Here is an extensive report on Liquefaction in Canterbury.
“Review of liquefaction hazard information in eastern Canterbury, including Christchurch City and parts of Selwyn, Waimakariri and Hurunui Districts Report No. R12/83″ “GNS Science Consultancy Report 2012/218 September 2012- FINAL December 2012″
Please keep in mind that liquefaction is not determined by silt or ejecta on the surface. These are byproducts of liquefaction. The most severe form of liquefaction is lateral spreading.
My observation after having read this report is that I do not find it acceptable practices to exclude specifically areas that have groundwater higher than a meter. Large areas in Christchurch are affected by this problem and it is conveniently missed in this report. Much of this problem, not all, is caused by the earthquake subsidence.
The highest groundwater reported on in this report is less than 2m.
If a map would be produced for the areas that have water at less than a meter results would be much more severe than this report indicates.
Here below see the areas affected by groundwater at less than a meter. Ground bearing has been lost in many cases. Bearing capacity of wet versus dry sand is about 50% less. Higher groundwater defines increased liquefaction vulnerability. (ILV)
To compare here see groundwater following the September quake 2010.
It is hard to believe that on the maps published the areas that are worst affected have simply been left out. As you can see on the map below where I have combined the groundwater map and liquefaction map. You can clearly see that where the groundwater measures less than a meter from the surface hardly any measurements have been done.
Why are these maps published as a reference for liquefaction and worst affected areas excluded?
It is evident on the groundwater maps (not a part of this report) that crust thinning and loss of land bearing is a result of the earthquakes.
Why are these properties not identified as increased risk of liquefaction?
What is your opinion?