An 8.4 magnitude quake off the eastern coast of New Zealand could release 2,000 times more energy than the 2011 Christchurch earthquake, and could cause a "megathrust" earthquake.
The potential risk comes from the Hikurangi subduction zone, a massive fault line running from Marlborough and right past the East Coast where the Pacific and Australian tectonic plates collide. It is potentially the largest source of earthquake and tsunami hazards in New Zealand.
According to a report in New Zealand Herald, that cites GNS earthquake geologist Kate Clark, scientists in the past 15 years have used global positioning satellites (GPS) to track the movement of land above the subduction zone. This has shown that parts of the zone are "stuck" together and accumulating stress that will eventually be released in a large earthquake.
Dr Clark adds that a megathrust earthquake on the Hikurangi subduction zone is likely to be quite different from the Christchurch and Kaikoura earthquakes. A megathrust quake is likely to generate ground shaking for much longer (minutes) and over a wider area (much of New Zealand) than the 2010-2011 Christchurch and the 2016 Kaikoura earthquakes. The intensity of shaking is likely to be different too, depending on how deep and where the megathrust earthquake occurs. The Kaikoura earthquake generated a tsunami but a megathrust earthquake is likely to generate a larger tsunami that impacts a wider region.