Past could be key to forecasting future quakes

New Zealand's caves could yield our ancient quake history - and help us better forecast big events in the future. Photo / File

When it comes to forecasting major quakes in New Zealand's future, the answers might lie hidden in our past.

Or more precisely, in our caves.

A team of scientists will search for clues in cave systems across the country to reveal ancient earthquakes - something that could help better prepare us for big events to come.

While decades of research have given us a world-class database of active faults, along with a good understanding of major pre-history quakes along well-known faults, the recent shakes that have hit the country have shown us how much we don't know.

The 7.1 quake that struck near Darfield in 2010, setting off the Canterbury earthquake sequence, occurred on a previously unrecognised fault, while the incredible complexity of November's 7.8 Kaikoura Earthquake surprised scientists, rupturing more than a dozen faults.

A record of previous large quakes is essential for trying to work out the future risks we face, but scientists have long been hampered by a lack of such evidence.

That's partly due to the relatively short time people have lived in New Zealand and the ancient geological record having not been preserved well enough in our ever-changing landscape.

This has made it difficult to accurately draw out the long-term intervals between past quakes have happened, as well as recording quake clusters that have struck within a century.

Now, a new study, awarded a million-dollar grant by the Government's Endeavour Fund, aims to overcome these challenges with a new tool for detecting and dating earthquakes - and potentially uncovering old quakes in parts of the country where there's little activity today.

Much of it will be informed by geochemical investigations of cave deposits - namely speleothems, or natural formations like stalactites and stalagmites - found throughout New Zealand.

The University of Auckland-led research team believe these deposits would bear marks of old quakes, which would have caused some formations to break and fall to the floor, or tell-tale changes in water flow through the caves.

By dating the tips of broken or oddly-grown chunks of these formations, and pin-pointing geochemical signs, they expect to push our earthquake record back hundreds of thousands of years, while also adding much new detail.

Interestingly, the Kaikoura Earthquake offers them a unique opportunity to ground-truth their methodology.

The team will investigate that quake's impact on nearby caves, and search for damage and effects in other cave sites around the country that can be compared with similar signs of ancient quakes at the same sites.

The approach could even allow scientists to assess whether big quakes have struck in the upper North Island and, if so, how often.

With recent loss estimates for a 9.0 quake and tsunami generated from the Hikurangi Margin subduction zone killing more than 12,500 people and costing more than $20 billion, the researchers argued there was an "ever-pressing need" to better understand quake risk.

The researchers are about to begin another Marsden Fund-supported study, using the same method, to better define the timing and environmental effects of past volcanic eruptions.