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Fault

Source: Kate Pedley, University of Canterbury (Published on Temblor)

Source: Nicola Litchfield/GNS Science (Published on the RNZ website)

Fault deformation is the permanent buckling or creasing of the ground surface. Fault deformation can cause significant damage to structures built across or close to a fault.

Introduction

What is fault deformation?

Fault deformation is the permanent buckling or creasing of the ground surface. It is caused by movement on a fault, typically as a result of a fault rupture during an earthquake.

Fault deformation is different to ground shaking from an earthquake. Ground shaking is the vibration of the ground during an earthquake, and it varies depending on the ground conditions and the proximity to the fault rupture. Fault deformation, on the other hand, is the actual cracking and movement of the ground surface itself above the fault.

Fault deformation can cause significant damage to structures built across or close to a fault.

Active faults in Nelson

The Nelson region has a number of faults. Eight faults are identified as active or potentially active, meaning they have ruptured and/or caused ground deformation within the last 125,000 years, or where evidence suggests the fault may be potentially active. These faults are the Flaxmore, Waimea, Eighty-Eight, Jenkins, Whangamoa, Bishopdale, Grampian and Hira faults.

Our understanding keeps improving

What we know about fault hazard in Nelson continues to evolve as new areas are investigated and more detailed studies of known faults are undertaken. Methods used to assess fault hazard have changed over time, especially following the 2010-2011 Christchurch and 2016 Kaikōura earthquakes.

Fault hazard assessments

Since the 1990s Nelson City Council has commissioned studies on the eight active or potentially active faults (described below). These are generally regional scale studies that are not intended to provide detailed information for individual properties. If detailed information about a specific site is required, a qualified professional will need to carry out a site-specific assessment.

The studies are listed below, starting with the oldest to the most recent.

The Fault Hazard Overlay was created using the best information Council had available in the 1990s when the Nelson Resource Management Plan (NRMP) was first developed.

The overlay shows areas where active faults were known or thought to exist at that time. Due to uncertainty of the exact location of the faults, the mapped areas were made wider than would be expected (generally 150 metres wide). This means the mapped overlay is larger than the area that would actually be affected if the fault ruptured.

Report

Assessment of the location and paleoearthquake history Waimea-Flaxmore fault system in the Nelson-Richmond area with recommendations to mitigate the hazard arising from fault rupture of the ground surface - August 2013

In 2013, a study commissioned by Council identified a Fault Hazard Corridor based on updated geotechnical information. This mapped the location of active faults in the Nelson region more accurately than previously.

The 'corridor' is a more refined version of the earlier Fault Hazard Overlay (see above). In areas where there was more certainty about where the fault is located, the mapped area was narrowed down from the original 150 metres wide, which is why it is called a 'corridor'.

The Fault Hazard Corridor has not been incorporated into the Nelson Resource Management Plan (NRMP).

Report

Natural Hazards Fault Rupture update - May 2019

The Fault Hazard Corridor was updated again in 2019. This update used geotechnical information received as part of resource or building consent applications over recent years.

The updated mapping of the Fault Hazard Corridor has not been incorporated into the Nelson Resource Management Plan (NRMP).

Report

Revised Nelson Fault Deformation Overlay - 10 December 2021 - Reissued April 2022

In 2021, Council commissioned a new assessment of faults in Nelson, to update our information and to inform resource management planning.

This report identifies areas around active or potentially active faults within which fault deformation could potentially occur in the event of an earthquake.

These areas are shown as a ‘Fault Deformation Overlay’, which includes three mapped areas:

  • ‘Existing section of fault rupture overlay’ (i.e. areas that remain unchanged from the 2019 revision)
  • ‘Revised section of existing fault rupture corridor’ (i.e. areas revised since the 2019 revision)
  • ‘Less defined section of the overlay’ (i.e. where the location of the fault trace is less certain)

The revised overlay/mapping has been generated at a regional scale (1:5,000 to 1:10,000). It was developed in general accordance with national guidance produced by the Ministry for the Environment (MfE) in 2003.

A wide range of information and data sets were used, including:

  • Previous fault assessments completed for Council
  • Existing resource consent data – including property assessments
  • Field mapping of faults and geology outcrops
  • Hill-shade model and digital elevation models generated from LiDAR
  • Historic aerial photography
  • New Zealand Geotechnical Database
  • Published geological maps

Peer review

Nelson Fault Deformation Overlay - Peer Review - 19 November 2021

Report

Updates to Fault Deformation Overlays as a result of Plan Change 29 - 14 October 2025

The 2021 Revised Fault Deformation Overlay, and associated provisions, were included as part of Plan Change 29 to the Nelson Resource Management Plan (NRMP), to apply in the Residential zone. During the Plan Change 29 process, the community had the opportunity to make submissions, and a hearing was held. As a result, the fault deformation mapping was refined in three specific areas of Nelson: around Nile Street, Enner Glynn and Bayview. These NRMP provisions are now operative (since 2025).

