New research has identified an active fault south of Auckland capable of generating a significant earthquake, prompting renewed scrutiny of the seismic risks facing New Zealand’s largest city and raising questions about recent decisions to exempt the region from certain earthquake-strengthening requirements.

The study, published in the New Zealand Journal of Geology and Geophysics, found that the Mangatangi Fault, located in the Hunua Ranges about 50 kilometers southeast of central Auckland, has ruptured within the past 10,000 years. Researchers estimate the fault could generate an earthquake of up to magnitude 6.8 if it were to rupture along its full length.

The findings challenge a long-standing perception that Auckland faces relatively low earthquake risk compared with other parts of New Zealand. While the city remains less exposed to major seismic hazards than many regions further south, scientists say the research highlights significant gaps in understanding Auckland’s geological history.

Dr. James Muirhead, a senior lecturer in geology at the University of Auckland and a co-author of the study, said the consequences of a major rupture could be severe for communities in southern parts of the city and potentially beyond.“If the whole fault ruptured, there would likely be serious consequences for people living in South Auckland, and possibly further into central Auckland as well,” Muirhead said.

The research marks the first time a fault in the Auckland region or the Hunua Ranges has been dated using radiocarbon techniques to determine when it last moved. Scientists classify a fault as active if it has ruptured within the past 125,000 years.According to Muirhead, the study demonstrates how little is currently known about the seismic history of the Auckland region and underscores the need for further investigation into local fault systems.

New Zealand lies along the boundary between the Pacific and Australian tectonic plates, making it one of the world’s most seismically active countries. The country records approximately 20,000 earthquakes annually, although only around 250 are generally strong enough to be felt by residents.Some earthquakes have had devastating consequences.

The 2011 Christchurch earthquake, which measured magnitude 6.3, killed 185 people and caused widespread destruction across the city’s central business district.Historically, most significant earthquakes in New Zealand have occurred in the South Island and the lower North Island. Auckland experiences occasional minor tremors but has generally been regarded as having a lower probability of damaging earthquakes.

That assessment played a role in policy discussions over earthquake-prone buildings. In 2023, Auckland Mayor Wayne Brown argued that the city’s low seismic risk justified changes to national building regulations. He cited the absence of evidence for major earthquakes affecting Auckland over a period of approximately 100,000 years.

The government subsequently announced in 2025 that Auckland would be exempt from earthquake-prone building rules, meaning many structures in the city would not be required to undergo costly seismic strengthening.The new findings have prompted some researchers to question whether the current regulatory framework fully reflects the region’s geological realities.

Muirhead said additional research is needed before drawing firm conclusions about whether existing legislation should be revised. While future investigations could ultimately show the risk is lower than currently estimated, they could also reveal that Auckland faces a greater hazard than previously believed.“We could see that the risk is actually lower than what we think right now, but we could also collect data and find actually it’s a little bit higher, and at that stage we should really think about whether we have the right legislation for buildings in the city,” he said.

Scientists caution that a single study is unlikely to dramatically alter Auckland’s position within New Zealand’s national seismic hazard assessments. The country’s seismic hazard model, updated by GNS Science in 2022, continues to show that Auckland faces lower levels of earthquake shaking risk than many other regions.

Anna Kaiser, chief scientist for earthquake hazards at Earth Sciences New Zealand, said the study is nevertheless valuable because it contributes important local data that can be incorporated into future hazard assessments.According to Kaiser, the findings improve understanding of Auckland’s geological environment and help refine long-term risk models. She emphasized the importance of preparedness and evidence-based planning rather than alarm.

The government has indicated that it will review emerging scientific findings as more information becomes available. Building and Construction Minister Chris Penk said the new research would be considered as part of ongoing assessments, but stressed that one study alone does not justify an immediate change in regulatory settings.

Mayor Brown rejected suggestions that the findings significantly alter Auckland’s risk profile. In comments responding to the study, he argued that the geological conditions beneath much of Auckland differ from those surrounding the fault zone identified by researchers.Scientists involved in the study say further investigations are now needed to determine whether other faults in and around Auckland may also be active.

They argue that building a more complete picture of the region’s seismic history is essential for informed urban planning and risk management in a metropolitan area that is home to more than one-third of New Zealand’s population.

For researchers, the objective is not only to better understand Auckland’s geological past but also to ensure that future planning decisions are guided by the most comprehensive evidence available, helping reduce the potential impact of any major earthquake that could occur in the region.