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Seismic Wairarapa: Four new faults found in the region

One of the four newly discovered faults runs under Papawai Marae. PHOTO/GRACE PRIOR

Grace Prior

Four new potentially active faults have been discovered in Wairarapa this year after ongoing scientific research in the region.

The discovery was discussed at Greater Wellington Regional Council’s Civil Defence Emergency Management meeting on Tuesday.

The meeting agenda said active fault mapping had detected the new faults.

Two of the four new faults were found in Greytown. The faults included the Woodside fault, located in the outskirts of Greytown and trending towards the town, and the Papawai fault, which extended southeast of Greytown and beneath the Papawai Marae.

A fault was also found to the southeast of Carterton, named the Carters Line Fault.

The final fault, the Ruamahanga fault, was situated northeast of Masterton.

The meeting agenda said the faults were identified from their expression in the landscape using light detecting and ranging data.

The finding was included in the “It’s Our Fault” research programme statement for 2022 and 2023.

Some of the faults had broad, gentle scarps and extended through areas that were altered by humans or alluvial processes.

“Little is known about these faults because of this and their proximity through or near urban areas.”

The faults needed further study to confirm whether they were active, the time between earthquakes, and how fast the land was slipping.

The next steps to address the lack of information about the activity of faults included a non-invasive ground penetrating radar [GPR] study.

“Multiple transects will be run across each fault, utilising GNS Science’s newly acquired GPR, and the resulting profiles will be analysed to determine whether evidence of faulting is present.”

Further research would explore the ages of terraces cut by faults and any effects this may have on fault activity.

Scientists would also find sites for future investigation and speak with iwi and landowners to “develop relationships and obtain permissions for future trenching”.

The newly found faults added to the Wairarapa Fault and the Hikurangi Subduction Zone found within and on the coast of Wairarapa.

Te Ara said New Zealand’s largest recorded earthquake happened on the Wairarapa Fault in 1855.

The quake reached magnitude 8.2, uplifting the land by up to 6.4 metres and moving it horizontally by 18m.

All Civil Defence Emergency Management Group members moved to approve the proposed milestones included in the statement of work, including further research into the faults.

Masterton District Council chief executive David Hopman and Carterton District Council chief executive Geoff Hamilton agreed that further research would help future planning for councils.

They said the research would be included in the Wairarapa Combined District Plan, which was under review.

South Wairarapa Mayor Alex Beijen said the effect the faults could have on earthquake strengthening could not be gauged until “definitive information” was received.

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