New research has cast doubt on Auckland's long-held perception of being largely immune to significant seismic activity, suggesting an active faultline could pose a serious threat to New Zealand's most populous city. The study, published in the New Zealand Journal of Geology and Geophysics, focuses on the Mangatangi Fault, situated about 50km south-east of Auckland’s city centre, near southern suburbs such as Pukekohe, Drury, and Takanini.
Led by Dr James Muirhead, a senior lecturer at the University of Auckland and co-author of the research, the findings indicate that the Mangatangi Fault has ruptured within the last 10,000 years. This places it firmly in the category of an 'active' fault, defined as one that has moved in the past 125,000 years. The research suggests a rupture could potentially trigger an earthquake of up to 6.8 magnitude, which could have serious consequences for residents in South Auckland and potentially central Auckland too.
This discovery directly challenges a recent decision to exempt Auckland from earthquake building regulations. In 2023, Auckland's mayor, Wayne Brown, successfully lobbied the government for this exemption, citing a perceived lack of significant seismic activity in the region over the past 100,000 years. The government subsequently announced in 2025 that the city would not be required to undertake strengthening work on earthquake-prone buildings. However, Dr Muirhead now warns that Auckland's hazard risk may be 'significantly higher' than currently understood by the public and policymakers, necessitating further investigation into the city's faultlines.
While New Zealand sits on the volatile boundary of the Australian and Pacific tectonic plates, experiencing approximately 20,000 earthquakes annually, Auckland has historically been considered at lower risk compared to the South Island and lower North Island. The national seismic hazard model, updated by GNS Science in 2022, still indicates a lower risk of shaking for Auckland. However, this new study marks the first time a faultline in the Auckland region or Hunua Ranges has been radiocarbon dated, providing precise information on its last rupture and highlighting gaps in understanding the region's seismic history.
Anna Kaiser, chief scientist for earthquake hazards at Earth Sciences NZ, acknowledged the study's importance in refining local knowledge and the national seismic hazard model, even if it doesn't immediately alter the broader picture of Auckland's relative seismic risk. In response, Chris Penk, the Minister for Building and Construction, stated that emerging research would be considered, but a single study does not warrant an immediate change to the proposed classification or regulatory approach. Meanwhile, Mayor Wayne Brown has dismissed the research as 'nonsense', citing different geological compositions beneath the city centre compared to the faultline's location.