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The Shaky Isles

I won’t make too much out of the recent effects of Seddon’s seismic activity on Wellington, at least until it gets any worse. Yesterday afternoon I was traversing through part of the Tinakori Hill, trying to determine how long it’d take to walk between the CBD and Ngaio. There’s still quite a lot of tree-fall and other storm damage up there, and elsewhere around the town belt, from that storm a few weeks ago [1], which made it interesting.

On this occasion I coincidentally ran into a friend from the Wellington Tramping & Mountaineering Club (Michael L). We were chatting for a few minutes, and the ground started to shift in a way that either of us could have perceived as general dizziness if we’d not confirmed with each other that it was an earthquake. Neither of us knew if there’s a protocol of what to do in an earthquake whilst in a forested area—maybe a worthy topic for another discussion—and then it stopped. Later, when I bumped into a woman walking her dog as she played on a smartphone, I was very surprised to discover that the shaking had been measured as magnitude 6.9 although it was later revised to 6.6. Somehow I’d felt nothing compared with what I’d have expected that to feel like.

I guess that’s related to it having been a shallow earthquake, and at the same time being not directly over its centre. To top it off for me, I was standing on some fairly hard rock (compared with the reclaimed land on which some of Wellington is built), and the solid rocky base would have dampened the effects. I don’t know…. My wife has an advanced geophysics degree and every so often I ask her things, but most of the time I just make stuff up and pretend to be an expert through virtue of being a local, despite having no real qualifications.

Compared with what an earthquake can do, neither this event nor the earlier event on 21st July, seems to have seriously affected Wellington yet, except for some minor damage and annoyances, and lots of local intrigue. Wellington’s in the news a lot due to being a population centre: People have been diving under desks, leaping into doorways (even though the doorway thing is no longer recommended by Civil Defence [2]), revising their earthquake plans, and yesterday there was the whole traffic issue. I found myself in Khandallah chatting with the train crew, who reckoned it’d be at least an hour before they knew if they’d be allowed to go anywhere, and after I resolved to wait for a bus, none turned up. So I walked all the way back into town again…. fortunately not such a bad night for a walk if one’s capable of walking. Apparently it was traffic chaos, and maybe all those people I passed walking in the other direction did not represent the numbers of a typical evening walking commute.

The township of Seddon however, further south and closer to the centre, seems to be more smashed up from yesterday’s activity [3], and clearly this is nothing compared with what many people of Christchurch and its surrounds are still going through following its series of earthquakes from late 2010.

We were still in Melbourne during the July 21st event. It’s frustrating when a place which you think of as home is going through something significant, and you’re stuck at a distance, unable to be there at the time. In an absurd way, and without wishing for any death, destruction, disruption, frustration, and heavy stress that has plagued other affected people in recent times as a consequence of seismic activity, I’m relieved that we’ve been able to get home for part of it.

It’s like a welcoming to The Shaky Isles [4].

2 Comments (Open | Close)

2 Comments To "The Shaky Isles"

#1 Comment By Ashley On 17 August, 2013 @ 10:33 pm

“To top it off for me, I was standing on some fairly hard rock (compared with the reclaimed land on which some of Wellington is built), and the solid rocky base would have dampened the effects.”

I’d be interested in your wife’s point of view Mike. I would have thought the “soft” or unstable reclaim to be more of a damper than solid rock (which should better transmit a shock wave).

– Ashley

#2 Comment By Mike McGavin On 18 August, 2013 @ 6:24 am

Hi Ashley. This is only the gist of it, but harder ground is much better at channelling vertical wave movements, whereas softer ground is more conducive to horizontal movements. Maybe think if softer ground a being like water, and then consider the waves? So it may depend a lot on the type of earthquake, but there’s usually more horizontal movement than vertical in most earthquakes. The reclaimed land around the harbour/CBD and other soft ground will probably have much more of a horizontal component to amplify in most quakes than rocky land has vertical, even though in a large enough or near enough earthquake you might not care.

As this is coming via me, though, there’s probably an element of mistruth or misleadingness to it.