Tuesday, July 23, 2013

Not "The Big One"

Another Friday morning at work; so far, so normal. Then the building starts to shake. OK, we think, that’s happened before. But it doesn’t stop, and when the shaking suddenly gets worse, I followed emergency procedures and dived under my desk, and held onto the desk leg until the shaking stopped.

The information was on Geonet almost immediately: a 5.9 magnitude earthquake had struck just off the coast of South Island, near a “town” called Seddon (pop. 510).

Well, that gave us something to talk about for the rest of the day. There were some aftershocks, but nothing you could really feel, until mid-afternoon, when another shock of 4.6 magnitude rumbled through. Back under the desk again.

Throughout the weekend there were further aftershocks – you could feel the vibrations if you sat down or lay down perfectly still – but nothing really to worry about. That is, until late Sunday afternoon, when a really big one came through. Originally measured at 6.9, it was later confirmed as a 6.5 magnitude quake (by way of comparison, the two quakes which shook Christchurch in February and June  2011 were 6.3 and 6.4 magnitude).

There has been some damage to buildings in the centre of Wellington, including some broken windows, cracked concrete and roads, and damage caused by sprinkler systems going off, as well as the usual stuff falling off supermarket shelves and making a mess, which looks impressive in the news but isn’t really damage.

Damage in the BNZ building on Harbour Quays

On Monday morning, parts of the CBD were closed to the public, and Civil Defence were advising people not to come into work. Our Business Continuity Plan had already been brought into effect on Sunday night, with messages cascading down about what to do and whether to go to work. Monday was a “quake day” for us, so we decided to go and watch The World’s End at The Roxy, which seemed appropriate.

By Monday evening, most buildings had been given the all clear by structural engineers, and Nicola went into work as normal on Tuesday. The building I work in, unfortunately, is one of those that has not yet been opened – it’s apparently suffered some damage due to a ruptured water tank, so I’m still waiting to find out when I’m supposed to go back to work.

This series of earthquakes – a “swarm” in the jargon – is centred in the Cook Strait. It is not on the Wellington Fault, which is the biggest concern for Wellingtonians. (The whole city is built on a fault – way to go, early settlers!) Whether this series has increased or decreased the likelihood of a quake on the Wellington Fault is still a matter for the seismologists to figure out. However, the fact that the fault is known about is probably a contributing factor in the resilience of the buildings to the quake, as all modern buildings have been built to a more rigorous earthquake-proofing code, and older buildings have been strengthened.

We’re still getting aftershocks in the magnitude 4 range, which is just about at the limit of being felt. The likelihood of another large shock is decreasing, so they say, but it hasn’t gone away entirely.

No comments:

Post a Comment