A new video shows the devastation caused as a giant megathrust earthquake strikes off New Zealand, swamping the east coast with 12-metre waves.
University of California research geophysicist Steven Ward has created a computer simulation showing the moment of impact.
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"Scientists now think that a major tsunami earthquake will someday strike the east coast of New Zealand," he says.
"This is a physics-based simulation of that wave."
Megathrust quakes happen when one tectonic plate is suddenly forced up over another. The Hikurangi margin marks where the Indo-Australian and Pacific plates collide.
Because it runs along the eastern coast of the North Island just offshore, a megathrust quake there could create a massive tsunami like that which swamped Sendai in Japan in 2011.
An initial pile of water would rise in the sea, before heading towards land. Waves would strike within 10 minutes. And within an hour, a five to 12-metre tsumani would strike almost the entire east coast of the North Island.
A 2013 study found that, in a worst case scenario, an 8.9-magnitude quake on the Hikurangi margin could cause 3350 deaths, 7000 injuries and lead to $13 billion of damage in Wellington alone.
And we could be overdue for another one.
The current seismic model estimates 8.1-8.3 types of mega quakes occur every 500 to 1000 years.
Our last quakes occurred between 520 to 470 years ago, and the other 880 to 800 years ago.
GNS scientists say the Christchurch, Kaikōura and Fiordland quakes would pale in comparison to one that could strike the Hikurangi margin.
"We need to think Japan 2011 basically, because if our whole plate boundary ruptured it would be a magnitude 9.0 earthquake," GNS scientist Ursula Cochran told Fairfax in 2017.
"One thing about reflecting on from the Kaikōura earthquake is we don't want people to think this is the big one."
The Sendai quake of 2011 was a megathrust quake measuring about 9.1. It and the subsequent tsunami killed nearly 16,000 people. The 2004 Boxing Day quake, also a megathrust, measured 9.3, killed as many as 280,000 people and literally shook the planet.
Other megathrust quakes include the one which hit Chile in 2010 measuring 8.8 and the biggest quake ever recorded - a 9.5 which shook the South American country in 1960.
Civil Defence's tsunami safety tips
The Ministry of Civil Defence and Emergency Management (MCDEM) warns the tsunami would be a "genuine safety risk" - and urges New Zealanders to be prepared.
It has provided advice on how to protect yourself from a tsunami.
"If you are near the coast and feel an earthquake that is LONG or STRONG: GET GONE," it warns.
"Do not wait for official warnings. For a local source tsunami which could arrive in minutes, there won’t be time for an official warning. It is important to recognise the natural warning signs and act quickly.
"Move immediately to the nearest high ground, or as far inland as you can. Walk or bike if possible."
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