Liquefaction
A phenomenon where saturated, loose soil loses its strength during an earthquake and behaves like a liquid, causing the ground to shift, sink, or eject sand and water.
What is a Liquefaction?
Liquefaction occurs when waterlogged, loosely packed soil is shaken by an earthquake. The shaking causes the soil particles to lose contact with each other, and the ground temporarily behaves like a thick liquid. This can cause buildings to sink, tilt, or shift, and often results in sand and water (sand boils) erupting through the surface.
The Canterbury earthquakes of 2010-2011 brought liquefaction into sharp focus for New Zealand property buyers. Large areas of Christchurch experienced severe liquefaction, causing billions of dollars in damage and rendering thousands of properties uninhabitable. Suburbs like Bexley, Dallington, and parts of the CBD were among the worst affected.
Liquefaction risk is highest in areas with sandy or silty soils and a high water table — typically near rivers, estuaries, coastlines, and reclaimed land. Many New Zealand cities, including Christchurch, Wellington, Napier, and parts of Auckland, have areas with significant liquefaction susceptibility.
Why It Matters for Due Diligence
Liquefaction risk can affect insurance availability, building costs (foundations may need to be engineered for liquefaction-prone land), and long-term property value. Post-Canterbury, insurers and banks pay close attention to liquefaction risk.
Check the LIM report and regional council hazard maps for liquefaction susceptibility. If the property is in a liquefaction-prone area, consider getting a geotechnical assessment to understand the specific risk and any foundation requirements for future building work.
How to Check
The LIM report may note liquefaction susceptibility. Regional councils publish liquefaction hazard maps — check your council's GIS portal. The GNS Science website also provides liquefaction susceptibility data. For specific properties, a geotechnical engineer can assess the soil conditions and provide a detailed risk assessment.
Frequently Asked Questions
Can you build on land that's prone to liquefaction?
Yes, but it costs more. Engineering solutions like reinforced foundations, ground improvement, or raft foundations can mitigate liquefaction risk. These add to construction costs but are standard practice in areas like Christchurch. A geotechnical engineer can advise on the right approach.
Does liquefaction risk affect my insurance?
It can. After the Canterbury earthquakes, insurers became more cautious about liquefaction-prone areas. You may face higher premiums, higher excesses, or limitations on natural disaster cover. EQC (now part of the Natural Hazards Commission) covers the first $300,000 of residential dwelling damage from natural disasters.
Related Terms
Fault Line
GlossaryA geological fracture in the earth's crust where two tectonic plates or rock masses meet, and where earthquakes are most likely to occur.
Earthquake-Prone Building
GlossaryA building assessed as having structural performance below 34% of the New Building Standard (NBS) for earthquake resistance, making it legally earthquake-prone under the Building Act 2004.
New Building Standard (NBS)
GlossaryA percentage rating that expresses an existing building's earthquake strength relative to the minimum standard required for a new building — 100% NBS means the building meets the current code for a new build.
LIM Report
GlossaryA Land Information Memorandum — an official council report summarising everything the council knows about a property.
Land Instability
GlossaryThe risk of ground movement including landslides, slope failure, subsidence, and land slippage that can damage buildings and infrastructure.
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