First storms, and now earthquakes! This is not altogether surprising, because there are a mass of fault lines nearby that are caused by the Pacific and Australian tectonic plates grinding by each other. These quakes were centred in Cook Strait, with the small town of Seddon, which is in the northern part of the South Island, being the closest habitation, but it was also not very far from Wellington. The first bigger one was just after 9 am on Friday and was 5.7 on the Richter scale. The news media made quite a fuss about it, with various comments about how scared people were, but I was in the rather odd position of hearing about it first from my wife about two hours later. I had seemingly been driving into Lower Hutt, but it was also interesting that I saw a number of people later, talked to some, and nobody mentioned the quake. Obviously, it was not serious.
There was an after-shock later in the afternoon, which created discussion, not the least because, since we could barely feel anything, I thought it was nothing more than some nearby road works, which I knew were going on because I had to avoid some seriously heavy machinery a little earlier in the day.
Then, two days later, while lying in bed and wondering whether to get up, there was another from the same place, this time at 5.8 on the Richter scale. Again, nothing to be particularly bothersome, but of course when you experience these sort of things, the real fear is not what is going on, but what it might develop into. My house is on a hill, and at the bottom of the hill, I suppose about 100 – 200 meters away, there is the main Wellington fault, and if it decides to go, it has seemingly generally produced shakes in the 8s on the Richter scale, and these are really serious.
Then, at 1709 hrs on the Sunday there was yet another. It started harmlessly enough, but it kept building up, and kept building up. After some time, I could hear the walls in the house straining, and just when I was thinking this could get really serious, it started to subside, but it kept going nevertheless, as was 6.5 on the Richter scale. Over all, it lasted a minute, which is not a very long time, but it feels like it in an earthquake. This time there were more serious outcomes. It was fortunate when it struck because there were relatively few people on the Wellington streets. What happened was that a number of windows on high-rises shattered, and sent sheets of glass downwards, and these might be the most dangerous in a quake. A quake of 6.5 disperses approximately 400 TJ of energy, or about 6 times the energy released by the nuclear bomb at Hiroshima.
Actually, Wellington is apparently experiencing a continuous “quake” this year. I gather that for several months, a massive land mass around Wellington is drifting north-eastwards, at something like a millimetre a week. Because this is smooth, at this rate the accelerating force is impossible to detect, and we would not be aware of it, but for physical measurements that depend on the GPS. We joke that airlines will probably raise their charges! On the other hand, the bulk of the South Island is not matching this drift, which means either a fault line is slipping, or strain is building somewhere, or both. These quakes could have involved the relief of this strain. The major fault lines that mark the tectonic boundaries are essentially north-south in direction with, if looked from above, a modest clockwise turn. From our point of view, we regard modest earthquakes as good. They do not do any damage, but they relieve strain, and strain is bad because if it builds up too far, the inevitable bang just gets bigger. We are just hoping there is no follow-up bang, through strain being transferred elsewhere.