Previously Unknown Faultlines Discovered Under Auckland

Auckland, New Zealand – Dozens of previously unknown faultlines have been discovered beneath Auckland, prompting further investigation into their potential seismic activity. While the discovery hasn’t immediately increased the perceived risk to the city, scientists are undertaking detailed analysis to determine if these faultlines are active and pose a significant hazard.

New Research and Active Faults

Researchers, including Auckland University senior lecturer James Muirhead, are defining active faults as those that have moved within the last 125,000 years . Some of the newly discovered faultlines may have remained dormant for up to six million years, classifying them as technically inactive. Others are considered suspected faults requiring further scrutiny.

Investigation Focus: Pukekohe and Drury

The initial phase of investigation will concentrate on areas near Pukekohe and Drury, located in Auckland’s rural south. Teams will excavate four-meter deep trenches across the faultlines to analyze how recently they have moved . Dr. Muirhead anticipates having a clearer understanding of the faultlines’ activity within approximately two years.

Auckland’s Seismic History

Despite a common perception of low seismic activity, Auckland has experienced significant earthquakes in the past, such as the 1891 Port Waikato quake, which caused damage including shattered windows within the city . The discovery of these new potential faults stems from analysis of borehole samples, examining subsurface movements over time .

Faultline Distribution

The research identifies three categories of faultlines: likely faults, possible faults, and possible structures. Two prominent probable faults run from the Waitematā to the Manukau harbours, passing through Avondale and from Glendowie to Blockhouse Bay. Possible faults are located around Northcote, Birkenhead, and Wiri, while numerous potential structures require further investigation in areas like Sandringham, Newmarket, and Ōtāhuhu .

Urbanization and Monitoring

The research suggests that intense urbanization may obscure the identification of faults. Improved monitoring has also revealed that Auckland experiences more small earthquakes than previously thought .

Funding and Land Use Implications

The work is partially funded by the Natural Hazards Commission (Toka Tu Ake), which highlights the findings in its latest Resilience Highlights Report. The commission notes that the research could influence land use decisions as the city continues to grow .

Related Research: Taupo Volcano

James Muirhead, from the University of Auckland, is also leading research into the seismic history of New Zealand’s Taupo volcano, using ground-penetrating radar to examine earthquake history over the past 25,500 years . This research aims to understand the relationship between volcanic and seismic activity in the region .