Fault line mapping

The Taupō District is particularly vulnerable to seismic, geothermal and volcanic activity. As a result, it has many fault lines running through it, especially to the north-east and southern ends of Lake Taupō. These are areas where the ground has the potential to rupture due to earthquakes. They represent a potential hazard to building and development, in addition to general earthquake shaking which is a risk everywhere.

The Resource Management Act 1991 requires all councils to prepare a District Plan and review the different parts of that plan at least every 10 years. The District Plan manages what people can do on their land and how it can be developed, and part of the review includes looking at natural hazard maps and provisions – and that includes mapping fault lines.

We are currently reviewing the fault line maps in the Taupō District Plan from the 1990s and are updating them.

We contracted GNS Science -Te Pū Ao as technical experts in this area to provide updated fault line maps in August 2020 next District Plan which is currently being reviewed. GNS Science is a New Zealand Crown Research Institute, is owned by the government and operates the national geological hazards monitoring network and the New Zealand active fault database, and it is contracted by numerous other councils to provide scientific advice and information.

A Fault Awareness Area highlights that an active fault is known, or suspected, to be present, but existing mapping is not accurate enough to be sure of its exact location. GNS Science recommends that more work be undertaken before any future new significant building and development in these areas (such as schools, power stations, or new multi-lot housing developments) to identify the location of the actual fault to reduce the risk from a low-likelihood but potentially significant earthquake event.

A Fault Avoidance Zone is a 20 metre buffer zone either side of the identified or suspected active fault. GNS Science recommends that these areas are avoided for new buildings and development in future, or the actual risk posed by the fault line be determined by further site investigation, to reduce the risk from a low-likelihood but potentially damaging earthquake event.

We cannot know the risk of a major event relating to specific individual fault lines or properties with certainty. Generally, we are talking about the risk associated with a low-likelihood but potentially damaging earthquake event. The GNS Science report identifies that the recurrence interval is the time interval between large ground-surface rupturing earthquakes and provides an indication of the likelihood of a fault rupturing in the near future. The report identifies that most faults in the Taupō District are expected to have recurrence intervals in the order of 500 to 2000 years. The risk associated with individual properties or individual mapped fault lines is generally unknown.

GNS Science advises that potential damage for buildings and infrastructure built across a fault line can be considerable. However, the GNS Science report notes that from about two dozen buildings, typically single-story timber-framed houses, barns and woolsheds that have been directly impacted by surface fault rupture in recent New Zealand earthquakes, none of these buildings collapsed, and from a life-safety perspective all of these buildings performed well [page 108 refers].

For more information, read the full GNS Science report.

GNS report: active faults in the Taupō District (PDF, 18MB)

This information will eventually be included in the District Plan, including rules for future building and development in these hazard areas. Additional building consent requirements will apply to new buildings in Fault Avoidance Zones. Any existing buildings and development will be allowed to remain.

We will be considering and developing rules, including public consultation as part of our District Plan review. The review will consider the recommendations from GNS Science and the national guidance from the Ministry for the Environment.

The Fault Avoidance Zones have been identified and mapped using Light Detection and Ranging (LIDAR) ground maps. This is the most accurate way to identify faults for a large area. Better information can only be gained through excavation and trenching, which is costly. We have no plans in place to amend or update these maps in the foreseeable future.

The Fault Awareness Areas have been identified using faults previously identified in GNS Science’s active fault data base, and applying a buffer to recognize the uncertainty surrounding the mapped location of these fault lines. This method has been undertaken because Light Detection and Ranging (LIDAR) ground maps are not currently available in these areas to more accurate identify and map fault lines. However, Waikato Regional Council is planning to get LIDAR ground maps for the whole of Taupo District in 2021. When these new maps are available it will be possible to reduce the wider Fault Awareness Areas to the narrower and more accurate Fault Avoidance Zones. This may give property owners an opportunity to narrow the affected area on their properties, or if there are problem areas that affect many properties or potential development areas, Council may consider refining the fault line mapping in these areas.

If you apply for a building consent, you will be required to get geotechnical advice for the site you wish to build on. This is a standard process for most building work in our rural areas.

Expert advice is that building in these areas should be avoided where possible. If you apply for a building consent, you will be required to get geotechnical and engineering advice to assure Council that new building work can be done and engineered in a way that mitigates the risks associated with any faults.

We recommend you consult your insurance policy and/or contact your insurance provider to see if there are any implications as we cannot provide advice in this area.

There are many factors which affect property values. The risks posed by natural hazards may be one of them, and a registered property valuer may be able to advise on any enquiries regarding property value.

The fault line maps will be publicly available information. Where fault lines impact on a property, this will be identified on future LIMs (Land Information Memoranda), until such time as new District plan maps and rules are adopted. Council is required to put this information on property LIMs.

Previously the district had around 380 properties and around 50 houses or buildings on or within 20 metres of mapped fault lines. More accurate mapping of existing fault lines and the detection of new fault lines means the district now has around 820 properties containing Fault Avoidance Zones or Fault Awareness Areas. There are around 110 buildings that are now considered to be in Fault Awareness Areas and around 200 buildings now in what are considered Fault Avoidance Zones.

Anywhere could be impacted by a significant earthquake which could affect many buildings and houses as well as major infrastructure like water, roads, bridges, electricity, internet and cell phones. You should be prepared with an emergency plan, get away kit, and emergency survival items. For more information on what you should do, head to www.getready.govt.nz/emergency/earthquakes/