As most of you have probably heard, there was a major EQ in Christchurch on Tuesday.
We are fine. All our friends in Christchurch are, as far as I know, physically well, though many houses are trashed (or “owned” as one persons 14 year old described it), we have yet to hear if any of our friends will be homeless.
Though this EQ was “only” a 6.3, the damage was much worse than the 7.1 on September 4th. One reasons was it was much closer to the city center- only 10km compared to 40 km, and it was very shallow.
The ‘modified mercalli’ shaking was higher. But that does not tell the whole story. (Though the whole story will take time as the Geologists and engineers study the aftermath.)
Earthquake intensity is a measure of the total energy released, which is intensity * time. This quake was short, but very intense, so while the total energy released was 1/10th of the September 4th quake, the shaking was much worse. They measured lateral accelerations of 1.88g in one location! That is *heaps*, the most ever recorded in NZ (though such instruments were not around in the long past), and maybe the most intense recorded ever? Not sure on that.
Image turning you house on its side and shaking it. Now image turning it on its side, hanging a second house off the it, and shaking it. That is the short of energy those structures had to absorb.
Either way, 1.88g exceeds the building code, even the strict code we have here. So it is not a surprise that some buildings went down, it is a surprise that more didn’t.
They have declared a national emergency for the first time in NZ history. Teams are coming in from around the world. I am on standby with WEMO (Wellington Emergency Management Office), waiting to see if I will be sent down to help. I’ve been doing civil defense for about 4 years, and have a bunch of formal qualifications, and it would be nice to help.
The reaction of the people, both in Christchurch and around the country, has been inspiring. Good folk. Sure, there are some ratbags out there taking advantage, but they are a minority. But on the whole people have taken responsibility and gotten stuff done, none of the helpless flailing and blame seeking that we saw after Katrina.
(And I am feeling rather merciless to people who exploit after events like this. I say we use the emergency powers and ship them all off to the Auckland Islands so they can learn how community spirit works, or die trying.)