Dr Virginia Toy
Research into the power of a devastating tsunami in Japan
in 2011 shows that an earthquake off the coast of New Zealand
could produce a larger tsunami than previously thought, a
University of Otago scientist says.
The study, published in Science, showed the magnitude 9
Tohoku-Oki earthquake in Japan released nearly all the stress
built up along the plate boundary, moving the sea floor
nearly 50m. The quake and following tsunami resulted in more
than 15,000 deaths.
Otago University Department of Geology scientist Dr Virginia
Toy, who took part in the study, said the finding was
significant as earthquakes typically only released about 10%
of the stress in the crust.
''The research confirms some of our suspicions based on the
Tohoku-Oki event that subduction zones are capable of
generating larger tsunamis than we expected.''
This had significant implications for New Zealand as our
coastline was ringed by similar ''subduction zones'' such as
Tonga-Kermadec, the Hikurangi Trench and Chile.
The research showed a tsunami in New Zealand could be larger
than previously expected.
''It ups the ante a little bit and says let's be even more
cautious than we were previously,'' Dr Toy said.
It also served as a reminder for people to take tsunami
warnings - such as the one prompted by the magnitude 8 quake
in the Solomon Islands on Wednesday - seriously.
Just because warnings were often not followed by big waves
did not mean people should become ''blase''.
''It's a bit like when the MetService says snow is forecast.
It doesn't always snow, but at least people have put their
In order to test their hypothesis, the study authors, led by
Weiren Lin from the Kochi Institute for Core Sample Research
in Japan, drilled into the fault to test the strength of the
surface, finding that it was ''frictionally weak''.
''Such a high proportion of stress was probably released
because the fault materials were particularly frictionally
weak or slippery,'' Dr Toy said. There was a need for similar
research to see if other subduction zone faults had a similar
make-up, she said.
''It indicates to me that we need to do similar kinds of
drilling projects in places like the Hikurangi Trench [off
the coast of the North Island] to see if we are dealing with
''If the materials in the fault planes are similar to those
in the Japan Trench, it is likely they will also be very
frictionally weak and therefore that we can also expect very
large seafloor displacements when they slip.''