Seismic research is breaking new ground in Southland — uncovering tremors happening 30km below Earth’s surface.
Joint research from the University of Otago and the Natural Hazards Commission (NHC) has recorded earthquakes happening in Southland at twice the depth of those across New Zealand.
Lead researcher Jack Williams said while the report was still being peer-reviewed, he hoped it could guide future science.
‘‘Southland is a gap in our understanding of New Zealand’s faults, but that doesn’t mean they aren’t there and can’t cause damage,’’ he said.
Scientists buried 19 seismometers across Southland and southwest Otago, which measured ground vibrations for a year.
Dr Williams said he was struck by the depth at which the earthquakes were happening across the region.
‘‘If you think of plasticine, when it’s cold and you try to tear it apart, it fractures and breaks. But if you rub it and warm it up a bit, it’s a lot more ductile. The Earth’s crust is similar.
‘‘Near the surface where it’s cold, earthquakes deform the crust by fracturing and rupturing it, but the deeper down you go, the warmer it is and the more ductile the crust becomes.
‘‘There’s kind of a maximum depth that we observe earthquakes and that’s typically about 15 kilometres or so.’’
However, the crust under Southland was rich in strong, brittle iron, which meant an earthquake’s maximum depth could be up 30km deep.
‘‘You’ve kind of got this, like, extra layer of earthquakes going on in Southland … This is pretty unusual anywhere on the Earth’s continents,’’ he said.
‘‘That’s our theory anyway.’’
NHC head of research Natalie Balfour said while research generally focused on regions with high seismic hazard, earthquakes could happen anywhere in New Zealand without warning.
‘‘Areas that are low seismic hazard — it doesn’t necessarily mean that they’re low-risk.
‘‘Hopefully, one day we’ll be able to say a bit more about the potential of those [larger] earthquakes to occur.’’
She hoped the research would encourage people in traditionally low seismic regions to prepare for earthquakes.
‘‘No matter where they are in New Zealand, [people] do understand that earthquakes can occur but perhaps they think ‘it’s less likely to occur where we are’.’’
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