Quake warning devices being put on sea floor

OLIVIA WANNAN
Last updated 05:00 12/05/2014
Dr Stuart Henrys
MARGARET LOW/GNS SCIENCE

TO THE DEPTHS:  Voyage co-leader Dr Stuart Henrys, of GNS Science, with some of the 32 ocean bottom seismometers to be deployed off Poverty Bay.

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The underwater tremor of one of the country's most threatening faults will be unravelled for the first time, with the help of some big orange balls.

GNS Science will be placing the new instruments, known as seismometers, under the ocean on the Hikurangi Subduction Zone this week, starting 25km east of Gisborne.

It is believed this area, where the Pacific tectonic plate is forced below the Australian plate, could be capable of generating a magnitude-9 earthquake, similar to the one that caused Japan's devastating quake and tsunami in 2011.

GNS seismologist Dr Bill Fry said such an earthquake off Gisborne would produce damaging shaking throughout much of New Zealand, including Wellington, as well as a tsunami that would hit most of the country.

The seismometers, some weighing up to 200kg, will spend a year underwater capturing hundreds of small seismic tremors that land-based instruments are unable to properly measure.

They will also monitor "slow-slip" earthquakes, fault movements that take place over weeks or months, rather than the seconds in felt earthquakes, Fry said.

Highly sensitive pressure recorders on the instruments meant they could pick up vertical movements as small as 5mm. The devices will store their data on-board, and scientists will be able to access it when they are retrieved from the ocean floor next year.

Fry said the information would give seismologists "a better appreciation" of the earthquake and tsunami potential of the undersea fault system.

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- The Dominion Post

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