The study involved researchers excavating the southern part of the fault to determine when prehistoric earthquakes took place.
While doing so, they discovered new information which updated research from the 1980s.
Lead author and University of Otago geology researcher Dr Jack Williams said previous studies had recognised the possibility of future earthquakes, but their rate and size were unclear.
"Our new data suggests that the rate of prehistoric Nevis-Cardrona Fault earthquake is lower than estimated by these previous studies.
"Although, it does serve as a reminder that earthquakes can happen anywhere across Aotearoa, and we should all prepare and plan accordingly."
Researchers analysed the different geologic layers in trenches across the fault and used dating methods to obtain the timing of prehistoric earthquakes.
Dr Williams said where they saw evidence in the terrain of past surface-rupturing, they could excavate trenches perpendicular to the fault, typically 30m-40m long, 6m deep and 7m wide.
"On the trench walls, we then analyse how different sediments have been displaced and moved by the past ground-rupturing earthquakes along that fault.
"Most importantly, we want to know how many earthquakes must have occurred to explain the pattern of sediments in the trench wall, and then we collect samples of these sediments that we can date."
To date the sediments, researchers used a technique called optically stimulated luminesce dating, which measured the last time sediments were exposed to sunlight.
"From these results, we can then constrain the timings of earthquakes that deformed the sediments."
Researchers believed the sediments from the Nevis-Cardrona Fault experienced two earthquakes, about 12,800 years ago and sometime between 20,000-40,000 years ago.
Comparatively, previous work inferred there were four earthquakes in the past 20,000 years.
Dr Williams said the study’s findings differed from research done 40 years ago because earthquake science had progressed.
The previous investigations into the fault were conducted to assess earthquake hazards during the development of hydroelectricity in the Clutha River’s catchment.
"It was one of the first detailed paleoseismic studies in New Zealand and this work was, at that time, very forward-thinking.
"In the 1980s, the only way to derive the age of sediments, and hence constrain the timing of past earthquakes, was through radiocarbon dating.
"However, carbon is pretty rare in near-surface soils in Central Otago and so they were only able to find carbon and derive earthquake timings from one trench.
"Elsewhere, the timings of past earthquakes were an ‘educated guess’.
"With subsequent development of dating techniques, ... the dates we obtained from the trenches in the Upper Nevis Valley indicate lower earthquake rates than previous estimates."
The study was funded by a Natural Hazards Commission Toka Tū Ake University Research Programme grant. — APL
