Seismic Risk Zones in New Zealand — What They Mean for Your Building
New Zealand sits on the boundary of the Australian and Pacific tectonic plates, making it one of the most seismically active countries in the world. But seismic hazard is not uniform across the country. Understanding where your building sits in the national hazard picture is useful context — though as this article explains, hazard zone alone doesn't determine what's required for your building.
How seismic hazard is measured in New Zealand
New Zealand's seismic hazard is quantified using peak ground acceleration (PGA) — the maximum ground acceleration expected at a site over a given return period. The relevant standard for building design is NZS 1170.5 (Structural Design Actions — Earthquake Actions), which maps hazard zones based on PGA values.
The highest mapped hazard regions include Wellington, Marlborough, Hawke's Bay, and the central South Island — areas close to major fault systems including the Wellington Fault, the Alpine Fault, and the Hikurangi subduction zone.
Canterbury is worth noting separately. The Canterbury Plains have lower mapped PGA than Wellington — but the 2010–11 earthquake sequence demonstrated that mapped hazard can significantly underestimate local ground motion due to soil amplification and previously unknown fault sources. The pre-2010 assumption that Christchurch was a moderate-risk city proved incorrect in practice. This is relevant to any building owner who treats mapped hazard as a ceiling rather than a floor.
Hazard zone versus Importance Level — what actually drives requirements
A common misconception is that being in a high-hazard zone automatically determines what's required for your building's gas systems. In practice, the primary driver is not the hazard zone but the building's Importance Level (IL) under NZS 4219 (Seismic Performance of Engineering Systems in Buildings).
NZS 4219 classifies buildings by IL based on occupancy and post-disaster function:
- IL 1 — minor structures with low occupancy
- IL 2 — standard commercial and residential buildings
- IL 3 — buildings that must remain operational after an earthquake — schools, large assembly buildings, high-occupancy facilities
- IL 4 — buildings essential to post-disaster response — hospitals, emergency services, critical infrastructure
For IL 3 and IL 4 buildings, NZS 4219 sets more stringent requirements for the seismic performance of mechanical services, including gas systems. Whether automatic gas isolation is required for a specific building depends on the IL, the gas system configuration, and how the consent is structured — but seismic isolation of gas systems is part of the compliance framework for higher-importance buildings across all hazard zones. An IL 4 hospital in Auckland faces the same compliance framework as one in Wellington, even though the mapped hazard differs.
What this means for building owners
For IL 2 buildings — the majority of commercial stock — automatic gas isolation may not be a code requirement, but the risk calculation is straightforward. If a moderate earthquake damages gas pipework and supply isn't automatically isolated, gas continues to flow until someone manually shuts it off. In a building that has just been evacuated, that may take minutes. The consequence is the same regardless of whether the building is in Wellington or Auckland.
For IL 3 and IL 4 buildings, the compliance question should be resolved at consent stage, not after an event.
Matching sensitivity to location and application
The Solid State Seismic Shutoff — MK6 has five sensitivity settings, adjustable in the field via DIL switch: 0.012g, 0.025g, 0.050g, 0.100g, and 0.200g. These figures are specific to the MK6 — not a general industry range.
The right setting depends on the location, the consequence of a false trigger, and the application. A Wellington hospital installation on the most sensitive setting will trigger on any detectable seismic event. An industrial facility in a lower-hazard region where a false shutdown is operationally costly may be set to a higher threshold. The field-adjustable design means the threshold can be reviewed and updated as the building use changes.
Finding out what applies to your building
Your building's Importance Level and mapped seismic zone should be documented in the building consent. For older buildings where consent documentation is incomplete or inaccessible, a structural or building services engineer can confirm the IL — or you can contact your territorial authority or refer to MBIE guidance on building classifications. If seismic gas isolation is required, or if you want to add it as a precautionary measure, we can advise on the right specification for your location and application.
Solid State Seismic Shutoff — MK6 — full product details →