Liquefaction In Christchurch

ECAN document

We’ve found a very useful Environment Canterbury document “Solid Facts on Liquefaction in Christchurch

It details areas of Christchurch that have high, moderate and low liquefaction potential, explains what liquefaction is, how it is caused and the effects it has.

We think it may have been written before the 4 September Quake because it seems to concentrate mostly on the rupture of the Alpine Fault, but it has a publication date of 7 September 2010.

The Alpine Fault is only one of around 100 sources of earthquakes for Canterbury, some of which are capable of producing liquefaction in Christchurch. The Alpine fault has the potential to produce a magnitude 8 earthquake

New Zealand is on the boundary of two of the earth’s plates, the Australian Plate to the west and the Pacific Plate to the east.

These plates are moving against each other and, because of this, New Zealand is a highly-active earthquake zone.

The earthquake hazard is even more extreme for Canterbury because of the Alpine Fault. It is the “on-land” boundary of the Australian and Pacific Plates, and is New Zealand’s largest active fault, running under the Southern Alps for over 500km.

The Alpine Fault can produce magnitude 8 earthquakes and does so about every 300 to 350 years. The last earthquake on the Alpine Fault was in 1717.

Ground shaking intensities in Christchurch during an Alpine Fault earthquake will be high enough to cause liquefaction. The Alpine Fault is not the only source of earthquakes for Canterbury, with about one hundred other sources having been identified. Some of these are also capable of producing strong ground shaking and liquefaction in Christchurch”

More here

An account of the quake by a resident in Kingsford Street was published on Stuff.  She tells of dozens of geysers spewing out water as the earthquake liquified the ground:

Kate

“As soon as we woke, there was no doubt that this was a massive earthquake. Every time we moved to the north, our house tilted forwards, and wouldn’t recover as we moved back to the south. We assumed that we were falling off our piles (we later discovered that the whole house was sinking into the earth due to the liquefaction).

When the shaking, rumbling and rattling ended, we were horrified to hear a loud gushing and gurgling of water – as if a river had been diverted through our property. We rushed to turn off the hot-water cylinder, thinking it had sprung a leak, but the sound didn’t go away.

When we peered out the window (the power and street lights were off) we saw dozens of geysers spewing out fountains of water.

We hauled on clothes (not easy when you’re shaking like a leaf), grabbed the trusty dynamo torch from beside the bed, and tried to get outside to check on our neighbours. The front and back doors were jammed shut, but we managed to escape through the conservatory. We waded our way along the neighbour’s driveway, which was ankle deep in mud and water.

We enjoyed a nice cup of tea, boiled on a gas stove, with the neighbours while we waited for sunrise.

The workmen have been absolute legends – working their butts off while their own homes and families needed attention. We are incredibly grateful!

Now we are waiting to hear whether our homes can be saved, or whether our land will be declared unfit to be built upon.”

 

 

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6 thoughts on “Liquefaction In Christchurch

  1. Does anyone know of a printer freindly versionj of the “Solid Facts” pdf?
    All that black ink is a killer!!

  2. This is not unusual. There are extensive maps of liquefaction, tsunami, landslide and ground shaking risk on the Wellington City Council website: http://www.gw.govt.nz/assets/Emergencies–Hazards/combined_earthquake_hazard_map_wellington.pdf

    The whole of New Zealand is prone to natural disasters, including earthquakes, volcanoes and tsunami. It’s part of every home buyers’ responsibility to do their due diligence w.r.t. the risk of their property.

    NZ is very fortunate to have such a comprehensive insurance system as the EQC in operation, but if any of us are affected by a natural disaster, we must expect to pick up the tabs for loss of equity and out-of-pocket costs ourselves.

  3. I also have a copy of this map, it was given to me by the previous owner owner of our house nearly five years ago along with a map of where the old Waimak used to flow and yes branches of it flowed through Christchurch and Kaiapoi. I believe, looking at the map that the river still flows underground through it’s old route and is popping up as springs feeding the likes of the Avon, the groynes etc. It’s interesting to note that this route has a close resemblance the the map you have shown. My father was a bulldozer operator back in the 50’s 60’s and he remembers bulldozing Kingsford Street in Christchurch. This street is a disaster. He said he couldn’t believe they built there because when they dug to put the drains in it was like runny sand and they spend a lot of time draining it before bring in truck loads of shingle. Someone told me that someone in the council at the time advised against building there at the time, but they went ahead anyway.

    • I am from Kingsford Street and I totally agree with your “runny sand” comment. We’ve just had our drain pipes repaired. The contractors dug 6-7 feet down to replace the broken pipes but said they could not compact the ground very well afterward as it was mostly sloppy sand! 80% of our property was affected by liquefaction!

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