New Zealand is living up to its namesake – the shaky isles – with a string of earthquakes over the past few days. The biggest was a magnitude 6.5 this afternoon in Cook Strait, the channel of water between the North and South Islands. The location of the earthquake was 17km deep and about 50km from Wellington, the capital of New Zealand. There are so far two reported injuries, no deaths and some minor damage in Wellington including cracks in roads and buildings, broken windows and even a collapsed ceiling at a medical centre. We didn’t feel anything here in Auckland.
As I used to do after a substantial earthquake in Christchurch, I jumped on Twitter and read the feed for #eqnz. I used to find it comforting to do this and to share my fear with other people going through the same thing. This time however, I got to read the twitter feed without any of the fear or terror that I used to feel. Someone posted a photograph of their local supermarket where bottles of water had completely sold out. For years now the New Zealand government has been urging people to stock three days’ worth of food and water in the event of just such an emergency. Yet a substantial number of people in Wellington of all places, have not done this. I’m sure Aucklanders are just as bad if not worse and we’ve got a volcanic eruption pegged for our future. It is very easy to do. You either buy bottled water next time you go to the supermarket or fill up empty juice or milk bottles with water and store them away somewhere. Could it be that taking precautions like this makes ignoring the reality of New Zealand’s geology that little bit harder?
Wellington is precariously positioned right on top of the plate boundary of the Pacific and Australian tectonic plates. Major fault lines capable of generating earthquakes of magnitude 8 or more run straight through populated areas of the city and important infrastructure. If a magnitude 6.5, 50km from the city can cause damage to buildings and generally freak everyone out, then I would be very worried about the future magnitude 8 right beneath it. Then there’s the Hikurangi Trench which is the subduction zone that runs offshore of Wellington that is capable of generating a magnitude 9 earthquake and a possible tsunami to go with it.
Wellington was lucky today to have that 50km cushion between itself and the epicentre. The distance from an earthquake epicentre is a crucial factor in the extent of damage a city can expect because energy from the rupture of a fault gets absorbed by rocks as it travels through the earth and so the intensity peters out with distance. A magnitude 8 right beneath a city will not have the chance to dump some of this energy before ramming into homes, buildings, bridges and more.
The other crucial factor, and many New Zealanders do not know this, is that bigger earthquakes last longer. While a magnitude 6 might only last for about 30 seconds or so, a magnitude 8 can last for several minutes. The 2004 Indian Ocean Boxing Day earthquake that caused a fatal tsunami had a duration of 8 to 10 minutes. What this means is that while a building may survive 30 seconds of severe ground shaking, it won’t necessarily survive 5 minutes of severe ground shaking.
Then come the aftershocks. A natural disaster is terrible on its own but with earthquakes, the disaster is repeated over and over again in the form of aftershocks and they come hard and fast in the first 24 hours, diminishing in frequency but not magnitude over time. But as people in Christchurch know only too well, they can continue for years. Sometimes, as happened in Christchurch, the aftershocks are more deadly than the initial earthquake. The first earthquake to hit Christchurch was on September 4th, 2010. It was a magnitude 7.1 some 30km away. There were no deaths. The fatal aftershock struck about 6 months later on February 22nd, 2011 killing 180 people.
Having been through all that an earthquake sequence has to offer, I’ve decided that I don’t care too much for it. I blacklisted Wellington as a potential holiday destination back on September 4th, 2010.
rachel.blog 
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