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”
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:
“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.”