3D scanning reveals new active faults in Wairarapa

Scientists have revealed several new active faults in Wairarapa – the latest in a series of new discoveries using 3D laser scanning technology. Photo / File

Scientists have revealed several new active faults in Wairarapa – the latest in a series of new discoveries using 3D laser-scanning technology.

The faults were uncovered by a GNS Science team as part of a revision of Wairarapa’s Combined District Plan, which required up-to-date information on local natural hazards.

Some were found southeast of Carterton crossing Carters Line, and west and southeast of Greytown near Woodside and Pāpāwai, while another series of northeast-orientated faults were identified to the north of Masterton, between the township and Mokonui faults.

The team, which had prioritised mapping the most important faults and those near Wairarapa’s towns, have developed new “fault avoidance zones”, where they recommended that any structures or activity should be set back.

“Knowing where active faults lie in our regions is important, particularly for town planning purposes,” GNS earthquake geologist Dr Nicola Litchfield said.

“Having the best information about local earth structures and being able to forecast where movement is likely to occur in a significant earthquake means regions have the ability to plan better for hazard resilience.”

Wairarapa – lying near the Hikurangi Subduction Zone, where the Pacific and Australian Plates collide – was already known to be home to a multitude of local faults.

Its best-known, the Wairarapa Fault, extended from near the coast, just southwest of Lake Wairarapa, and ruptured in 1855 to create the magnitude 8.2 Wairarapa Earthquake.

Scientists were gradually gaining a clearer picture of the Greater Wellington region’s earthquake hazard with the “It’s Our Fault” programme.

What’s called LiDAR, or light detection and ranging tech, enabled scientists to map landscapes in high resolution, and peer through forests and buildings to reveal the earth structures - and sometimes undetected faults - lying beneath.

“We tend to call them ‘new’ faults, but of course they have been around for tens of thousands of years, they are just new to us,” Litchfield said.

GNS scientists recently used the same tech to uncover hundreds of ancient landslides around Pukekohe, along with a new multi-dimensional view of the region’s active faults and volcanic features.

Scientists considered a fault to be active if it’d been known to move within the past 125,000 years. Recently released sophisticated seismic hazard models have changed our understanding of the country’s earthquake risk.

The updated National Seismic Hazard Model found New Zealand’s “shaking hazard” had grown, on average, by 50 per cent or more in most locations.

But that didn’t mean the risk of earthquakes themselves had risen, with experts putting the increased calculations down to what they’ve learned from a decade of quakes and new science.

Meanwhile, the New Zealand Community Fault Model - described in a recently published study - mapped 900 faults capable of generating moderate to large quakes.

This week, Litchfield and GNS paleoseismologist Genevieve Coffey were back in Wairarapa collecting soil samples that’d help date landforms offset by faults up to tens of thousands of years ago.

“All of the information we can glean from the earth beneath our feet provides a snapshot of fault history, and helps us forecast what might happen in future,” Coffey said.

“New Zealand is very familiar with natural hazards and their risks and impacts. We experience a lot of earthquakes, with some significant ones in our recent history.”