Day of reckoning approaching: scientists warn New Zealand’s Alpine fault about d

[Mark]

June 28, 2012 – NEW ZEALAND – GNS Science and University of Nevada-Reno scientists have found that the southern part of the 800 kilometre-long fault which runs along the western edge of the Southern Alps from Marlborough to Milford Sound causes quakes of around magnitude 8 every 330 years on average. Dating leaves and seeds from a river terrace at Hokuri Creek near Lake McKerrow in far northwestern Southland, just north of Milford Sound, revealed 24 Alpine Fault quakes between 6000BC and the present. Other research has found the most recent was in 1717, meaning the next may be only 30 or 40 years away, based on averages. Professor Richard Norris, from the geology department at Otago University, said the Alpine Fault had the highest level of probability for rupture of any fault in New Zealand. “Westland obviously is at high risk, with widespread damage likely and roads, bridges and other transport links likely to be badly affected (as well as the tourist trade),” he said. The fault crossed the main West Coast road in many places, and with an estimated 8m displacement would completely destroy it. “Intensities further east in places like Queenstown, Te Anau, Wanaka and Mt Cook will be high enough to cause landslips and do damage,” Norris said. “Further east in the major cities of Christchurch and Dunedin, the intensities will be lower but the duration of shaking could still be sufficient to damage poorly constructed buildings…and possibly cause some liquefaction.” Places such as Nelson, Wellington and Invercargill could also expect to feel some shaking. Project leader Kelvin Berryman of GNS Science said “a major earthquake in the near future would not be a surprise. Equally it could be up to 100 years away. The bottom line is, if not in our lifetimes then increasingly likely in our children’s or our grandchildren’s.” The study’s findings, published today in the journal Science, were new and internationally significant, Berryman said. Auckland University biostatics professor Thomas Lumley said the intervals between quakes on the Alpine Fault tended to be quite close to the average interval, with relatively little spread.  –Stuff

• Tweet

[Sara]

With all the activity in NZ at the moment, maybe it will be sooner than later. Just imagine the damage in built up areas and the cost to Nzer's. Hopefully there will be no fatalities, but at that magnitude there propbably will be. Lets keep our finger crossed, it might be tomorrow.

[Weather Display]

sounds like alot of work has been done to get these conclusions
and hopefully people take heed...
will stuff transport by the looks, thats for sure...will be alot of spilt milk from dairy farms for starters

[Deano]

There was a Cambell article after 3 News last night. Great shots of the sediment layers going back so many years. GNS have been busy.

[Mark]

I did see that to Deano great story.
It will happen and it and the effects will be worse than we think.

[OhauitiWeather]

Would really like to take a look at that program/item.  Can anyone post a link to that item or program, or even some more information on it so I can serach for it online.  Thanks.

[Deano]

Here we are David. After the DotCom piece. 6:50 in
http://ondemand.tv3.co.nz/Campbell-Live-Thursday-June-28-2012/tabid/119/articleID/7073/MCat/73/Default.aspx

[JennyLeez]

There is quite a bit here also David

http://www.gns.cri.nz/Home/News-and-Events/Media-Releases/improved-understanding-of-alpine-fault

[hotcop65]

And on a lighter note............. living in Tokoroa is not a bad thing then, no rocking and rolling here

[OhauitiWeather]

http://ondemand.tv3.co.nz/Campbell-Live-Thursday-June-28-2012/tabid/119/articleID/7073/MCat/73/Default.aspx[/url]

Very good segment, thank you very much for posting the link to the Video. Much appreciated.

[Suezy]

Thank you Mark for starting this  and it is very informative.  My eyes are  still no good and not up to cutting and pasting as yet and note that there iss very little mention of as to how the West Coast would fare out of this. The Councils over there have been kept fully informed and kept regularly updated from what I hear.  They would be very badly affected unfortunately and wondered if you could find more on this and paste here.
Not a very joyous thing to live with down here but as they say we would only get a mag 5.8 or so but the continuing of the shaking would do the damage.  Being so close to the Greendale fault line and the 7.1 was bad enough with the length of time that that went on for let alone with one going on for the length of over 600 km or so plus the psygur? trench.
Keep up the good work and certainly miss being able to post here - thanks again MArk.

[Mark]

Nice to hear from you Suezy.
I shall keep my eyes out for more info for you.

[Deano]

I was browsing the GeoNet website after these posts and am wondering why there are no deep quakes shown on the Alpine Fault for the last 10 yrs.

Does it seem strange?
Plenty on the shallow map.
Or is the pressure building...

[TokWW]

Yes, good find - that does look worrisome doesn't it!  I wonder what the longer term history is - when was the last M6+ earthquake along that section?

[Deano]

Upon searching some more, I came across this article from Gns.
"In between earthquakes, the Alpine Fault is locked. All these things mean that the Alpine Fault is a globally significant geological structure. "
Horizontal movement of the Alpine Fault is about 30m per 1000 years — very fast by global standards. Each time it has ruptured, it has also moved vertically, lifting the Southern Alps in the process. In the last 12 million years the Southern Alps have been uplifted by an amazing 20 kilometres, and it is only the fast pace of erosion that has kept their highest point below 4000 metres.
Rest of the story here. http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Major-Faults-in-New-Zealand/Alpine-Fault

[Weather Display]

I dont think its problem no deep earthquakes on the alpine fault zone....its obiously not a fault line that produces deep earthquakes....umlike the north island volcanic type (subduction type), which produces deep earthquakes

[David]

Yes you are right Brian - there are no deep quakes along the Alpine fault because it is not a subduction zone. Deep quakes north of the fault are on the northern subduction zone, deep quakes in Fiordland southwards are on the southern subduction zone which includes Puysegur Trench

[TokWW]

This map here from USGS shows a distinct lack of major earthquakes in this region greater than M5.5.

[einzack]

one of the reason the alpine fault looks different in that picture is the mechanism of movement also changes.
the alpine fault is predominantky strike-slip, which means it's moves laterally, but with relatively little vertical movement. the sections of the plate boundary to the north and south of the alpine fault are subductions zones, where all the movement is predominantly in the vertical plane.
because the alpine fault is strike slip, this helps explain the lack of deep earthquakes along it.

here's a better way of explaining it that what I did:
Between the two zones of deep earthquakes, there is a gap in deep earthquake activity which coincides with the Alpine Fault.  This marks the boudary between the Pacific and Australian plates where the two plates push past each other sideways, rather than one plate diving under the other.  They are also pushing together with such force that the Southern Alps are squeezed up along the seam.  The sideways movement means that parts of Nelson and west Otago that were adjacent to one another five million years ago are now 450 km apart, and that in another 10 million years, Haast on the Australian Plate and Christchurch on the Pacific Plate will be close neighbours.

The lack of deep earthquakes along the Alpine Fault zone is because neither plate is diving below the other.  The rocks on both sides of the boudary are too bouyant, and when there is no cold, rigid plate edge descending to great depths, there are no earthquakes generated along the interface.

list of the large alpine fault earthquakes:
    1848 - Marlborough, estimated magnitude = 7.5 (12km)
    1888 - North Canterbury, estimated magnitude = 7.3 (12km)
    1929 - Arthur's Pass, estimated magnitude = 7.1 (11km)
    1929 - Murchison, estimated magnitude = 7.8 (20km)
    1968 - Inangahua, estimated magnitude = 7.1 (12km)
    2003 - Fiordland, estimated magnitude = 7.1 (24km)
    2009 - Fiordland, estimated magnitude = 7.8  (12km)


edit: ah, i see I was beaten to the punch