New Zealand would have 45 minutes to prepare for Kermadec tsunami - GNS Science

GNS Science warns we would only have 45 minutes to prepare and evacuate for an oncoming Kermadec tsunami.

New Zealand was shocked awake on Sunday morning after Civil Defence issued a beach and marine tsunami warning following a M7.4 earthquake in the Kermadec Islands region.

Fortunately this was withdrawn just minutes later. However a strong quake swarm continues to thump the ocean northeast of Auckland, aftershocks of the main event.

Speaking to Newshub on Monday, GNS Science duty seismologist Dr John Ristau warns we need to remember large earthquakes can occur at any time.

"It is well known that earthquakes occurring in the Kermadec region have the potential to generate tsunamis," he says.

"Travel time would be affected by the location of the earthquake epicentre. At the southern end of the Kermadec region, it could be as little as 45 minutes. Further north, it would be about two hours.

"The most vulnerable parts would be the parts along the northern coast nearest to the epicentre, ie Northland/Auckland/Bay of Plenty/East Cape. If the earthquake is large enough, the entire coast of New Zealand would be threatened to varying degrees."

Dr Ristau says an earthquake in a similar location would probably need to be in the high M7.0s to produce a tsunami large enough to be a threat to New Zealand.

"Sunday's earthquake did generate a very small tsunami at Raoul Island - about 0.1m at the two tsunami gauges operated by the GeoNet project on the Island," he says.

Why is the Kermadec region so dangerous?


A subduction zone is where two tectonic plates collide, pushing one under the other and causing enormous forces to build up until they're released in an earthquake.

The Kermadec Trench's subduction zone extends from the Hikurangi Plateau, just north of New Zealand, to the north past Raoul Island.

"In the region of Sunday's earthquake it's about 30 percent faster than that of the Hikurangi subduction zone. This means it is subducting at about 55cm each year," Dr Ristau says.

"US Geological Survey figures show that over the past 10 years, there were 70 quakes of M6 and above in the Kermadec-Tonga Trench. This is more active than the New Zealand mainland, but less active than regions such as Japan and Papua New Guinea."

How can we stay safe?


"Distant earthquakes may not be widely felt here in New Zealand, so it's important that people know the correct actions to take and how to stay informed - via radio, Emergency Mobile Alerts, social media, and the Ministry of Civil Defence and Emergency Management website," Dr Ristau says.

"Make sure you follow all Civil Defence instructions, and if a warning is issued, get to higher ground immediately. You can check out Civil Defence's website for tsunami safety tips.

"How will you know to evacuate? If you are near the coast and feel an earthquake that is long or strong - get gone. Don't wait for an official warning. Get to higher ground immediately. Walking or biking is the best mode of transport to avoid road congestion."


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