Welcome to the Christchurch City liquefaction information viewer
This website presents information about the liquefaction hazard in Christchurch City. Most of this information is not new, it's simply gathered together in one place to make it easier to access. We learned a lot about liquefaction from the Canterbury Earthquakes. But liquefaction doesn’t always occur in the same pattern, so it’s important to understand what could happen in future earthquakes. This information can be important when deciding how to construct buildings and infrastructure, and when planning for future development of the city.
You can browse by clicking on the six tabs across the top of the page:
- About – How liquefaction occurs and its consequences.
- Liquefaction Lab – Experiment with different scenarios to see how these impact liquefaction damage.
- Vulnerability Map – A map showing how liquefaction vulnerability varies across Christchurch.
- Earthquake Maps – Observations from the 2010-2011 Canterbury earthquakes.
- Other Maps – General information about ground conditions across Christchurch.
- Compare Maps – Place any two of these maps side-by-side to use the slider to compare them.
You can select a location by clicking on the map or using the address search box. The + symbol on the map shows the selected location, and the green outline shows the surrounding area with similar ground conditions which has been grouped together for the analysis in the Liquefaction Lab tab.
About liquefaction
Liquefaction is a natural process where earthquake shaking increases the water pressure in the ground in some types of soil, resulting in temporary loss of soil strength. Liquefaction can cause significant damage to land, buildings, infrastructure and the environment, as well as economic and social disruption. Click here for more details about the consequences of liquefaction.
There are three key factors which influence whether liquefaction occurs and how severe the resulting ground damage is:
- Soil condition - Usually only sandy or silty soil can liquefy, and soil that is denser needs stronger shaking before it will liquefy.
- Groundwater - Soil can only liquefy if it is below the groundwater table. Groundwater levels move up and down over time.
- Earthquake shaking - Stronger earthquake shaking causes more of the soil profile to liquefy and causes more severe ground damage.
Liquefaction damage
The map shading shows how the distribution of liquefaction damage varies across the city for each scenario. Lighter purple shading represents a lower likelihood of damage, while darker purple shading represents a higher likelihood of more severe damage.
Soil deposits are naturally variable, so the severity of liquefaction damage will vary across an area. Some properties might have severe liquefaction damage while others nearby have only moderate or even no damage. This means that we can’t predict the damage at a specific address, but we can predict the general distribution of damage across an area.
In the liquefaction laboratory the city is divided into 600 areas with similar ground conditions. These areas are shown with a green outline when you click on the map. The pie chart on the right shows how the estimated liquefaction-induced damage is distributed within that area, with the percentage of the land area predicted to have each of the three degrees of damage. You can see the distribution of liquefaction damage change as you select different earthquake and groundwater scenarios using the sliders above, or click on different areas on the map.
Vulnerability to Liquefaction
Christchurch City Council commissioned Tonkin + Taylor to prepare a liquefaction vulnerability map which follows the most recent national liquefaction guidance. This map is shown to the right, and the full report can be downloaded here. You can browse the key sources of information that were used to develop this updated liquefaction map by clicking on the six tabs across the top of the page.
The map uses the seven categories shown in the table below to describe the vulnerability of the land to liquefaction-induced damage. As well as describing the likelihood and severity of ground damage, the categories also show where there is more or less certainty about the ground conditions. For example, in some areas there is enough information to distinguish between areas of “Medium” and “High” vulnerability. But in other areas where there is less information it might only be possible to conclude that “Liquefaction Damage is Possible”. When more detailed information becomes available in future (e.g. new ground investigations), this might show that the actual vulnerability is “Medium” or “High”, or in some cases perhaps even “Low”.
There was already a substantial amount of previous information available about the liquefaction hazard in Christchurch, and the results of this latest assessment broadly align with what was previously known. This updated map makes improvements to the previous understanding of liquefaction vulnerability by:
- Analysing the extensive collection of ground investigation data now available on the New Zealand Geotechnical Database.
- Using observations of land damage caused by the Canterbury earthquakes to help calibrate predictions of future land damage.
- Drawing on improved scientific understanding for analysis of liquefaction triggering and the resulting consequences.
- Using the improved geology and groundwater maps that are now available, to better define areas of similar land performance.
- Providing coverage of the entire Christchurch City territorial land area.
- Using the consistent framework from the new national guidance to standardise the assessment methodology.
National liquefaction guidance
In 2017 the national “Planning and engineering guidance for potentially liquefaction-prone land” was released. It establishes a process to manage liquefaction-related risk in land use planning and development decision-making. A key objective of the guidance is that buildings and infrastructure are located and built with appropriate consideration of the land conditions.
The guidance encourages consistency in how liquefaction is assessed across New Zealand, to make it easier to transfer knowledge and develop efficient standardised solutions. It recommends that maps are prepared using the seven liquefaction vulnerability categories shown above. For more detail about the performance criteria that are used to determine which category applies, Click here.
