14/04/2017, 12 noon.
What we learned this month
First and foremost, I’d like to acknowledge the huge amount of science understanding gained and shared. This is highlighted by the papers led by Ian Hamling, published in Science last month and Anna Kaiser, which is about to be published. These papers confirm what we know: the earthquake that rolled through Culverden, Waiau, Mt Lyford, Kaikoura, Ward and Seddon was more complex than we could appreciate early on in the response. That earthquake moved the South Island six metres closer to the North Island, with 21 faults moving in sequence in some sort bizarre choreograph movement, like a chorus line of dancers. Together they shaped and moved the South Island in ways we didn’t think were possible, but the impossible seems to apply to New Zealand regularly.
I reflect back on the paper I led after the M7.1 Darfield Earthquake back in 2010; I thought we were fast at publishing, and that we knew a lot, but our effort back then was a pale shadow compared to what Ian and Anna and their co-authors have produced and published in five months. The use of InSAR (information from the satellites) is changing the face of geophysics rapidly. Ian and his team are at the forefront of that movement, sifting with amazing speed through the avalanche of data, and Anna and her team were close behind with a raft of techniques.
Speaking of awe, I’d also like to acknowledge Laura Wallace’s contribution of finding the South Island’s first ever recorded slow-slip event that was triggered by the M7.8 Kaikoura Earthquake. It took us some time to determine exactly what happened, and some extra fieldwork to supplement data provided by our network. Land Information New Zealand (LINZ) has been providing us with funding for years to develop and sustain part of our GPS network, along with EQC. Because of this valuable network, we can keep on top of the slow-slip activity throughout New Zealand. Thanks LINZ and EQC! And, speaking of government support, another big thanks to the Ministry of Business, Innovation, and Employment, for helping us fund a large part of the science response to the Kaikoura earthquake.
We can confirm there were huge land movements and shaking near Waiau, among the strongest ever recorded – more than twice the force of gravity. Compare that to passengers taking off in a plane who experience about 10% of gravity, while roller-coaster riders get 1g. The people of Waiau held on through shaking of a strength and violence I don’t like to imagine.
And then there are the landslides. I feel like I need a whole other message just to address our landslide team. Our landslide team have mapped over 5,000 landslides so far due to the earthquakes. Ex Tropical Cyclone Debbie complicated matters greatly, triggering further slips and slides throughout the country. Our beautiful mountains, newly (geologically speaking) arising from the seafloor, haven’t had much time to erode, making them very vulnerable to landslides. So our landslide team is run off their feet at the moment with the combination of earthquakes plus terrible weather.
Naming the Kaikoura Earthquake
Thinking about the shaking in Waiau, there have been some issues raised about naming the earthquake the M7.8 Kaikoura earthquake. After all, the epicentre was closer to Waiau than Kaikoura. And Waiau experienced much stronger shaking, although we did not know that at the time. I will say that naming an earthquake is always a pretty difficult task. Some people would rather we never use their town or city’s name for an earthquake, while others feel that by not using their town’s name we are ignoring them.
When considering naming an earthquake, we take into account a number of factors. It was very difficult to name an earthquake like the one that occurred on the 14 November. With so many faults implicated across more than 150 kilometres of land, and a mountain of data, it was hard to know where to start. In this case, we chose to use a town near the mid-point of the action, near the Kererengu fault, one of the earliest surface faults identified. Also, Kaikoura’s shores were battered by a tsunami reaching up to seven metres above sea level, and their shoreline was raised permanently. But we did not intend to ignore other affected townships like Waiau, Culverden, Hanmer Springs, Ward or Seddon and I apologise if anyone feels they were ignored by us. My team and I think about those townships every day and we will continue to work on your behalf to understand this earthquake and its implications better.
A word about the GeoNet team
Small successes are everywhere; I’ve finally convinced ALL my team to take leave! Many worked over the summer holiday period, just too passionate and stuck into their work to take a break. It has not been an easy task to convince them to take a moment to step away from their computers. Indeed, it is the most challenging part of the job, to get the team to look after themselves.
Our GeoNet website will shortly be completely updated (22 May is tentatively our go live date); you can get a sneak peek here: beta.geonet.org.nz. We need your help to make it better, so please give your feedback.
Stepping away briefly from the science, I’d like to acknowledge the teams that keep us running behind the scenes and often don’t get much acknowledgement. During the Kaikoura earthquake, our website took a massive 250 million hits in 24 hours, peaking at 35,000 hits per second. And it held. We never lost connection to our website or our data streams, thanks to the hard work of our Platform and Development teams. We could not be GeoNet without them, so thanks to you!
Looking ahead for the six-month anniversary of Kaikoura, we’ll have some more exciting science stories planned!
Ken Gledhill (with special thanks to my co-writer, Sara McBride, for keeping me on topic and ensuring I make sense!).