Earthquake studies converge on Gisborne 

FIELDWORK: Among the research team installing seismometers around the wider Gisborne area, in this case Waimata Valley, are Imperial College London PhD student Stephen Watkins, Victoria University summer scholarship student Laura Hughes, Cardiff University School of Earth and Ocean Sciences staff member Dr Ake Fagereng and Victoria University Masters student Danielle Lindsay. Picture by Liam Clayton

GISBORNE has been a hive of activity not only for revellers over the summer break. International seismologists are here studying the Hikurangi subduction zone.

Twenty scientists from New Zealand and the United Kingdom are investigating the zone for a research project called NZ3D FWI.

The team comprises researchers, technicians and students from international universities and organisations like GNS Science.

NZ3D FWI lead scientist and lecturer at Imperial College London, Dr Rebecca Bell, said the subduction zone is particularly shallow, which makes it more accessible and easier to study than others around the world.

It has attracted international interest and funding from scientists attempting to understand plate boundary tectonics and associated natural hazards, Dr Bell said.

“Gisborne is in a very special position because the subduction zone is really shallow beneath the surface.

“In places like Japan, the subduction zone is really deep at the coast.”

More than 200 seismometers have been installed in a grid around Gisborne and the East Coast.

“These instruments will record the ground shaking associated with earthquake activity and allow us to image the subsurface structure of the plate boundary lying off the east coast.

“We have what I am calling ‘a backbone grid’ of the bigger instruments every two kilometres over a 30 to 50km area.”

Many of the seismometers are spaced out around farm land in Waimata Valley.

Risks from farm animals

The only risk comes from farm animals, Dr Bell said.

“Most of the seismometers are in farmland so the hardest part is having to build fences to separate them from cattle so they don’t get trampled.

“Each seismometer involves digging an 80cm hole. They are powered by a solar panel and car battery.

“The instruments are very sensitive and pick up any movement, but it is clear to see what is cattle and what is earth movement when the data is collated.

“We are also putting 100 of them densely spaced every 500 metres in the Waimata Valley where there are mudpools and bubbling mud, to find out more about the mud-plumbing system.”

NZ3D FWI is part of a larger series of projects aimed at helping scientists understand the behaviour of the subduction zone to help minimise the risk posed to communities along the East Coast.

“All of the projects are focused on the geohazards and learning more about them,” Dr Bell said.

“What we learn here is important because we can compare with other data and figure out the true danger of the zone.”

Soundwaves and seismometers

Research vessel Marcus Langseth will be working off the Coast producing soundwaves and another ship will be installing underwater seismometers.

“We will collect seismic reflection data so the ship will produce soundwaves, which will travel through the subduction zone and reflect off boundaries between different types of rock and sediment,” Dr Bell said.

“These soundwaves will be detected by some of the seismometers on land and will show what the rock layers look like under water.”

The JOIDES Resolution, a drilling research vessel, is also offshore drilling more than 1.5km into the sea floor to find out more about underwater landslides and the Hikurangi subduction zone.

“In March next year I am coming back to New Zealand to go on board the JOIDES Resolution," Dr Bell said.

“We will install two earthquake observatories that will stay in place for up to a decade.”

The scientists are enjoying their stay in Gisborne.

GISBORNE has been a hive of activity not only for revellers over the summer break. International seismologists are here studying the Hikurangi subduction zone.

Twenty scientists from New Zealand and the United Kingdom are investigating the zone for a research project called NZ3D FWI.

The team comprises researchers, technicians and students from international universities and organisations like GNS Science.

NZ3D FWI lead scientist and lecturer at Imperial College London, Dr Rebecca Bell, said the subduction zone is particularly shallow, which makes it more accessible and easier to study than others around the world.

It has attracted international interest and funding from scientists attempting to understand plate boundary tectonics and associated natural hazards, Dr Bell said.

“Gisborne is in a very special position because the subduction zone is really shallow beneath the surface.

“In places like Japan, the subduction zone is really deep at the coast.”

More than 200 seismometers have been installed in a grid around Gisborne and the East Coast.

“These instruments will record the ground shaking associated with earthquake activity and allow us to image the subsurface structure of the plate boundary lying off the east coast.

“We have what I am calling ‘a backbone grid’ of the bigger instruments every two kilometres over a 30 to 50km area.”

Many of the seismometers are spaced out around farm land in Waimata Valley.

Risks from farm animals

The only risk comes from farm animals, Dr Bell said.

“Most of the seismometers are in farmland so the hardest part is having to build fences to separate them from cattle so they don’t get trampled.

“Each seismometer involves digging an 80cm hole. They are powered by a solar panel and car battery.

“The instruments are very sensitive and pick up any movement, but it is clear to see what is cattle and what is earth movement when the data is collated.

“We are also putting 100 of them densely spaced every 500 metres in the Waimata Valley where there are mudpools and bubbling mud, to find out more about the mud-plumbing system.”

NZ3D FWI is part of a larger series of projects aimed at helping scientists understand the behaviour of the subduction zone to help minimise the risk posed to communities along the East Coast.

“All of the projects are focused on the geohazards and learning more about them,” Dr Bell said.

“What we learn here is important because we can compare with other data and figure out the true danger of the zone.”

Soundwaves and seismometers

Research vessel Marcus Langseth will be working off the Coast producing soundwaves and another ship will be installing underwater seismometers.

“We will collect seismic reflection data so the ship will produce soundwaves, which will travel through the subduction zone and reflect off boundaries between different types of rock and sediment,” Dr Bell said.

“These soundwaves will be detected by some of the seismometers on land and will show what the rock layers look like under water.”

The JOIDES Resolution, a drilling research vessel, is also offshore drilling more than 1.5km into the sea floor to find out more about underwater landslides and the Hikurangi subduction zone.

“In March next year I am coming back to New Zealand to go on board the JOIDES Resolution," Dr Bell said.

“We will install two earthquake observatories that will stay in place for up to a decade.”

The scientists are enjoying their stay in Gisborne.

RESEARCH ship the JOIDES (Joint Oceanographic Institutes for Deep Earth Sampling) Resolution left for Lyttelton Harbour earlier this week after being stationed off the coast of Gisborne since December 15.

“We’ve recovered 190 metres of sediment core from the seafloor in the Tuaheni Landslide Complex,” said Erin Todd on board educator on the JOIDES Resolution.

“Three holes were logged while drilled (LWD) to measure physical properties of the shallow seafloor sediments.

“The depths of the LWD holes are between 600 and 750 metres below the seafloor and the measurements will be used to guide coring operations in an upcoming IODP (International Ocean Discovery Programme) expedition in March and April.”

The JOIDES Resolution is undertaking scientific drilling research to learn more about the processes that drive large earthquakes and tsunami.

New Zealand’s participation in this expedition and in the IODP is supported by government scientific research funds.

  • East Coast LAB is a collaborative project that brings together scientists, emergency managers, experts and stakeholders across the East Coast to make it easy and exciting to learn more about the natural hazards that affect the region.

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