Professor David Lowe, Dr Jordanka Chaneva and Dr Max Kluger. Photo/ Supplied
Researchers at the University of Waikato have found hidden fault lines beneath Hamilton and the Hauraki Plains which have caused several magnitude 7 earthquakes over the past 15,000 years.
Emeritus Professor David Lowe said while Hamilton’s earthquake risk remained low to moderate, the research allowed communities to plan better and to better understand the long-term hazards posed by earthquakes.
In a multidisciplinary effort, scientists turned to technology more commonly associated with hospitals than geology labs.
Using 3D CT scanning, the team analysed sediment samples drawn from ancient lakes across the Hamilton Basin – some dating back 20,000 years.
The samples, narrow tubes of organic-rich mud extracted with their delicate layering intact, revealed distinctive deformation features known as tephra seismites – layers of volcanic ash that liquefied during strong ground shaking.
CT imaging allowed researchers to view these features in unprecedented detail, measure their size and structure, and enable a new method for reconstructing the region’s earthquake history.
With the new approach, the team could detect and date large prehistoric earthquakes even when the faults themselves were completely buried, Lowe said.
Faults are cracks or fractures in the Earth’s crust. A fault line is an area of related cracks.
“The known ages of ash layers allowed us to determine when the earthquakes occurred.
“Our analysis showed where the strongest ground shaking occurred and helped identify which fault ruptured and when,” Lowe said.
The research is the first detailed reconstruction of prehistoric earthquake activity in the Hamilton Basin, which stretches about 80km from Ngāruawāhia to Te Awamutu and roughly 50km west to east.
The research identified structures that include the hidden Kūkūtāruhe and Te Tātua ō Wairere faults beneath the Hamilton lowlands, as well as the Te Puninga and Kerepehi faults in the Hauraki Plains.
Data from the study also points to a previously unrecognised fault near Te Awamutu.
Lowe said the lake-preserved seismites functioned like natural seismographs, preserving evidence of past quakes and unseen hazards.
Radiographer Nic Ross from I-MED Hamilton Radiology helped the team scan 161 lake mud samples from 18 lakes, placing them on a CT scanner to create clear digital images.
Three of the four mapped faults are believed to have ruptured at least once.
Despite the findings, researchers emphasised that Waikato remained a low-to-moderate seismic risk region.
“This doesn’t mean the short-term earthquake risk has increased,” Lowe said.
“What it means is that we now understand the long-term hazard much better, and that knowledge helps communities plan, particularly for critical infrastructure such as hospitals, power facilities and transport networks.”
On average, strong shaking appears to have affected the wider Hamilton–Hauraki region roughly every 3000 years.
“That doesn’t mean one is about to happen tomorrow,” Lowe said.
“But it does show the area has a genuine earthquake history.”
The new findings will be incorporated into the New Zealand Community Fault Model, which informs long-term seismic hazard planning for essential services.
Earth Sciences New Zealand earthquake geologist Dr Pilar Villamor, also part of the research team, said lessons from the 2010–11 Canterbury earthquakes underscored the risks posed by hidden faults.
“Even though a large earthquake is very unlikely within most people’s lifetimes, Hamiltonians should still be prepared for strong shaking,” she said.
“Having an emergency plan and kit is essential.”
The four-year research project was led by Professor Lowe with Dr Max Kluger, Dr Vicki Moon, and Dr Tehnuka Ilanko.
It involved graduate students and collaborators from Earth Sciences New Zealand, University of Auckland, I-MED Hamilton Radiology, and Swansea University in the UK.
The research was supported by iwi, including Ngāti Wairere and Ngā Iwi Tōpū o Waipā, as well as local and regional councils and the Department of Conservation.
Tom Eley is a multimedia journalist at the Waikato Herald. Before he joined the Hamilton-based team, he worked for the Weekend Sun and Sunlive. He previously worked as a journalist in Canada for Black Press Media and won a fellowship with the Vancouver Sun.