National Seismic Hazard Model

Overview of the National Seismic Hazard Model

The National Seismic Hazard Model (NHSM) provides an estimate of the likelihood and strength of earthquake shaking that might occur at any given site in New Zealand. The model helps deliver science-based estimates that are essential for New Zealand to build risk assessments and manage risks to safety, security and the economy from seismic events.

The NSHM is a part of New Zealand’s science ‘infrastructure’, helping to inform technical standards for earthquake engineering design as well as providing critical information for earthquake risk management relevant to insurance, infrastructure management and emergency planning and response.

The model is used broadly by organisations and decision makers that need to estimate the likely impact of earthquakes on our land, buildings, and infrastructure.

The model is used to guide seismic risk communication for civil defence planning and community resilience, for road and rail infrastructure planning, and to help insurance companies assess risk. It helps in the management of government owned assets and in determining how buildings and structures need to be designed and built so they inform the risk settings of our building regulations requirements in relation to earthquake loadings.

GNS Science (GNS) is the custodian of the model. The model was originally created in the 1980s, with the most widely used version of the model developed in 2002. The 2002 NSHM informed the development of the seismic loading requirements in NZS1170.5:2004, which is referenced in the Building Code. The NSHM was updated with new data in 2010, but with minimal science revision. The 2010 update is used by insurers and in the design of special buildings but was not adopted into the Building Code or Bridge Manual.

The NSHM is essential for:

• identifying the loads used to design buildings to ensure they withstand future earthquakes and minimise risk to life.
• providing a picture of New Zealand’s seismic hazards.

Revision of the National Seismic Hazard Model

In 2020, MBIE and Toka Tū Ake EQC commissioned GNS to review the NSHM and provide an updated version of the model. Since the last update of the NSHM in 2010, there have been significant advances in science modelling capability and data collection. This, in addition to learnings from the Canterbury earthquake sequence and Kaikōura earthquake and input from scientific and academic experts, means that we can deliver more robust and up-to-date science-based estimates that are essential for New Zealand.

In 2022, this revision of the NSHM was released. The model and results are freely available from the GNS website.

National Seismic Hazard Model — GNS Science

Using the updated National Seismic Hazard Model

MBIE uses the NSHM to help inform the risk settings in our building regulations and to improve the safety of buildings across New Zealand.

The 2022 NSHM results do not automatically change how we design buildings. Building professionals and practitioners should continue to use existing law, technical standards and guidance to demonstrate that their work complies with the Building Code.

New buildings

We will carefully consider what the updated NSHM means for new building design standards. We are currently working with Engineering New Zealand to assess what changes to building design standards are required, and how to include the NSHM results in regulatory settings for new buildings. We will consult on any changes to building design standards as part of future Building Code updates.

We encourage engineers to use new information released by the engineering technical societies NZSEE, SESOC and NZGS. This information recommends the approaches an engineer can take to help ensure reliable seismic performance from a building, regardless of uncertainty in the seismic hazard.

Earthquake Design for Uncertainty Guidance — NZSEE

Until any changes are made to the Building Code documents, engineers should continue to use the existing version of B1/VM1 to demonstrate that the design of structures complies with the minimum performance requirements in the Building Code. We encourage the sector to keep designing to the highest possible safety standards where practical.

B1 Structure | Building Performance

Existing buildings

The updated NSHM results do not change the way seismic assessments are done. In collaboration with the engineering technical societies NZSEE, SESOC and NZGS, we are currently considering if any changes to the hazard used in seismic assessments will be needed once updates to new building design standards is complete. Until then, engineers can continue to use the seismic hazard specified in B1/VM1 for voluntary assessments.

Earthquake-prone buildings

The updated NSHM results do not change the requirements of the earthquake-prone building system. The earthquake-prone building system uses the seismic hazard specified in B1/VM1 on the date the legislation came into effect which was July 2017. Owners who have assessed and remediated their buildings cannot be asked to do so again.