Kelvin Berryman of GNS Sciencee explains how the seabed was raised by the recent earthquakes
Parts of New Zealand are sinking at faster rates than others and rising faster, a scientist says.
The just-published tectonic research provides new information about how different parts of New Zealand are either rising or subsiding in relation to the centre of the earth.
Data was collected by GeoNet's GPSrecorders between 2000 and 2015, and the first map has been produced of relative vertical movements of the Earth's surface based on measurements at 189 places across the country.
Analysis of the data shows that parts of New Zealand, like the North Island's east coast, have subsided by as much as 3mm a year for the past 15 years.
This means this region is effectively subjected to a maximum sea level rise of up to 6mm a year, which is twice the global average.
Co-author Professor Tim Stern, of Victoria University's School of Geography, Environment and Earth Sciences, said other parts of New Zealand were rising.
"For example, along parts of the Bay of Plenty coast, the Whanganui coast and south to the Kapiti region, and along the Otago, Westland and Southland coastlines, there are small rises of 1mm per year or less."
This meant sea level rise in these areas would be less than the global average.
"The data also show inland areas of the South Island and the Southern Alps are rising by up to 6mm per year, while in the Rotorua area there is a remarkable subsidence rate of 15 mm per year.
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"Most of these areas of subsidence and uplift can be explained through our knowledge of plate tectonic processes occurring in New Zealand."
Stern said the research was a good start to understanding New Zealand's exposure to sea level rise.
"It is well accepted that global warming is a major factor causing present-day global sea levels to be rising by 2-3mm a year.
"What's less known, however, is that in some places, such as New Zealand, tectonic processes can locally add to land subsidence, whereas elsewhere they act to negate it.
"This new information should be a key input into planning to mitigate coastal erosion and to enhance our resilience to sea level change. In five to 10 years, we will have even more information from the GPS technology to add to this knowledge."
The research, co-authored by Stern and Dr Nicolas Houlie from ETH-Zuric in Switzerland, has been published online in Earth and Planetary Science Letters.
Stern said last week's earthquake and uplift of the Kaikoura-Cape Campbell region is a reminder that that earthquake events can suddenly reverse the decades-long subsidence seen in parts of eastern North Island.