The above-linked 2025 report provided by Nelson City Council’s geotechnical consultant explains these refinements. It should be read in conjunction with the Revised 2021 Fault Deformation Overlay report (further above).

The Revised 2021 Fault Deformation Overlay, along with the 2025 refinements in the three areas mentioned above (Nile Street, Enner Glynn and Bayview), is the most up-to-date fault hazard information Council has for Nelson. This information is used for LIM reports (Land Information Memoranda) across all of Nelson, where relevant.

The natural hazard maps

You can view your property on our interactive Fault Map. This is based on the most recent reports we have (i.e. the 2021 report, with updates as outlined in the 2025 report, both linked above).

Check this map to see the most recent mapping of areas potentially susceptible to fault deformation.

Frequently asked questions

Please note that these FAQs specifically relate to fault rupture hazards. For general FAQs that relate to all hazard types, please see our Natural Hazards Landing Page.

Visit the Fault Map to find out whether the latest information the Council holds indicates your property may be susceptible to an earthquake fault deformation hazard.

Properties affected by the following mapping overlays are considered to be potentially susceptible to fault deformation:

  • Existing section of fault rupture overlay (i.e. areas that remain unchanged from the 2019 revision)
  • Revised section of existing fault rupture overlay (i.e. areas revised since the 2019 revision)
  • Less defined section of overlay (i.e. where the location of the fault trace is less certain)

Please see the explanation of reports above for further detail on each of these areas.

Please note that the studies on which the mapping is based are of regional scale and are indicative only of fault deformation affecting any individual site or property. If detailed information about a specific property is required, a qualified professional will need to carry out a site-specific assessment.

As noted above, the Fault Hazard Overlay was developed in the 1990s and still exists as a planning overlay with associated planning provisions in the Rural, Conservation, and Open Space and Recreation zones in the Nelson Resource Management Plan (NRMP). These provisions continue to apply until the NRMP is updated through a plan change or is replaced by a new resource management plan.

However, if you need resource consent for an activity within the Fault Hazard Overlay, applicants and Council staff would take into account the latest assessment of fault deformation hazard during the consenting process.

The ‘less defined’ sections of the overlay show areas where the fault trace is poorly defined or where there is uncertainty around the specific fault location. These sections typically occur where a fault is deeply buried beneath soil, thick alluvium, or landslides; where no surface expression of the fault can be seen; and/or, where the small-scale geological maps are the only available evidence of the fault’s location. The ‘less defined’ sections are typically wider than the fault rupture overlays due to this uncertainty, and typically range from 150 to 250 metres in width (meaning a fault could occur somewhere within this 150 to 250 metre width).

The Fault Deformation Overlay is produced using data and information available at the time the overlay was produced. The width of the overlay varies depending on the accuracy of the dataset used, the anticipated deformation width, confidence in the location of the fault trace, and the 20 metre set-back recommended in national guidance produced by the Ministry for the Environment (MfE) in 2003. This typically results in Fault Deformation Overlay widths between 20-80 metres (meaning fault deformation could occur somewhere within this 20-80 metre area). In some areas, the location of the fault is more uncertain, and therefore the fault overlay is considered ‘less defined’ and there is a greater width within which a fault rupture could occur.

The natural hazards webmap shows the most recent mapping of fault deformation that the Council holds. This relates to the fault assessment undertaken in 2021, with a subsequent update relating to three specific areas (around Nile Street, Enner Glynn and Bayview) (see the above-linked 2025 report for further detail).

For properties in the Rural, Conservation, and Open Space & Recreation zones in the NRMP, the Fault Hazard Overlay that has been in the NRMP since it became operative in 2004 identifies areas that may be susceptible to fault deformation. In these areas, the Fault Hazard Overlay in the NRMP is based on technical information from the 1990s (see above for further detail).

A (NRMP) plan change (Plan Change 29 from 2023-2025) resulted in a Fault Deformation Overlay and a Fault Awareness Overlay being developed, based on more up to date fault information. These overlays only apply in the Residential Zone because it was within the scope of Plan Change 29. The Rural, Conservation, and Open Space and Recreation zones were out of scope of Plan Change 29, therefore the original Fault Hazard Overlay above continues to apply to these zones.

The most recent mapping of fault deformation that the Council holds is the 2021 Fault Deformation Overlay, together with the updates made in 2025. This covers both rural and residential areas. This most recent mapping is shown on our website and is used to inform LIM notations for fault deformation hazard.

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