18 months ago by Helen Shea
A team of scientists will be learning more about the Hikurangi plate boundary over the next two weeks aboard NIWA’s research vessel, Tangaroa.
The scientists will be collecting data to better understand how the plate boundary is moving and evidence of past earthquakes off the east coast of the North Island. A key question of their research is whether the Hikurangi boundary is capable to producing devastating great (>M 8) or giant earthquakes (>M 9).
The Tangaroa departed Wellington on Saturday with a large team of New Zealand and international scientists who are studying the Hikurangi plate boundary. Kate Boersen from East Coast LAB (Life at the Boundary) will be on board to share the work being done with the public (via www.eastcoastlab.org.nz).
“I’m looking forward to be able to share this research with everyone along the East Coast and Hawke’s Bay so we can all benefit from the knowledge gained,” says Kate.
“This information can add to our knowledge of earthquakes and tsunami risks along this coast, something we all need to understand better so we can be prepared.”
Dr Laura Wallace, GNS Science geodetic scientist, is leading the voyage which includes 19 scientists from GNS and NIWA, and international scientists from Japan and the USA, plus crew.
During the first part of the voyage, scientists will be retrieving five seafloor pressure instruments and redeploying nine more off the Mahia and Gisborne coasts. They will record information continuously on the seafloor and will be collected next year and further instruments deployed to replace them.
Seafloor pressure instruments are capable of sensing vertical movements of the seafloor as small as one centimetre, and also track the passage of tsunami waves. The sensors measure the pressure exerted on the seafloor by the overlying water, so if the seafloor moves up or down this is recorded as a pressure increase or decrease. Seafloor movement is most obvious during earthquakes, such as the recent Kaikoura earthquake, or periods of small tremor know as slow-slip events. Sensors deployed previously offshore Gisborne have recorded 1-7cm of seafloor movement as a result of slow slip events.
Dr Wallace is keen to see what the instruments have recorded from the Te Araroa earthquake and tsunami in September 2016, and from a slow-slip tremors triggered offshore Gisborne by the Kaikoura earthquake in November 2016.
“This should help us to better understand the behaviour of the Hikurangi plate boundary, which is New Zealand’s largest and most active plate boundary fault,” says Dr Wallace.
A port stop in Gisborne will enable more scientists from NIWA and Victoria University to join the voyage to take sediment cores from the seafloor.
The scientists will be looking for geological evidence in the cores of landslides caused by strong ground shaking to try to reconstruct where and when earthquakes have occurred along the Hikurangi plate boundary.
“We are looking for specific sediment layers that are triggered by ground shaking (earthquakes), transported down-slope and eventually settle on the seafloor. These dense clouds of mud and sand are know as marine ‘turbidites’” says NIWA marine geologist Dr Alan Orpin.
The Hikurangi plate boundary research is part of a five-year Ministry of Business, Innovation and Employment (MBIE) research programme called ‘Diagnosing peril posed by the Hikurangi subduction zone: New Zealand’s largest plate boundary fault’.