Forecasting New Zealand’s seismic apocalypse

This weekend’s tragedy on Japan’s Mount Ontake reminds us that life around the Pacific ‘rim of fire’ is often risky.

That string of tectonic plate collisions stretches around the whole circumference of the Pacific and has shaped life in many ways. It was cause of the 2011 tsunami that devastated eastern Japan. It gave the US Yellowstone. It provokes earthquakes. It has also shaped my home country, New Zealand – and has been doing so for at least the past ten million years. The obvious question is ‘what next’ – something that has exercised seismologists and vulcanologists for generations. One way of finding out is to look back into the past, figuring out where fault lines are and how often they move.

Karaka Bay - on the eastern side of the city where Port Nicholson opens out to the sea through a narrow channel.
Karaka Bay – on the eastern side of the Miramar ‘was-an-island-before 1460’ Peninsula

That’s certainly been a focus of ongoing work in New Zealand, which straddles the collision between the Australian and Pacific plates and is prone to massive earthquakes. And of all the historical quakes, it seems few were as spectacular as the series that ripped through the country around 1460, as an indigenous Maori culture began to emerge from its Polynesian settler origins. All of them were around magnitude 8 or higher. They began, it seems, in the south as the Alpine Fault moved. Then there was a quake off what is now Wellington. And another in the Wairarapa. And another at Ahuriri, creating the Te Whanganui-a-Orotu lagoon. Wham! Tsunami followed, 10 metres or more high.

Maori refer to the 1460 Wellington quake as Haowhenua – the ‘land swallower’. Superficially that’s a paradox; the quake created land, raising the channel between Miramar, then an island. But the quake also triggered tsunami, washing far around the coasts and inundating settlements and gardens on the south coast of the Wairarapa. For Maori, the key issue was the loss of food-stuffs by a disaster that had, literally, swallowed their land.

It's all in an ordinary industrial-style street.
This movie studio in central Miramar was underwater before 1460.

A succession of quakes of this magnitude remains unprecedented. Seismology, to date, has usually treated quakes as independent events. And yet it’s clear that earthquakes occur in clusters, and seismologists have been asking questions of late that point to connections. One of those is interactions between fault lines. A quake on one fault might deliver enough energy to a nearby fault to trigger it, providing that fault was already under stress. There is also the effect of ‘slow quakes’. This only emerged in the early twenty-first century when GPS measurements revealed that, at certain points where the Pacific plate dives under the Australian – usually east or west of the New Zealand land mass itself – there are areas where the two slip slowly, but not smoothly. Huge earthquakes follow, but the energy released is spread out over months and not detectable by conventional instruments.

What these quakes seem to do is stress shallower fault lines, east in the plate interface. Current analysis indicates that a slow-slip quake under Kapiti island in early 2013 was likely cause of the succession of conventional quakes that struck in a semi-circular arc around Kapiti from mid-2013 – the Cook Strait and Grassmere quakes of July and August; the Eketahuna quake of January 2014; and the Waipukurau quake of April 2014.

All were severe quakes, but not in the league of the 1460 series. As yet the jury’s still out on the linkages. If the hypothesis is right though, the issue is obvious. Slow quakes might provoke successions of conventional shallow quakes in New Zealand. And if the 1460 sequence was one of those, it’s clear these quakes can be large indeed.

That begs a question: what would happen were New Zealand to suffer a similar quick-fire succession of huge quakes? That’s something I’ve tackled in my book Living on Shaky Ground (Penguin Random House). I won’t repeat the details here – suffice to say, it’s spectacular and I can’t help thinking that Mars looks appealing about this time of year.

Copyright © Matthew Wright 2014

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10 thoughts on “Forecasting New Zealand’s seismic apocalypse

  1. Very good blog to read. I am a California kid who remembers the earthquakes as a child. Unless you’ve been in one you can’t really know what they can do. I do plan on reposting this on my blog unless you have some objection. Thanks for sharing.

    1. Hi – glad you liked the post. Earthquakes strike chords on all sides of the Pacific, something we have to live with – a shared experience. Yes, if you’d like to re-blog, please do so – and I very much appreciate you asking first!

    1. Hi – many thanks for the offer. I’m definitely interested. I’ll have to talk to my publicist at Penguin Random House, though, they’re responsible for such matters as distribution of review copies!

  2. Reblogged this on Shirley McLain and commented:
    This is a blog my MJ Wright that does some explaining about earthquakes. He lives in New Zealand with lots of seismic activity. I remember as a child in California being shaken out of a chair while I was holding on as tight as I could. I’ve watched every seem in our house crack and the refrigerator and cabinets empty. I would rather be in a tornado than a earthquake because at least with a tornado you have some place to go for safety. With an earthquake you have none. Enjoy the read. Shirley

  3. I am sure you have mentioned this but will it be available on Kindle and if so, when? Looking forward to reading what you see as happening if there is a similar quake succession. Best of luck with this one and, of course, with all your books.
    Karen

    1. Thank you! My understanding is that it will be issued as an e-book, though possibly via Kobo which is where most of the Penguin Random House e-book editions seem to be issued. They usually let the print edition sell through for a few months first. I’ll certainly keep you posted.

    1. I’d go as a tourist for sure…want to wait on a better ion drive and a 30 day transfer orbit before venturing there, but that’s realistic near-term tech. Could be done with the popular and political support. Worked for Apollo!

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