Earthquake fault rupture hazards
In a major earthquake the ground may rupture, with ruptures typically occurring along existing fault traces. Therefore, any building built above a fault trace would be likely to be badly damaged.
The Council's District Plan includes provisions to try and avoid any new buildings being constructed above the fault trace. In most cases new buildings located above known fault traces will require resource consent.
What are the risks associated with Fault Rupture Hazards?
If a earthquake fault does rupture any building located over the fault is likely to suffer significant damage, creating a risk for occupants. For example, GNS has estimated that a rupture of the Ohariu Fault could result in between three and five metres of right-lateral displacement, with less and more varied vertical displacement.
The Council has adopted a risk-based approach to development and subdivision on or near earthquak fault traces. The District Plan seeks to avoid new buildings beign located on earthquake fault traces. In cases where this is not possible for building to avoid the mapped Fault Avoidance Zone, the council may require further geotechnical information from applicants to enable the Council to make an informed decision on whether to grant or refuse consent, or to impose conditions to minimise the risks of injury and damage to property.
Where are the faults within the District?
The Institute of Geological and Nuclear Sciences (GNS) has mapped all of the known active fault traces within the Kāpiti District. GNS identified Fault Avoidance Zones which are a buffer zone either side of the know active fault traces. The Fault Avoidance Zones are identified in the District Plan maps.
District Fault Zones Map (PDF, 1 page 1Mb)
It is possible that there are other active fault traces within the District that have not yet been discovered. It is also possible that the fault information will become more precise over time, in which case the size of the Fault Avoidance Zones shown on the map may be reduced.
What do we know about the earthquake faults in the Kāpiti Coast District?
GNS has provided information on the average recurrence interval, which is the estimated average interval between ruptures on an individual section or length of a fault. Also presented below are its estimates on when the District's fault last ruptured.
For example, the Ohariu Fault has an estimated recurrence interval of between 1,300 and 3,800 years and a last rupture of approximately 1,000 years ago. This does not mean that there is no risk from fault rupture at present but based on the best information available there is a low risk.
Ohariu Fault: Has an average recurrence interval of surface rupture of 1,300 to 3,800 years. The fault most recently ruptured approximately 1,000 years ago. It is expected that an individual surface rupture along the fault could generate three to five metres of right-lateral displacement at the ground surface, with a lesser and variable amount of vertical displacement.
Northern Ohariu Fault: Has an average recurrence interval of surface rupture of 1,000 to 3,000 years. The fault most recently ruptured approximately 300-1,000 years ago. It is expected that an individual surface rupture along the fault could generate three to four metres of right-lateral displacement at the ground surface, with a lesser and variable amount of vertical displacement.
Gibbs Fault: The activity and location of the Gibbs fault is less well constrained than both the Ohariu and Northern Ohariu faults. There is currently no information of the average recurrence interval or on when the fault last ruptured and it is anticipated that the Gibbs fault would have a longer recurrence interval than the Ohariu or Northern Ohariu faults. A 3,500–5,000 year recurrence interval has therefore been estimated.
Ōtaki Forks Fault: The average recurrence and timing of faults on the Ōtaki Forks fault is unknown. However, a 3,500–5,000 year recurrence interval has been estimated and the potential surface rupture has been estimated to be approximately one metre.
Southeast Reikorangi Fault: This is the fault about which the least is known. It is estimated that the recurrence interval of this fault is 5,000–10,000 years.
Source: Institute of Geological and Nuclear Sciences' report 'Earthquake Fault Trace Survey Kāpiti Coast District' (August 2003, updated August 2007).
The documents listed below are in PDF format and available for download or print.
- Planning for Development of Land on or Close to Active Faults: A guideline to assist resource management planners in New Zealand, GNS Science for the Ministry for the Environment (71 pages, 2Mb)
- Earthquake Fault Trace Survey, GNS Science (52 pages, 1Mb)
- Review of 2003 Earthquake Fault Trace Survey, GNS Science (4 pages, 508Kb)
- Northern Ohariu Fault: Review of geomorphologic evidence for an active trace (22 pages, 5Mb)
For additional information and reports on specific properties please contact one of our Policy Planners.