Jamie Morton

Jamie Morton is science reporter at the NZ Herald.

Scientists deploy devices to help study 'silent earthquakes'

32 instruments will be deployed on the sea floor near Poverty Bay to help scientists get a better understanding of the quake risk there. Photo / GNS
32 instruments will be deployed on the sea floor near Poverty Bay to help scientists get a better understanding of the quake risk there. Photo / GNS

Quake-recording instruments to be deployed on the seabed near Poverty Bay will give scientists a deeper insight into earthquake and tsunami risk in one of the country's biggest natural disaster risk zones.

More than 30 instruments belonging to the US and Japan will be dropped around the area over the next two weeks and will remain in place for a year, recording earthquakes and any upward or downward movement of the seafloor.

The project is designed to give valuable insights into the earthquake and tsunami potential of the Hikurangi subduction zone, which lies to the east of Gisborne several kilometres below the seafloor and is a meeting point of the Australian and Pacific plates.

It is the largest-ever deployment of seafloor instruments specifically targeted at the study of what are known as slow-slip events, or "silent earthquakes" - a rare phenomenon which occur over a matter of weeks to months instead of seconds.

Occurring at roughly 18 month intervals around Poverty Bay, these earthquakes involve parts of the region moving eastward by up to 2cm over one or two weeks, and if the land movement occurred in seconds rather than weeks, like a normal earthquake, it would be equivalent to a magnitude 6 to 7 jolt.

GNS Science seismologist Bill Fry said the study would lead to a better appreciation of the earthquake and tsunami potential of this undersea fault system.

"Subduction zones, such as the one offshore the North Island, are responsible for generating the world's largest earthquakes, sometimes called megathrust quakes."

Devastating examples were the 9.1 Sumatran quake (Boxing Day tsunami) in 2004 and the 9.0 Tohoku quake in Japan in 2011, and seismologists believe the Hikurangi subduction zone is capable of a 9.0 megathrust quake.

- NZ Herald

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