By John Kerr 20/11/2016

The tsunami generated by last week’s 7.8 earthquake was not expected as the quake was initially centered on land, not offfshore.

In the week since the quake there has been a lot of public debate over the efficacy of New Zealand’s national and local tsunami warning systems. The Science Media Centre has collated much of the coverage here.

A key point of confusion related to the initial announcement from the Ministry of Civil Defence and Emergency Management (MCDEM), just half an hour after the quake, that there was no tsunami threat.

In the latest MCDEM media briefing Ken Gledhill, Director of GeoNet, said the fact that the Hanmer quake was initially centred on land but triggered faults extending offshore was one reason why there had been some initial confusion.

“There will always be lessons to be learned. But this was a complex earthquake,” he said.

“It was actually responded to incredibly quickly by a duty person and the processes were followed really well.

“The tsunami turned out to be a surprise and it wasn’t a surprise just for us. My international colleagues… they had the same issue: large, on-land earthquakes to not normally cause tsunami. I don’t think with the current set up we could really do much better.

“Technological solutions are coming along which will help us a lot and we should be looking at those very seriously,” he added.

Watch the full briefing below:

Text message warning system

In the last day media have reported that the government is investigating a nation-wide text warning system. The New Zealand Herald reports:

PM John Key says the Government expects to announce measures for a national disaster warning system which will send out an alert to every cellphone in the country.

Key said the Government had been working on it for some time prior to the most recent spate of earthquakes and there was money set aside in the Budget for a national alerting system in disasters, similar to those used in other countries.

“My understanding was that it was certainly turning out to be more expensive than we thought and we’ve been shopping around trying to see if we can get a better alternative.

“There is no doubt that where we will be going is national alerting. It doesn’t matter if your cellphone is on or not, it’s not a matter of whether they know about your cellphone or not, it just blasts a message out to everyone. That’s a strong positive.”

However, he said when it came to tsunami people in low lying areas should move to higher ground immediately after a long, strong earthquake rather than wait.

Earthquakes: the best tsunami warning system

“If you are at the coast, and feel a long or strong earthquake, be gone.”

This advice, provided by Dr.Gledhill on the day of the 7.8 quake that rocked central New Zealand, remains the best advice on what to do in a potential tsunami situation after an earthquake.

Some tsunami may be generated by offshore quakes so far away we don’t feel them. In these situations, there needs to be robust systems in place to alert everyone in an at risk area to evacuate. MCDEM, drawing on information from GeoNet and the Pacific Tsunami Warning Centre located in Hawaii, are responsible for disseminating official warnings through their National Warning System, which includes broadcasters and local civil defence groups.

The National Warning System covers hazards such as tsunami
The national warning system. From Section 25 of the Guide to the National CDEM Plan.

But when a quake is closer to home there may not be time to get an alert out. The official line from MCDEM goes like this:

A tsunami generated in conjunction with a nearby large earthquake or undersea landslide may not provide sufficient time to implement official warning procedures.

Persons in coastal areas who:

  • experience strong earthquakes (hard to stand up)
  • experience weak earthquakes lasting for a minute or more
  • observe strange sea behaviour such as the sea level suddenly rising and falling, or hear the sea making loud and unusual noises or roaring like a jet engine

should not wait for an official warning.  Instead, let the natural signs be the warning. They must take immediate action to evacuate predetermined evacuation zones, or in the absence of predetermined evacuation zones, go to high ground or go inland.

If you are interested in learning more about how MCDEM manages national tsunami warnings, have a look the recently updated National Tsunami Advisory and Warning Plan.