Researchers are exploring the possibility of a future earthquake along the Nevis-Cardrona Fault in West Otago

Researchers have dug a trench near the Nevis-Cardrona Fault in West Otago to determine when prehistoric earthquakes occurred. Credit: University of Otago

A new study has revealed that the likelihood of a future earthquake along the Nevis-Cardrona Fault in West Otago is lower than previously thought.

The study, published in the journal Seismica, also provides new constraints for estimating earthquake risk around the fast-growing Queenstown-Wanaka region.

Led by the University of Otago-Otaku Wakaihu Waka, researchers drilled the southern part of the fault to determine when the prehistoric earthquakes occurred.

While doing so, they discover new information that updates research from the 1980s.

Lead author Dr Jack Williams, from the Department of Geology, says previous studies recognized the possibility of future earthquakes, but their rate and magnitude were unclear.

“Our new data suggest that the rate of the prehistoric Neves-Cardrona earthquake is lower than these previous studies estimated,” he says.

“Although it does serve as a reminder that earthquakes can happen anywhere across Aotearoa, and we all need to prepare and plan accordingly.”

This work is also part of a broader effort by the group to characterize more than a dozen major active faults in the Otago region, says Professor Mark Stirling, head of the Department of Earthquake Sciences.

Knowing when past earthquakes occurred creates insight into future earthquakes, he says.

Publishing in the journal Seismica, the researchers analyzed different geological layers in trenches across the fault and used dating methods to obtain the timing of prehistoric earthquakes.

When they see evidence in the topography of previous surface rupture, they can dig trenches perpendicular to the fault, which are typically 30 meters to 40 meters long, 6 meters deep and 7 meters wide, Dr. Williams says.

“On the walls of the trench, we then analyze how different sediments have been displaced and moved by previous earthquakes that tore up the ground along this fault,” he says.

“Most importantly, we want to know how many earthquakes must have occurred to explain the pattern of sediments in the trench wall, and then collect samples of these sediments that we can date.”

To date the sediment, researchers use a technique called optically stimulated Luminesce dating, which measures the last time the sediment was exposed to sunlight.

“From these results, we can then determine the timing of the earthquakes that deformed the sediments.”

Researchers believe that sediments from the Neves-Cardrona fault were exposed by two earthquakes, about 12,800 years ago and sometime between 20,000 and 40,000 years ago. By comparison, previous research has concluded that four earthquakes have occurred in the past 20,000 years.

Dr. Williams says the study results differ from research conducted 40 years ago because seismology has advanced since then.

Previous fault investigations have been carried out to assess seismic hazards during hydropower development in the Clutha River catchment.

“It was one of the first detailed studies of ancient fossils in New Zealand, and this work was, at the time, very forward-thinking,” he says.

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“In the 1980s, the only way to derive the age of sediments, and thus determine the timing of past earthquakes, was through radiocarbon dating. However, carbon is very scarce in the near-surface soils of Central Otago so they were only able to find carbon and extract the timing of the earthquakes.” From one trench.

“In other places, the timings of past earthquakes were just an educated guess.”

“With the subsequent development of dating techniques, the lack of carbon was no longer an obstacle to obtaining the timing of earthquakes, and the cumulative dates we obtained from trenches in the upper Nevis Valley indicate lower seismic rates than previously estimated.”

NHC head of research, Dr Natalie Balfour, says research into understanding earthquake risk feeds into community education and risk modeling programmes, helping communities better prepare for future events.

“While the data in this case shows that earthquakes in this part of Otago have occurred less frequently than previously thought, any part of the country could experience a devastating earthquake or damage from a large tremor further away. Wherever you live, it's a good idea To secure your home from earthquakes, know your insurance cover and prepare emergency supplies.”

More information: Jack Williams et al., The extent of extensional earthquakes on multisegment reverse faults; Insights from the Nevis-Cardrona Fault, Aotearoa New Zealand, Earthquake (2024). doi: 10.26443/seismica.v3i2.1310

Provided by the University of Otago

Citation: Researchers explore potential for future earthquake along the Nevis-Cardrona Fault in West Otago (2024, December 12) Retrieved December 13, 2024 from https://phys.org/news/2024-12-explore-likelihood-future- quake-nevis.html

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