Home / News and Events / Media Releases / Japanese plate boundary findings have relevance to NZ - 20/06/2017

Japanese plate boundary findings have relevance to NZ - 20/06/2017

Scientists have found that up to 50% of tectonic energy at a subduction zone east of Japan is released during slow earthquakes which occur under the seabed at this location every 12 to 18 months.

The findings come from information derived from two boreholes 11km apart and drilled into the ocean floor at the Nankai Trough subduction zone in 2009 and 2010.  

The boreholes were packed with monitoring instruments which have revealed new information about the earthquake behaviour of plate boundaries. The boreholes are part of a network of instruments, which includes sensors on the seafloor. 

Until this scientific drilling project, scientists were unsure how much of the energy in shallow subduction zones was dissipated by slow earthquakes.

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The Nankai Trough results are important for understanding the risk of large earthquakes and tsunamis generated at offshore plate boundary zones worldwide

Dr Laura Wallace

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The Nankai Trough research, which was led by Japanese and American researchers, and included geophysicist Dr Laura Wallace of GNS Science, was published last week in the prestigious journal Science. 

The Japanese project has direct parallels with New Zealand’s Hikurangi Margin east of the North Island, which will be probed with similar exploratory boreholes off the Gisborne coast in 2018. Slow-slip earthquakes also occur east of Gisborne every 12 to 18 months.

The Japanese boreholes were drilled by the International Ocean Discovery Program (IODP), which will also be drilling boreholes and installing instruments inside them about 60km off the Gisborne coast in 2018 using the US research ship JOIDES Resolution.

Dr Wallace said that the experience gained with the Nankai Trough project was directly applicable to the Hikurangi subduction zone project in 2018.

She said the Japanese findings underlined the importance of investigations using scientific drilling ships and installing instruments below the seafloor to measure changes in fault and earthquake processes over extended periods of time.

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It might open a new view of what is happening in the plate boundary east of Gisborne. It’s exciting because the project has the potential markedly improve our understanding of shallow subduction zones not just in New Zealand, but internationally as well.

Dr Laura Wallace

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“The Nankai Trough results are important for understanding the risk of large earthquakes and tsunamis generated at offshore plate boundary zones worldwide.”

Leader of the Nankai Trough study, Dr Demian Saffer of Pennsylvania State University, said the 50% or so of tectonic energy not dissipated by periodic slow earthquakes at Nankai remains an outstanding question: it could be taken up by silent creep, but it could also be accumulating for release during the next big earthquake on the subduction zone.

Drs Saffer and Wallace will be co-leading the JOIDES Resolution expedition between March and May in 2018 to install instruments in the boreholes east of Gisborne to investigate slow-slip events that occur on the Hikurangi subduction zone, similar to those at the Nankai Trough.

“The Nankai finding hints that slow-slip earthquakes may reduce tsunami risk by periodically relieving tectonic stress, but it is probably much more complicated than acting as a simple relief valve,” Dr Saffer said.

He said it is too simplistic to conclude that slow-slip events automatically reduce the risk of big quakes and tsunamis, because the research also showed that the slipping part of the subduction interface is capable of storing strain.

Dr Wallace said the findings from the instruments inside the boreholes in the Nankai Trough were unexpected. 

It opened up the possibility that information recorded in the boreholes planned off the Gisborne coast might reveal types of tectonic plate behaviour that had not been observed before.  

“It might open a new view of what is happening in the plate boundary east of Gisborne. It’s exciting because the project has the potential markedly improve our understanding of shallow subduction zones not just in New Zealand, but internationally as well.”

The scientists involved in the Hikurangi subduction zone project are spending this week outlining their research at a series of public meetings in Gisborne, Tolaga Bay and Ruatoria.

Silent earthquakes

Media coverage of this news story
Silent quakes help faults let off steam – The NZ Herald, 20 June 2017
http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11879572

Slow-slip quakes, like those in NZ, can relieve pressure on dangerous faults – Fairfax Media, 20 June 2017
http://www.stuff.co.nz/science/93818290/slowslip-events-like-those-in-nz-can-relieve-pressure-on-dangerous-faults

Scientists explain seismic research – The Gisborne Herald, 20 June 2017
http://gisborneherald.co.nz/localnews/2855200-135/scientists-to-explain-seismic-research