Liquefaction is a well known natural process in Christchurch following the 2010/2011 Canterbury earthquakes. Understanding liquefaction vulnerability helps guide decisions about future land use and designing infrastructure and homes to manage risk.
Liquefaction
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.
Liquefaction in Christchurch
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, we have mapped the liquefaction vulnerability(external link) 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.