Home / News and Events / Media Releases / Japan tectonic study has implications for NZ - 11/02/2013

Japan tectonic study has implications for NZ - 11/02/2013

An investigation of the plate boundary fault off the east coast of Japan that caused the magnitude 9.0 quake and tsunami in March 2011 has implications for New Zealand, according to an Otago University scientist who contributed to the study.

The IODP drill ship Chikyu  which set a new record in scientific drilling by drilling a borehole 850m below the seafloor in water depths of 6900m

The IODP drill ship Chikyu which set a new record in scientific drilling by drilling a borehole 850m below the seafloor in water depths of 6900m

The investigation, which involved retrieving drill cores from deep under the Pacific Ocean, showed that the massive earthquake released nearly all of the stress that had built up along the plate boundary in that region.

This is unusual, as scientists previously thought that subduction faults release only a portion of their accumulated stress during a large earthquake.

Results of the international study were published in the journal Science this week. The large amount of stress release has helped to explain the 50m horizontal slip on the fault, the longest ever recorded on a seafloor fault.

Geologist Virginia Toy of Otago University, said the findings were significant because most earthquake faults only release a small portion (typically 10%) of the stress in the crust around them, compared to nearly 100% as in this case.

"Also, such a high proportion of stress was probably released because the fault materials were particularly frictionally weak or slippery."

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We need to be prepared for the possibility that these subduction zones will generate larger earthquakes and larger tsunamis than previously thought.

Dr Virgina Toy

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Dr Toy said the results suggested that subduction zone faults in other locations, including around New Zealand, should be more carefully examined.

“New Zealand has so much of its coastline exposed to the Pacific Ocean, which is ringed by subduction zones, for example in Tonga-Kermadec, Hikurangi off the east coast of the North Island, and Chile.

“We need to be prepared for the possibility that these subduction zones will generate larger earthquakes and larger tsunamis than previously thought.”

The expedition, which took place in mid-2012, was carried out on the scientific drilling ship Chikyu, which is operated by the Integrated Ocean Drilling Program (IODP).

The ship drilled several deep holes about 220km east of Japan in water depths of nearly 7000m. Instruments were inserted into one of the boreholes enabling scientists to obtain valuable information about residual heat, stress, fluid and rock properties, and other factors related to megathrust earthquakes.

Dr Toy’s participation was possible through New Zealand's membership of the IODP as part of the Australian-NZ IODP Consortium - a group made up of universities and research institutions from both nations.

The expedition set new milestones in scientific drilling by drilling a borehole to 850m below the seafloor in water depths of 6900m.

Future IODP expeditions are planned for east of Gisborne where scientists hope to carry out similar drilling and monitoring of the Hikurangi margin – an area where the Pacific Plate is subducting under the Australian Plate.

By drilling in this region, scientists hope to better understand the subduction processes and the earthquake-generating mechanisms of this area.

The project is likely to involve an international team of scientists. They hope to drill a series of up to five deep boreholes into the seabed, to investigate slow-slip earthquake events which occur in the Poverty Bay region every 12 to 18 months. The proposed drilling transect is a straight line with the holes to be drilled at spaced intervals ranging from 30km to 100km from the coast.

The first phase of what scientists are calling the Hikurangi Margin IODP expedition which has not been scheduled, but is likely to take place in 2015/16 and will use the US-operated ship JOIDES Resolution.

For further information on New Zealand's participation in IODP visit DrillNZ .

A media release on the Science publication is available here:

The US-operated IODP scientific drilling ship JOIDES Resolution  which last visited New Zealand in late 2009 is likely to return in  2014 or 2015 to drill several deep boreholes off the coast of Gisborne to investigate the Hikurangi subduction zone. Photo: Margaret Low, GNS Science.

The US-operated IODP scientific drilling ship JOIDES Resolution which last visited New Zealand in late 2009 is likely to return in 2015/16 to drill several deep boreholes off the coast of Gisborne to investigate the Hikurangi subduction zone. Photo: Margaret Low, GNS Science.