Do you live in an earthquake prone region in NZ?

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#547206 19-Nov-2011 12:43

IlDuce: When I was at University (Of Canterbury) 13 years ago, we were told Christchurch would be hit by a major earthquake within 30 years. Guess that lecturer was right on the money. He also added for example, the Blenheim Road over bridge would collapse in such an earthquake (anyone remember what year they removed it out of interest?).

My father and I were looking at the struts under the Moorhouse Ave over bridge around Easter and the amount of concrete that cracked and flaked away is pretty scary. It appears to have been within a whisker of complete structural failure.

I've been lead to believe that the struts supporting the motorway in Wellington have steel surrounds to contain the concrete, but this was never implemented on Moorhouse Ave.

catjones

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#547386 20-Nov-2011 11:17

alasta:
IlDuce: When I was at University (Of Canterbury) 13 years ago, we were told Christchurch would be hit by a major earthquake within 30 years. Guess that lecturer was right on the money. He also added for example, the Blenheim Road over bridge would collapse in such an earthquake (anyone remember what year they removed it out of interest?).

My father and I were looking at the struts under the Moorhouse Ave over bridge around Easter and the amount of concrete that cracked and flaked away is pretty scary. It appears to have been within a whisker of complete structural failure. ?

?

I've been lead to believe that the struts supporting the motorway in Wellington have steel surrounds to contain the concrete, but this was never implemented on Moorhouse Ave.?

You can see the metal bars in it. I think they call this reinforced concrete?

alasta

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#547396 20-Nov-2011 11:46

catjones:
alasta: My father and I were looking at the struts under the Moorhouse Ave over bridge around Easter and the amount of concrete that cracked and flaked away is pretty scary. It appears to have been within a whisker of complete structural failure.

I've been lead to believe that the struts supporting the motorway in Wellington have steel surrounds to contain the concrete, but this was never implemented on Moorhouse Ave.?

You can see the metal bars in it. I think they call this reinforced concrete?

Yes, there is internal reinforcing (thank god) but no external surround.

nickb800

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#547419 20-Nov-2011 13:01

alasta:
IlDuce: When I was at University (Of Canterbury) 13 years ago, we were told Christchurch would be hit by a major earthquake within 30 years. Guess that lecturer was right on the money. He also added for example, the Blenheim Road over bridge would collapse in such an earthquake (anyone remember what year they removed it out of interest?).

My father and I were looking at the struts under the Moorhouse Ave over bridge around Easter and the amount of concrete that cracked and flaked away is pretty scary. It appears to have been within a whisker of complete structural failure.

I've been lead to believe that the struts supporting the motorway in Wellington have steel surrounds to contain the concrete, but this was never implemented on Moorhouse Ave.

Much more neccesary in wgtn as a collapse of the urban motorway at Thorndon would cover the main road & rail entrances, prevent access to the main ro/ro ferry terminals, potentially sever underground services - power, tcoms, gas, petrol. Christchurch was lucky in that it doesnt have so much critical infrastructure concentrated into narrow, vulnerable corridors. Plus there is a major fault running right through the middle of it. Gee wellington does seem a bit screwed!

I suspect the OP is looking at this assuming that ALL of chch is a bombsite, which is simply not true, pulling a number out of thin air i would say over 80% of the infrastructure across the city is intact or requiring only minor repair. If you were to 'move' the whole city to say Waikato (ignoring volcanic risk...) then i suspect the cost incurred would vastly exceed the benefits - both avoided quake damage and lost lives at ~$3 million value per statistical life (the value used by NZTA when deciding whether to do safety improvements on roads). A dud policy, basically.

keewee01

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#547432 20-Nov-2011 13:50

catjones: There are regions in New Zealand which are relatively safe from Earthquakes. New Zealand is not Japan. Much of the North Island and the southern part of the South Island are quite safe from strong quakes.

http://en.wikipedia.org/wiki/Earthquakes_in_New_Zealand

I was watching BBC Hardtalk when the presenter asked John Key a somewhat similar question. Why rebuild Christchurch instead of moving it to a much safer place? Why tempt fate?

Just because a map shows an area getting zero earthquakes per year, that doesn't mean that they don't feel the effects of a big quake.

No where in New Zealand could be tagged as being safe of ever suffering an serious earthquake or damage from a major quake. It is the nature of the land we live on.

Edited to fix grammar.

TheUngeek

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#547479 20-Nov-2011 16:51

If the southern alpine faults goes in a big way (which is when not if) Pretty much all infrastructure in the SI is considered to be FUBAR. As in all bridges, slips etc etc. If that happens, I expect to be living off the land for several months.

mattwnz

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#547483 20-Nov-2011 17:03

sbiddle:
nakedmolerat: prior to september last year, christchurch is considered as a low risk area for earthquake..

No it wasn't.

The risk calculations were not as high as Wellington where the calculated return period for a significant quake was considered greater, but Chistchurch was certainly a high risk area, with many detailed plans detailing modelling plans showing exactly what would occur in terms of liquefaction etc.

It wasn"t low risk, but it was considered a lower risk, at least by people in power. This is shown by the building code maps of NZ. No doubt these will now be changed. However as shown by the documentary made in the 90's, chch did have significant risk, due to the ground conditions.

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LennonNZ

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#547493 20-Nov-2011 17:23

So we move the Capital back to Auckland? Or Maybe Russell where it was originally?

