Earthquakes & Tsunamis in Christchurch

[Tentun]

Hi everyone
Am really new to this forum and have only just submitted an EOI to immigrate with my family. I've read lots of other threads and they've all been really helpful, thank you.
I know there has been endless talk about the earthquakes in New Zealand but does anyone live in Christchurch and know what the earthquakes are like in that city. It's our first choice city and I notice that it doesn't seem to be on the direct fault line but I guess that doesn't mean it's not suseptible to the effects. And Tsunamis? Someone said to me that Christchurch would be totally underwater if a Tsunami hit? What are the chances of that?
Thanks for your help
Tentun

[Mal]

Christchurch is not on a major fault line, so major quakes are unlikely here, but not impossible. However, small quakes do occur, my workmates reckon a couple of times a year but only small ones. We have been here 7 months and have not felt one yet. As with anywhere in New Zealand I think they are a risk.

As for tsunami, New Zealand is at a fairly equal risk to most places in the Pacific. There some info at http://www.gns.cri.nz/what/earthact/tsunami/index.html

As with all these things, there are many more mundane hazards to your health that you can spend your time worrying about, and that are far more likely to affect you ... crossing the road, sunburn, etc.

[dean1968]

You can always live on the port hills of ch-ch if you are really worried abouty tsunami.
The whole of ch-ch is only a few metres above sea level. They have try to build office buildings with basements to accommodate underground car parking and had to stop due to underground water (stream) flowing through the middle of Christchurch city.

The good news is that people are more aware of tsunamis. In Ch-ch they wanted to tear down the sand dunes that act as a natural barrier and protect from land erosion, they are at least 2 stories or higher in some places that run along the coast ocf Ch-ch. Property developers try to get rid of them because of asethetics, blocking their view of the ocean. This has been quietly forgotten and they would never get resource consent today. There are other factors that ch-ch city have done to minimise the threat. There is a lot of forest, big tracts of land that runs along the coast and they find again that it can minimise the damage from a tsunami as it acts as a natural break.

Return periods are shown for tsunamis, ranging in height to nearly 8 metres, at nine coastal locations around New Zealand. These sites are arranged in order from those where there is a low likelihood to those with the highest likelihood of a tsunami occurring:

Whangarei
Dunedin
Auckland
Tauranga
Timaru
Wellington
Napier
Gisborne
Lyttelton

Whereas, at Lyttelton a one metre high tsunami might occur with a return period of 30 years and a 7.5 metre event every 200 years.

Regarding earthquakes , by a natural fluke many buildings aren't high in ch-ch because of a lot of land. They found in the Mexician earthquake that when buildings sway, they were hitting against each other (too tightly packed together) and were originally designed to do this. The problem was they were built to close to each other.

There is a major faultline but it is further away from Christchurch.

A lot of thought has gone into planning for a disaster. A system designed to make sure Christchurch does not lose drinking water held in reservoirs on the Port Hills to safeguard water in an earthquake in water lines are damaged. Some part of ch-ch are on shingle which means it was an ancient riverbed. Again they aware of 100 year scenario of prone to flooding but they have built stopbanks to minimise the damage.

[Moorf]

We've been here in Canterbury for 2.5 yrs and I've felt one, maybe 2, neither of which were anything more than a vague rumble that sounded more like a heavy truck going past the house.

You'll find that when you buy a house in Chch you may be advised that it is "subject to liquefaction" or words to that effect, in the reports you get. This goes for most of Chch so it can't be avoided (from what I have been told by our solicitor/agents)

Liquefaction, according to Wikipedia.

Being a flat plain I'm not sure Canterbury would be well protected in a tsunami, the pacific warning system should give city dwellers plenty of time to get up the Port Hills (along with the rest of Chch)..... (Sumner residents will probably slip in to some lycra and cycle up the hill or grab their surf boards! )

There's a hill about 15km up the road from us in Springfield that is near the fault line (the Alps is the fault line) - geologists have found it is rising at 6 inches a year!

http://www.stuff.co.nz/search/3900067a6009.html

They say it will rupture - at first stories like this worried us, but you soon realise it's a common thread and once in a while they pop out another "NZ is gonna blow" story... as far as the locals are concerned, they know it's there and just get on with it

[willsken]

We felt one here the other day. The neighbours said it was a big one and the boys and OH felt it. No idea where I was at the time... I didn't feel a thing!

[westi]

We've been here since the begining of Dec and haven't felt the earth move yet ( ! )
We're in the process of buying a house and were told by the lawyer that Christchurch is built on a marsh so if there was a big earth quake it would turn to jelly.... but hey !

[StevieD]

Know the feeling westi!!

[Moorf]

built on a marsh so if there was a big earth quake it would turn to jelly.... but hey !

... that's liquefaction..

[Trigirl]

They say it will rupture - at first stories like this worried us, but you soon realise it's a common thread and once in a while they pop out another "NZ is gonna blow" story... as far as the locals are concerned, they know it's there and just get on with it

this is so the right attitude

*but* if you aren't going to be able to manage the kiwi laid back attitude to earthquakes then NZ may not really be the place for you. when the south island alpine fault goes (50% chance of it being in the next 20 years according to the latest research) it'll pretty much certainly cause serious damage in christchurch - but perhaps not on quite the devastating scale that it will on the west coast.

[wiki]

If you really want to scare yourself this site has all recorded/reported earthquakes in NZ with a location scatter map - http://www.geonet.org.nz/recent_quakes.html

I lived in Te Anau for eight years (on the fault line) and we got one noticable quake a year that did little more than knock groceries off supermarket shelves.

The last time there was a fatal earthquake in NZ was 1968 I think, near Reefton on the West Coast of the SI. Only three or four people died, but then again the population is pretty small over there. More than 250 people died when a quake hit Napier/Hastings in 1931 - but on the bright side, it did mean that Napier had to be almost totally rebuilt which is why it now has such a complete art-deco feel.

So many NZ cities are on coastal planes or around inlets so the risk of tsunami is always there. The best you can do is be prepared, or move to a more stable country.

As Trigirl said, most NZers are pretty laid back about the earthquake risk - very much a case of "if it happens, it happens"