Big Alpine Fault rupture due in the next century or two

The Alpine Fault is a big feature of South Island geography and seismic activity. It last ruptured in 1717 and there is a big earthquake, on average, about every 300 years, but the times vary so there is thought to be about a 30% risk of the next ‘Big One’ in the next fifty years.

When I was woken up by an earthquake in the middle of the night on 4 September 2010 I wondered if it was ‘the big one’ – it was big enough but that was centred close to Christchurch.

This image clearly shows the fault running up the West Coast, where the Australian plate dives under and drives up the Southern Alps which line along the rising edge of the Pacific Plate.

Project AF8 have been preparing for a severe earthquake on the Alpine Fault for two years.

Stuff has the latest information on this: Videos show devastating impact across South Island if Alpine Fault ruptures

Video simulations demonstrate widespread destruction across the South Island if New Zealand’s most dangerous fault line ruptures, and there’s evidence the country is due for another big one.

Project Alpine Fault Magnitude 8 (AF8) released a series of videos on Wednesday, warning there’s compelling geological evidence to show it produces a significant earthquake of magnitude eight or greater every 300 years on average.

The last rupture was believed to have happened in 1717.

That sounds dramatically imminent, but the intervals have actually varied between 140 and 510 years, so it may or may not happen in our lifetimes.

The Stuff has the latest videos.

Extensive details are at Project Alpine Fault 8

The Alpine Fault is the biggest but just one of many fault lines affecting New Zealand. This is a few years old but is a good look at plate tectonics in New Zealand:

Dunedin is about as far as you can get in the South Island from the fault but when the big one strikes it is certain to be felt here (we feel larger Fiordland earthquakes as well as the bigger Christchurch quakes) and it is likely to have  major effects across the South Island, and also in the lower North Island.

South Island flooding effects

A satellite photo of the South Island following the heavy rain and floods shows all the sediment washing out to sea:

CawthronSouthIslandFloods

Zoomed in to show the Taieri Plain flooding (just to the left of ‘Dunedin’, with the sediment outflow at Taieri Mouth washing up the coast.

CawthronTaieriFlooding

I went down the coast to Taieri Mouth on Sunday, the river looked like a swollen sludge outflow. The surf right down the coastline was very dirty.

The sediment from the Taieri River is drifting up the coast towards Dunedin.The Taieri River comes from the Maniototo where there was also heavy rain.

The sediment outflow in the bottom right of the photo is from the Clutha River. There was also flooding upriver there.

From:

CawthronSouthIsland.jpg

From the CawthronEye Satellite.

 

South Island from 330 km-ish

The International Space Station orbits at a mean altitude ranging of 330 (it needs periodic boosts to restore it’s altitude).

Here is a photo of the South Island of New Zealand posted on Twitter by @Thom_astro:

dap5_37xsaac41g

Thomas Parquet:

Européen Français, pilote de vaisseau spatial à l’ESA en mission pour six mois sur l’ISS / Euro-French spacecraft pilot at ESA, now on 6-month ISS mission

More interesting pics of different parts of the planet from him  here.

 

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.

Today’s big news – snow on a skifield

I haven’t watched television news for over a week until getting home today. I’ve watched the headlines on both Prime and 3 News.

Apparently one of the big news story’s of the day is there is some snow on a mountain skifield.

They both showed Coronet Peak without saying if this extraordinary phenomenon had occurred on  other mountains or not.

It did – I saw quite a few snow capped ranges this afternoon as we flew across the South Island. I’d say the snow line is above 1,000 metres so it’s still confined to the tops of the hills.

Sure there’s a bit of a nip in the air – we landed to 4 degrees – but that’s not particularly unusual in a southerly change here.

The forecast is for snow tonight – what will they put on the news if there’s actually snow at altitudes that people live?

It just seems a bit desperate to go up to a ski field to find some snow for a weather story.