What lies beneath

International team launch Hikurangi subduction zone project

International team launch Hikurangi subduction zone project

SEEING IN 3D: GNS Science scientists Dan Bassett, Dan Barker, and Katie Jacobs with some of the recording instruments that will be placed on the seafloor off the East Coast as part of the project to study the Hikurangi subduction zone. The instruments are on loan from Japan for the duration of the project.

Picture by Margaret Low, GNS Science.
Summary of Hikurangi subduction project

AN international team of scientists have started deploying hundreds of recording instruments here in a bid to learn more about a potential “megathrust” earthquake threat posed by the way tectonic plates are acting beneath the East Coast. Seismometers deployed on land and offshore will record earthquakes and slow-slip events that occur in an area known as the Hikurangi subduction zone, which marks the boundary of the Pacific and Australian tectonic plates.

Subduction zones like Hikurangi, which is at one point 50 kilometres off the Gisborne coast, produce the planet’s biggest and deadliest earthquakes — also referred to as megathrust earthquakes — as well as devastating tsunami.

It is arguably New Zealand’s most significant active fault and is capable of generating a magnitude 8.5 earthquake that, in addition to widespread ground shaking, is also likely to produce a tsunami, coastal uplift and subsidence, landslides and liquefaction.

New Zealand project leader Dr Stuart Henrys, of GNS Science, said scientists from New Zealand, Japan, the United States and the United Kingdom were involved in the project, which was aimed at better understanding the potential threat to New Zealand from the Hikurangi subduction zone.

The project, called Seismogenesis at Hikurangi Integrated Research Experiment (see graphic), or SHIRE for short, is funded by the US National Science Foundation and the Ministry of Business, Innovation and Employment. The offshore section of the project will begin later this month, with NIWA’s research ship Tangaroa due to lower 100 specially made seismometers on to the seafloor in a grid pattern running from offshore Wairarapa north to east of Ruatoria.

In addition to the seafloor instruments, scientists have started to deploy more than 200 land-based seismic instruments across the Raukumara Peninsula. The seafloor and land-based instruments record echoes from within the Earth from both naturally occurring earthquakes and acoustic signals generated by a US research ship, Marcus Langseth, which will be positioned off the East Coast. This will enable scientists to create images of the plate boundary fault zone underneath the sea and beneath the land.

The CAT scan-like images will show the structure of the Earth’s crust to a depth of about 30km. In most places over the study area the images will be two-dimensional, or like slices through the Earth. However, a more intensive survey area northeast of Gisborne will produce three-dimensional images of the plate boundary collision zone.

The images will show the position of the two tectonic plates and also help scientists determine the physical properties of the various rock layers that make up the subduction zone. The nature of the rock material on the grinding surface of each plate affects how the two plates move past each other.

Using this information, scientists can learn more about how the plates are locked together at numerous points along the subduction zone. Dr Henrys says the data will help the understanding of why different areas of the plate boundary are behaving so differently. Some parts of the plate interface slide past each other every year or so in events called slow earthquakes. Other parts appear to be stuck fast and are storing energy for a future large earthquake.

A most pressing question

Lead US investigator from the University of Texas, Harm Van Avendonk, says the project will produce detailed images of the entire fault system across this part of the North Island.

“A better understanding of what causes the marked differences in tectonic behaviour on this plate boundary will help New Zealand government agencies in their efforts to reduce the danger posed by earthquakes and tsunami in this area,” Dr Van Avendonk said. “What makes subduction zones rupture in huge, tsunami-generating earthquakes is one of the most pressing questions facing Earth scientists today.”

Best place in the world

Dr Henrys says the more intensive study zone northeast of Gisborne is an exciting prospect as it should provide the best images yet, anywhere in the world, of the zone where slow-motion earthquakes are known to occur repeatedly. Scientists regard the area off the East Coast as the best place in the world to study and understand the phenomenon of slow-motion earthquakes.

“This is because it is more accessible and shallower than other subduction zones around the world, which are typically further from shore.”

Dr Henrys added that the marine seismic reflection system being used in this project involves releasing compressed air quickly into the water with sensors towed behind the ship picking up “echoes” from different rock types in the upper layers of the Earth’s crust.

Minimal disruption to marine life

The project has got all the necessary consents and approvals from various agencies including the Department of Conservation and EPA, and will not involve any “fracking”. Specialist observers will also be used to ensure minimal disruption to marine mammals.

