New Zealand Tsunami Sources and Warnings – TVNZ Breakfast


Yesterday civil-defense sent out a
warning that we may see some strong sea surges following a massive earthquake
off the coast of Alaska, but then Civil Defense downplayed the threat of an actual tsunami, so exactly where in the world does an
earthuake have to strike for us to be really worried about a giant wave and how long would we have to get to safety? Joining us is Graham Leonard, an expertin hazard mapping at GNS Science. Tena koe, good morning. Good morning Jack. We want to work through three main areas of concern this morning, and I thought you might be able to give us a bit of an insider’s explanation on exactly how this works for when we should and shouldn’t be concerned about tsunamis and we might start with the outer regions this morning. We consider the whole rim of the Pacific as a potential source for
tsunami but we break it down into distant, regional, and local sources so starting with distant sources,
that sources more than three hours of tsunami travel time away from New Zealand. We’re worried about tsunami potentially from earthquakes along South America, Central America, off of Canada, Alaska and Japan for that source, and in that case it’s usually 12 or more hours of warning time, definitely more than 3 hours. in that case we have an official warning system with Civil Defense in place to tell people when they need to evacuate. and so for a distance source such as the earthquake areas you just mentioned, what is the threat of tsunami?
it’s pretty minimal right? Well it depends on the place. The the size of the tsunami we might get depends on three things: how much of the sea floor is deformed by the earthquake, how far away it is, and what the orientation of that seafloor is to New Zealand. So the Alaskan earthquake a couple of nights ago, it’s a long way away, it was less than magnitude 8, and the orientation wasn’t quite right, so we didn’t get much of a tsunami from it but a different earthquake up there – any one of those things a bit different, we could get a bigger tsunami, and somewhere a bit
closer with a different orientation like Chile or especially Peru, we could get
quite a substantial tsunami. Okay, that’s interesting I wonder with the Alaskan situation too, if you can say there’s been a big earthquake off the coast of Alaska, well between us and Alaska there’s a little bit, we’ll wait and see if anything happens to Fiji, if nothing happens to Fiji we should be alright? Yeah well we’ve got access to deep
ocean dart buoys which the tsunami travels over. The weight of the water activates this pressure sensor and we can actually see the signal coming across it so for those distant sources
that’s one of those early signs. We can calibrate how big the tsunami might be based on what the signal coming from those dart buoys is. Right, let’s move a little closer to New
Zealand. And you call this the regional area. Yeah so we consider the area within 1-3 hours of travel time to New Zealand as the regional source area. and most of the concern there is the area up the Kermadec Islands, up through to Tonga and Samoa. So if we’ve got an earthquake up in that area, it might take 1-3 hours to get here. Again we’ve got enhanced warning arrangements in place with Civil Defense. So you might feel a long the earthquake in that case but the goal is to give official warnings
through official channels for that one. So you should start getting a little more
concerned if we hear of a really big earthquake off the coast of Tonga or
somewhere like that. Let’s talk local sources now, these are the earthquakes that really have the potential to cause tsunami. It’s the same sort of source it’s this plate boundary all the way around the Pacific, but the bit of it that’s offshore from Kaikoura, past Wellington, past Napier, up through East Cape Tsunami from there are less than an hour
away, they could just be minutes away depending on where you are. So in that case it’s all about ‘Long, strong, get gone’. So if the earthquakes longer than a minute
or it’s strong enough that it’s hard to stand up you need to evacuate immediately to high ground
or inland. Don’t wait for any official warning. The fastest and best warning is that earthquake itself. and because it’s so close, that’s also the source where we could get the biggest
wave. Right, an earthquake lasting more than a minute. Now for people who went through the Christchurch earthquakes, they said they seemed to last for ages but it’s really hard to have a perspective on time when you’re in the moment. Yeah so in Wellington where I am now, we
felt the Kaikoura earthquake for at least a minute whereas actually in Christchurch those quakes we’re less than a minute But yeah they feel like forever, for sure. Okay hey that is so interesting,
thanks for your time and your help this morning.

8 thoughts on “New Zealand Tsunami Sources and Warnings – TVNZ Breakfast

  1. I think South Auckland sits on a tsunami plaini, and will probably (soon) be the site of the largest loss of life, by tsunami, that the world has ever seen

  2. What if the first smaller wave knocks out the sencers, then the biger waves aren't detected.

  3. We know from numerous occasions some agencies downgrade some earthquakes to ?.9 to keep their averages but thats at least only a 10th magnitude of what it actualy is. And then there's the USGS who choses not to show some earthquakes for political reasons, ($).
    We can't be relying on other agencies buoy reports to be accurate or on time when they are prepared to put they're own political interests ahead of kiwis.

  4. Did you know New Zealand and Australia use to be a country together? And guess what? You know where the little island is on Australia? New Zealand use to be there

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