Monday was the provincial anniversary holiday in Wellington, New Zealand. Kind of cool – the provinces were abolished in 1876, but we still get the holiday.
Around 4 pm the house began shaking – slowly at first and then quite violently. We get a lot of small quakes. This wasn’t one of them. In fact, it seemed up there with last year’s big quakes.
The science behind it is fascinating. New Zealand has an automated seismic network that publishes estimated figures to the internet in near-real time. The first official figures – calculated by the duty seismologist – were available within fifteen minutes, with a final refined value just over an hour afterwards. This quake, at magnitude 6.2 and with an epicentre near Eketahuna in the Wairarapa, was classified ‘severe’. It was 33 km deep – felt widely, but not so destructive as the shallow quakes that hit Christchurch in 2010-11 and Wellington in 2013. It occurred in the Pacific plate subduction zone, where the plate is being driven down by the Indo-Australian plate riding up over it. It’s no coincidence that this is right under New Zealand – the islands are a product of that collision.
Where I live the ‘felt intensity’ was at the high end of V on the Modified Mercalli scale. Damage around Wellington included the Weta workshop model of a Hobbit eagle in the airport terminal, which crashed into the food-court. It was worse across the lower North Island in centres like Palmerston North. Fortunately nobody was killed or hurt.
Quakes have been on the rise in New Zealand lately. Archaeological work reveals that quakes cluster in decades-long patterns. The late twentieth century was one of the calmer periods. And now it looks as if we’re back in the action again. Christchurch, alas, may have simply been the beginning. Are they linked? Possibly. Certainly a quake in one area can increase stresses in a fault nearby that’s already under tension. But there also seems to be a general process of rising and falling activity.
Best case is it will settle down. Worst case – well, there is a disturbing precedent from the fifteenth century, where a succession of massive quakes estimated at magnitude 8+ tore along the length of the country over just a few decades. One of them, circa 1460, struck just south of Wellington and filled in one of the two harbour entrances, the Te Awa-a-tia channel. Motukairangi island – modern Miramar – became a peninsula and the water within its hills swampy terrain. Peter Jackson’s studio is built on the uplifted land.
Maori named the quake Haowhenua (‘the land destroyer’). The evidence is still visible as the flat land of Miramar and the Wellington airport flats – and as beach lines at Turakirae Head. The name seemed a puzzle – a ‘land destroyer’ that produced uplift? Then archaeologists discovered evidence of 10-metre tsunamis at the same time.
The question is not ‘if’ this will happen again – but ‘when’. New Zealand has many fault lines – the largest is the Alpine Fault, which moves about every 300 years and generates quakes of magnitude 8+. We are due for one, statistically, within 50 years. Recent studies point to the existence of other large faults each side of the South Island. They are still being researched. Scary? No. We have to accept the reality as it unfolds – and be prepared.
Do you live in an earthquake zone? If not, what natural disasters do you face?
Copyright © Matthew Wright 2014
Coming up: More writing tips, science geekery and humor. But hopefully not more quakes. For a while, anyway.