“There is a full system in place in order to mitigate the effects against marine mammals. For instance, if a marine mammal is sighted in the zone then immediately the “guns” will shut off until the marine mammal moves out of the zone.”

AN international team of scientists have started deploying hundreds of recording instruments here in a bid to learn more about a potential “megathrust” earthquake threat posed by the way tectonic plates are acting beneath the East Coast. Seismometers deployed on land and offshore will record earthquakes and slow-slip events that occur in an area known as the Hikurangi subduction zone, which marks the boundary of the Pacific and Australian tectonic plates.

Subduction zones like Hikurangi, which is at one point 50 kilometres off the Gisborne coast, produce the planet’s biggest and deadliest earthquakes — also referred to as megathrust earthquakes — as well as devastating tsunami.

It is arguably New Zealand’s most significant active fault and is capable of generating a magnitude 8.5 earthquake that, in addition to widespread ground shaking, is also likely to produce a tsunami, coastal uplift and subsidence, landslides and liquefaction.

New Zealand project leader Dr Stuart Henrys, of GNS Science, said scientists from New Zealand, Japan, the United States and the United Kingdom were involved in the project, which was aimed at better understanding the potential threat to New Zealand from the Hikurangi subduction zone.

The project, called Seismogenesis at Hikurangi Integrated Research Experiment (see graphic), or SHIRE for short, is funded by the US National Science Foundation and the Ministry of Business, Innovation and Employment. The offshore section of the project will begin later this month, with NIWA’s research ship Tangaroa due to lower 100 specially made seismometers on to the seafloor in a grid pattern running from offshore Wairarapa north to east of Ruatoria.

In addition to the seafloor instruments, scientists have started to deploy more than 200 land-based seismic instruments across the Raukumara Peninsula. The seafloor and land-based instruments record echoes from within the Earth from both naturally occurring earthquakes and acoustic signals generated by a US research ship, Marcus Langseth, which will be positioned off the East Coast. This will enable scientists to create images of the plate boundary fault zone underneath the sea and beneath the land.

The CAT scan-like images will show the structure of the Earth’s crust to a depth of about 30km. In most places over the study area the images will be two-dimensional, or like slices through the Earth. However, a more intensive survey area northeast of Gisborne will produce three-dimensional images of the plate boundary collision zone.

The images will show the position of the two tectonic plates and also help scientists determine the physical properties of the various rock layers that make up the subduction zone. The nature of the rock material on the grinding surface of each plate affects how the two plates move past each other.

Using this information, scientists can learn more about how the plates are locked together at numerous points along the subduction zone. Dr Henrys says the data will help the understanding of why different areas of the plate boundary are behaving so differently. Some parts of the plate interface slide past each other every year or so in events called slow earthquakes. Other parts appear to be stuck fast and are storing energy for a future large earthquake.

A most pressing question

Lead US investigator from the University of Texas, Harm Van Avendonk, says the project will produce detailed images of the entire fault system across this part of the North Island.

“A better understanding of what causes the marked differences in tectonic behaviour on this plate boundary will help New Zealand government agencies in their efforts to reduce the danger posed by earthquakes and tsunami in this area,” Dr Van Avendonk said. “What makes subduction zones rupture in huge, tsunami-generating earthquakes is one of the most pressing questions facing Earth scientists today.”

Best place in the world

Dr Henrys says the more intensive study zone northeast of Gisborne is an exciting prospect as it should provide the best images yet, anywhere in the world, of the zone where slow-motion earthquakes are known to occur repeatedly. Scientists regard the area off the East Coast as the best place in the world to study and understand the phenomenon of slow-motion earthquakes.

“This is because it is more accessible and shallower than other subduction zones around the world, which are typically further from shore.”

Dr Henrys added that the marine seismic reflection system being used in this project involves releasing compressed air quickly into the water with sensors towed behind the ship picking up “echoes” from different rock types in the upper layers of the Earth’s crust.

Minimal disruption to marine life

The project has got all the necessary consents and approvals from various agencies including the Department of Conservation and EPA, and will not involve any “fracking”. Specialist observers will also be used to ensure minimal disruption to marine mammals.

“There is a full system in place in order to mitigate the effects against marine mammals. For instance, if a marine mammal is sighted in the zone then immediately the “guns” will shut off until the marine mammal moves out of the zone.”

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