The online tool – the Liquefaction Lab – uses the extensive information about ground conditions gathered since the 2010-11 Canterbury earthquakes to visualise an area’s vulnerability to liquefaction under different conditions.
The Liquefaction Lab shows different patterns of land damage that are likely to occur across the city by taking into account the magnitude and location of the earthquake and groundwater levels.
“We have taken all the observations about how the land has performed in previous earthquakes and brought these together with the extensive data and research gathered since then to map the liquefaction vulnerability of all the flat land in Christchurch,” Christchurch City Council Head of Strategic Policy Emma Davis says.
The mapping includes new vulnerability categories that will eventually replace the TC1, 2 and 3 categories introduced in Christchurch after the earthquakes, as the Ministry of Business, Innovation and Employment (MBIE) introduces the new categories nationwide by next year.
Liquefaction is a natural process where earthquake shaking increases the water pressure in the ground causing some soils to behave like a fluid, resulting in temporary loss of soil strength.
Liquefaction can cause significant damage to land, buildings and infrastructure, through sediment being ejected to the ground surface, and subsequent ground settlement, ground cracking and lateral spreading.
The amount and nature of liquefaction ground damage that occurs in an earthquake depends on the soil type, the strength of earthquake shaking and groundwater level at the time.
Christchurch is very familiar with liquefaction, with parts of the city experiencing significant liquefaction as a result of the 2010/2011 Canterbury Earthquakes. Following the earthquakes, a lot of information has been collected about the city’s ground conditions.
From this, Christchurch City Council have mapped the liquefaction vulnerability of all the flat land in Christchurch District, (not including Kaitoreke Spit and Banks Peninsula). This allows you to explore how the soils, magnitude and location of an earthquake and groundwater levels can affect likely patterns of land damage.
This understanding of the liquefaction hazard across Christchurch helps the Council make informed decisions about future land use and the building controls required to manage risk.
The assessment (report [PDF, 10 MB] + appendices [PDF, 25 MB]) includes new vulnerability categories that will replace the TC1, 2, 3 technical categories introduced in Christchurch by MBIE after the earthquakes. The new categories will be introduced nationwide in 2021.