said areas need to be demolished in the first place, despite no building being completely earthquake proof. It makes me wonder how well these buildings are built.

I went into Wellington on Friday evening. Noticed cracks here and there on the footpaths and roads. However, the city was quite lively, as one would expect even if no earthquake had occurred, on a Friday evening.

 

[Astronuc]

Geonet published some information on ground acceleration. Several location has about 1 g, with a maximum of about 1.3g. A station in Waiau had an alarming reading of 3g, but apparently it's suspect.

PGA Information (http://info.geonet.org.nz/display/quake/2016/11/16/Shaking+from+Kaikoura+Earthquake)
The strongest ground shaking measured by GeoNet instrumentation so far was a peak ground acceleration of (PGA) 1.3g in Ward. Since publishing this story, data has come in from the WTMC station in Waiau with a vertical PGA over 3g. As yet, we're unsure if this is a reliable value, it may have been contaminated by other effects.

http://info.geonet.org.nz/display/q...preview=/20545678/20545833/PGAmap_M7.8_V4.png

 

[StevieTNZ]

An interesting article about this earthquake -- https://phys.org/news/2018-11-huge-quake-edges-zealand-islands.html

 

[davenn]

An interesting article about this earthquake -- https://phys.org/news/2018-11-huge-quake-edges-zealand-islands.html

thanks :)

 

[davenn]

Some of the New Zealand sea bed lifted over 19 feet (or ~6 m) during earthquake.
https://www.yahoo.com/news/watch-zealand-sea-bed-lifted-010426406.html

I finally got to see this for myself in March 2019 when I did a visit back to NZ. My son and I did a
road trip up to Kaikoura and then further up the coast. Road and rail damage is still being repaired
after the many landslips of the hillsides, slumping of roads and where faults crossed roads.

This is from the north side of the Papatea Fault, looking south. The fault runs along the base of that
that ridge where all the landslips can be seen.

3 images of the coastal section showing the Papatea Fault

looking along strike ... total vertical offset here varies from ~ 1.5 to 2 metres
The vertical offset maxed out at around 2.5 metres. It was the horizontal offset that was
up to 19 metres

everything here that has rain water pools on it, everything on the far side of the uplifted
side of the fault, used to be under water at high tide.

My pic's show that there has been considerable weathering of the fault scarp in the 2.5 years
between when the quakes occurred and when I visited

 

[davenn]

some more pic's

raised beach

3 images showing road restoration. Most of the headlands, like in the photos, had serious landslips
associated with them

cheers
Dave