Scientists deploy latest round of earthquake-monitoring equipment off NZ's east coast

Sunday, 14 October 2018

Scientists are placing more earthquake-monitoring instruments along New Zealand's largest fault, the Hikurangi subduction zone.

Scientists conducting research into our largest fault are installing the next round of earthquake-monitoring technology onto the seafloor to better understand the risks it poses.

The monitoring of the Hikurangi subduction zone is part of a larger, multi-year project which sees GNS Science leading research alongside other Crown agencies, councils and universities, into the zone - which runs along the east coast of the North Island.

In the current mission, the latest in a series of rolling deployments, about 30 instruments are being installed off the coast of Hawke's Bay, Gisborne and Wairarapa. On the same trip, scientists are recovering nine instruments deployed last year.

Once instruments have surfaced, scientists must look for red flags during the day, or bright flashing lights at night time, in order to recover the instrument.

Those nine instruments are seafloor pressure sensors, which record the upward and downward movements of the seabed at a centimetre-level, project leader from East Coast LAB, Kate Boersen said.

Scientists are deploying 30 instruments in this round; including seafloor pressure sensors, two arrays of precision seafloor transponders and several ocean bottom seismometers.

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The pressure sensors are able to monitor slow-slip earthquakes, which are earthquakes that occur from days to weeks to months, which aren't felt, Boersen said.

The team pictured with some of the instruments being deployed in the latest round off of New Zealand's east coast.

In addition to pressure sensors, there would also be ocean-bottom seismometers deployed, which record earthquakes.

'We often see seismic earthquakes during these slow-slip events, and so that will help us to better understand the relationship between these slow earthquakes, and the seismic, fast-moving earthquakes,' GNS Science's Dr Laura Wallace said.

Scientists are using the NIWA research vessel Tangaroa to deploy the instruments off the coast of Gisborne, Hawke's Bay and Wairarapa.

The final instruments being deployed are arrays of GPS acoustic transponders, which track the horizontal movement of the seafloor.

Wallace said this mission was more significant because scientists were putting a lot more instruments out than they had in previous years, and different kinds.

'We only have information about what's happened beneath the land, we actually need to know about this creeping-versus-stuck behaviour off-shore,' Dr Laura Wallace of GNS Science says.

Previously, scientists had focussed on the area off Gisborne, but this year instruments were also being put further south.

Initial data could 'hopefully' be extracted from the recovered instruments over the coming months, but for the 30 being currently deployed, they wouldn't be brought back up for another year, she said.

Current data showed the subduction plate boundary beneath the southern part of the North Island was 'stuck' and building up pressure, which 'probably will be relieved in a large earthquake one day'.

Whereas in the north, the boundary appeared to be 'creeping' without building up pressure.

'But we only have information about what's happened beneath the land, we actually need to know about this creeping-versus-stuck behaviour off-shore,' Wallace said.

Boersen agreed, saying scientists had identified places where slow-slip earthquakes were occurring, and where pressure may be building up, 'but what they don't know is the relationship between those two zones'.

Hawke's Bay Regional Council's environmental science manager Stephen Swabey said the research was exciting.

'The GNS Science work … demonstrates how effective collaboration can help us discover new things about the faults hidden underwater that might seriously affect Hawke's Bay in the future.'

Gisborne District Council chief executive Nedine Thatcher-Swann said it welcomed any research which helped the public understand the natural hazard risks the Tairāwhiti region faced.

The Earthquake Commission's research strategy manager Dr Richard Smith said the Hikurangi was a 'substantial hazard' for earthquakes and tsunami.