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$20 million ocean floor “earthquake observatory”

Joides

Republished from the Gisborne Herald 

Scientists plan to install undersea sensors east of Gisborne will lead to more accurate information on undersea quakes.

In 2018 New Zealand will become one of only a few countries in the world to have a sub-ocean floor “earthquake observatory” off its coast through the 26-nation International Ocean Discovery Program (IODP).

It will involve a research ship drilling three holes up to 1.5km deep in the sea floor in different parts of the overlying Australian tectonic plate, about 40km east of Gisborne.

Expedition leader and GNS Science geophysicist Laura Wallace said the $20 million project’s findings would almost certainly have global significance.

“It has the potential to significantly boost the understanding of the mechanics of subduction zone faults and the earthquakes that occur on them,” Dr Wallace said.

The project’s main aim was to improve the understanding of slow-slip or silent earthquakes, which are a feature of the subduction zone east of the North Island.

However, Dr Wallace said after last week’s earthquake northeast of East Cape, there was a case to be made for data from the seafloor instruments to be sent onshore in real time using fibre optic cable.

“A continuous quake-monitoring capability east of the North Island would be enormously helpful in speeding up the analysis and understanding of complex offshore earthquakes that might potentially have generated a tsunami.”

The distances between offshore quake epicentres and land-based seismometers meant it was difficult for New Zealand’s current national network, operated by GeoNet, to quickly resolve the depth, location and magnitude of offshore earthquakes.

“Knowing this kind of information with confidence is crucial to issuing timely tsunami warnings.”

Dr Wallace said the project, which involved 50 scientists, would have multiple benefits in understanding a range of plate boundary phenomena.

The US-based ship, Joides Resolution, would insert a range of instruments into one of the boreholes to make continuous physical and chemical measurements inside the plate boundary zone.

The instruments would stay in place for at least the next decade and would detect any changes due to earthquakes and other types of tectonic events in the region.

The ship would also collect samples of sediment and rock from the drill holes for scientists to analyse.

A key focus for scientists involved in the project would be to learn how the temperatures and pressures at depth, and the types of rocks being subducted, might influence the occurrence of earthquakes and slow-slip events at the subduction zone — where the Pacific plate is being forced under the Australian plate.

Dr Wallace said for the past three years, there had been a “rolling deployment” of seafloor sensors off the Gisborne coast to monitor slow-slip activity and earthquakes on the Hikurangi subduction zone, but those had to be recovered by ship each year.

“These seafloor instruments have given us tremendous insights into the workings of this complex plate boundary fault zone but the information is always retrospective.”

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