The magnitude 7.8 'Kaikoura earthquake' that hit New Zealand in November 2016 has caused the North and South islands to move closer to each other, scientists from GNS Science have found. The earthquake, which caused rupturing of at least 25 fault lines across the country, has also caused the city of Nelson, at the top of the South Island, to sink.
The margins are negligible, however, as the gap between the North and South islands has narrowed by just 35 centimetres, while Nelson city has sunk by up to 20 millimetres.
The Kaikoura earthquake was one of the most complicated earthquakes in the world. Geologists believe such events occur only once every 5,000-10,000 years. The epicentre of the quake was located near Waiau, North Canterbury; from the, it raced northwards - travelling about 2 kilometres per second and ending up off Cape Campbell in Marlborough. The quake covered 174 kilometres in about 74 seconds.
The massive energy released had an immediate impact on the landscape of North Canterbury and Marlborough. Some parts of the Marlborough coast were lifted by more than 6 metres, and dropped more than 2 metres at others. Thousands of landslides were also recorded over an area of about 10,000 square kilometres.
After the main shock, scientists from GNS Science (formerly the Institute of Geological and Nuclear Sciences) and the University of Otago installed GPS sensors across the quake zone to monitor the impact of the quake. They found that the unsettled fault lines since the main shock have nudged the southern landmass further north.
The data shows that Cape Campbell has moved the most in the past two years, and is now 35 centimetres closer to Wellington than before the earthquake.
Blenheim slid 15 centimetres further northeast, while Kaikoura is now 15 centimetres further east.
Sigrun Hreinsdottir, a scientist at GNS Science, says it is difficult to identify the specific fault line responsible for the post-quake creep as so many were ruptured after the quake.
"In reality we are having all this creeping going on and the question is, which [fault] is the dominant factor?" she said.
Hreinsdottir added that Nelson had fractionally slumped and is sinking by 10 to 20 millimetres.
"It's not a huge amount but it is observable at our sites," she added.
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