Monday, December 5, 2016

Moving And Shaking

We had an earthquake. You’ve maybe read about it in the news. It was on 14th November, a little after midnight. 

Once the excitement of an earthquake is over, however, there is a considerable aftermath that doesn’t get reported – not in the international press, at any rate. You might find a story about some cows stranded on a piece of land, but that’s about it. So here’s an update on what has happened for my international readers.

Firstly, an earthquake is not “an” earthquake. It is one large quake followed by a number of aftershocks. These vary in intensity and location. Since the first quake there have now been over 5,000 aftershocks. Yesterday we had a big one, 5.5M, which gave a definite bump. I reported it on Geonet, which collates reports of felt earthquakes, and is the source of all the reporting for earthquake data.

Secondly, this was a BIG quake. The fact that it struck on the middle of the night in a sparsely populated region is probably one of the main reasons why there were very few fatalities. The second reason is that New Zealand houses are generally of wooden construction, which makes them far less likely to fall down in a quake. In fact, the buildings destroyed were either of older, brick construction, or hit by falling chimneys (of brick construction) from neighbouring houses. However, this chart shows that the energy released by this earthquake is greater than the sum of all energy released by ALL other earthquakes in the last six years. That includes the two that hit Christchurch in 2011. It is the largest recorded in New Zealand since the 2009 Dusky Sound quake.

Wellington is the nearest city to the earthquake, and the effects were felt here, even though we’re 200 km from the epicentre. After an event like this, buildings are checked to see if they’re in imminent danger of collapsing. One building, on Molesworth Street, was cordoned off at this stage, and several others were also closed. An aftershock did further damage to the Molesworth St building, and at this point it was “red-stickered” – condemned for demolition. After making their initial checks, engineers did more detailed work on buildings that had suffered damage, and over the last three weeks more buildings have been red-stickered. Other buildings need substantial remedial work before they can be reopened, but do not need to be torn down.

61 Molesworth Street being demolished
There has been considerable comment in the press about damage to newer buildings, which appear to have fared worse than some older buildings. Two in particular, the BNZ building on the quay (which was closed for several months after the 2013 quake), and the Asteron Centre on Featherston Street. Both of these buildings are designed to be quake-resistant – what we’re learning from this is that the design is not quake-PROOF: the idea is that the building will take the damage whilst preserving the lives of those inside. Buildings can be replaced. The current map of buildings that are closed or due to be demolished now stands at 25, although only five of those are to be demolished.

On the South Island, closer to the epicentre, there has been considerable damage to roads and rail. The coastal SH1 route to Kaikoura has been blocked by landslides in several places, and there is still some debate about whether that route will be re-opened, or whether a new overland route will be made to get to Kaikoura. The town itself, whilst not too badly damaged, is highly dependent on tourism for its survival, so with no road in at the moment many are facing loss of their livelihoods.

In the nearby Marlborough wine region, there has been some damage to vineyards, and around 2% of wine stored at vineyards has been lost. This is not significant in overall terms, although obviously some vineyards have been badly affected. Storage for the coming harvest should be replaced in time.

Geonet have made some predictions about likely probabilities of aftershock intensity and frequency, and so far we have been at the low end of those forecasts. It’s fair to say we’re not out of the woods yet. There’s still a possibility of a large quake (6.0 or higher) over the coming weeks.

Closer to home, we’ve suffered some damage from both the original quake and the one yesterday. During the original quake, my toothbrush fell from its upright position, into the bathroom sink. And from yesterday, my shower sponge fell from its shelf onto the floor of the shower. Obviously we’ve lodged claims with EQC to cover these and we’re waiting to hear the outcome.

No comments:

Post a Comment