Kaos36

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#548088 21-Nov-2011 20:55

The whole of NZ is on one big fault line isn't it, goes right through the center of both islands.

keewee01

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#548129 21-Nov-2011 22:25

Kaos36: The whole of NZ is on one big fault line isn't it, goes right through the center of both islands.

Not quite - South Island, yes - the Alpine Fault... runs off out to sea around Kaikoura and then up of the East Coast of the North Island.

North Island - Wellington Fault, Wairarapa Fault and various others, but none are plate boundaries like the Alpine Fault.

tdgeek

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#548162 21-Nov-2011 23:29

They say when the Alpine Fault ruptures, it will be an 8.0 to 8.5, giving us in ChCh a 7.0 to 7.5.

The PGC and CTV were building failures which should not have occured. Discount the many CBD very old brick based structures that were destroyed or are now being demolished, and we would then have what I feel will have been a city that wouod have weathered the Feb 6.3 well. The buildings will have remained in one piece, doing the one job the building codes require. Allow people to get out. Whether said buildings are usable or not after that is not relevant.

So, here, when the remaining buildings are left, we will have a city that can deal with a big earthquake, as well as one can hope. The concern has to be Welly. I know if I was to wander around there now, I'd have my own opinion on what I would expect to stay up. Sadly, in ChCh, we can see what can and won't.

Positively, the Feb quake was very very large in terms of ground acceleration effect, so if we didnt have 2 poorly designed or strengthened buildings, and many old brick ones, we would have been happy wth how it handled it. A typical high strength quake I think is around 0.8g, Feb 22 was 2.2g in the CBD, caused I think by reflection through the volcanic rock.

So Welly, deal with those 1600 buildings that need it, as time goes by, we all relax, forget the pain, and think too much about the money

mattwnz

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#548163 21-Nov-2011 23:37

tdgeek: They say when the Alpine Fault ruptures, it will be an 8.0 to 8.5, giving us in ChCh a 7.0 to 7.5.

The PGC and CTV were building failures which should not have occured. Discount the many CBD very old brick based structures that were destroyed or are now being demolished, and we would then have what I feel will have been a city that wouod have weathered the Feb 6.3 well. The buildings will have remained in one piece, doing the one job the building codes require. Allow people to get out. Whether said buildings are usable or not after that is not relevant.

So, here, when the remaining buildings are left, we will have a city that can deal with a big earthquake, as well as one can hope. The concern has to be Welly. I know if I was to wander around there now, I'd have my own opinion on what I would expect to stay up. Sadly, in ChCh, we can see what can and won't.

Positively, the Feb quake was very very large in terms of ground acceleration effect, so if we didnt have 2 poorly designed or strengthened buildings, and many old brick ones, we would have been happy wth how it handled it. A typical high strength quake I think is around 0.8g, Feb 22 was 2.2g in the CBD, caused I think by reflection through the volcanic rock.

So Welly, deal with those 1600 buildings that need it, as time goes by, we all relax, forget the pain, and think too much about the money

A lot of wellington buildings have been strengthened to some extent, as it was always seen as the high risk area. But a lot of it doesn't have the same ground conditions as chch, which does amplify the forces. Downtown welly, areas around the sea and reclaimed areas are the place that could be affected the worst.

keewee01

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#548210 22-Nov-2011 08:24

mattwnz:
tdgeek: They say when the Alpine Fault ruptures, it will be an 8.0 to 8.5, giving us in ChCh a 7.0 to 7.5.

The PGC and CTV were building failures which should not have occured. Discount the many CBD very old brick based structures that were destroyed or are now being demolished, and we would then have what I feel will have been a city that wouod have weathered the Feb 6.3 well. The buildings will have remained in one piece, doing the one job the building codes require. Allow people to get out. Whether said buildings are usable or not after that is not relevant.

So, here, when the remaining buildings are left, we will have a city that can deal with a big earthquake, as well as one can hope. The concern has to be Welly. I know if I was to wander around there now, I'd have my own opinion on what I would expect to stay up. Sadly, in ChCh, we can see what can and won't.

Positively, the Feb quake was very very large in terms of ground acceleration effect, so if we didnt have 2 poorly designed or strengthened buildings, and many old brick ones, we would have been happy wth how it handled it. A typical high strength quake I think is around 0.8g, Feb 22 was 2.2g in the CBD, caused I think by reflection through the volcanic rock.

So Welly, deal with those 1600 buildings that need it, as time goes by, we all relax, forget the pain, and think too much about the money

A lot of wellington buildings have been strengthened to some extent, as it was always seen as the high risk area. But a lot of it doesn't have the same ground conditions as chch, which does amplify the forces. Downtown welly, areas around the sea and reclaimed areas are the place that could be affected the worst.

There is still a lot of buildings in Wellington that haven't been strengthened, but at least the WCC is proactive about that.

Wellington could be ground zero for a large earthquake... that will certainly have an impact!

YadaMe

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#548253 22-Nov-2011 09:23

Engineers here in CHCH are saying the measured ground acceleration for the Feb earthquake is the highest measured in an urban area, and the forces were more up/down than side to side. So even though the Magnitude was not that high, the force and direction exerted on the buildings etc was very different to a "normal earthquake".

BurningBeard

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#548263 22-Nov-2011 09:38

YadaMe: Engineers here in CHCH are saying the measured ground acceleration for the Feb earthquake is the highest measured in an urban area, and the forces were more up/down than side to side. So even though the Magnitude was not that high, the force and direction exerted on the buildings etc was very different to a "normal earthquake".

Scary stuff. I was in the office when it happened but a rep I work with was on the road and says he saw cars leave the ground.

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