New research has revealed that a fault line south of Auckland, New Zealand's largest city, is active and could produce a 6.8 magnitude earthquake. This contradicts the long-held local belief that the region was largely immune to intense seismic activity. The Mangatangi Fault, located roughly 50km southeast of central Auckland along the Hunua ranges, has ruptured in the past 10,000 years, according to a study published in the New Zealand Journal of Geology and Geophysics.
Geologist Dr James Muirhead, co-author of the study, warned that if the entire fault ruptured, it would likely cause serious consequences for South Auckland and possibly central areas. The research is the first to radiocarbon date a fault line in Auckland or the Hunua Ranges, revealing how little is known about the region's seismic history. Anna Kaiser, chief scientist for earthquake hazards at Earth Sciences NZ, noted that while the study alone may not alter the national seismic hazard model, it is crucial for local preparedness.
This discovery comes after Auckland's mayor, Wayne Brown, successfully lobbied the government in 2023 to exempt the city from earthquake-prone building regulations, arguing no significant earthquakes had occurred in 100,000 years. The government granted the exemption in 2025, meaning no strengthening work is required. Mayor Brown dismissed the new research as "nonsense," claiming Auckland's geology is different. However, Muirhead suggests the city's hazard risk may be "significantly higher" than believed, and further research is needed to determine if current building regulations are adequate. The minister for building and construction, Chris Penk, stated that a single study does not warrant an immediate regulatory change.