Monday 1 June 2015

Earthquake Magnitude: Wow

So the other day a magnitude 8.5 earthquake hit off the coast of Tokyo.  By off the coast, I mean a bloody long way away.

Take a look at this map:

It shows what I would consider to be a 'normal,' earthquake, whatever normal means in the context of the earth trying to undress itself.  You can see the key on the bottom, the epicentre was miles and miles away from land, but the effect were still somewhat apparent.  I don't remember this one, which means it was probably too small for humans to notice.  (I'm incredibly sensitive to earthquakes.  For whatever reason I'm always the first person to notice them in a room.)




Now compare the above with the earthquake that happened the other day:

 
Something of a difference.  The epicentre was once again bloody miles away, but it shook the whole country an awful lot.  I was in one of the yellow zones, making it about a 5.2 where I was.  Let me tell you, a 5.2 is pretty big (these scales are logarithmic) and quite interesting on the fourth floor.  I can only imagine what one of those is like when you're a hundred storeys up.  Then again, any building that size will have a counterweight or massive shock absorbers, so I doubt they'd rock and roll as much as I might imagine.  A lot more than when a big lorry goes past your house though.
 
 
The thing this image doesn't convey is how long they last.  I've found that the bigger shakes last longer, and this one was upwards of a minute and a half.  It started relatively small but conitnued for a while, building to a crescendo before shaking a small amount for a while.  I've found that if a small shake lasts for a while, it usually means there's a lot more coming your way.  I've not come across any that start abruptly, they always seem to lead into it.
 
If you're wondering, the worst part is when the ground goes up and down.  There's no stomach turning feeling like that you might experience in a plane, it just kind of jostles a bit.  The reason that's the worst though, is because I can't imagine many materials being designed to withstand variable forces both laterally and vertically, it's not a typical building requirement.  If you get caught in the wrong place at the wrong time, the ground can move vertically by metres, hence the formation of waves that cause tsunamis.  I don't think this particular episode caused any tsunamis, but I'm not exactly Mr. Ear To The Ground in that regard.  Now that I think about it, I'm not that in any regard.
 
If you're wondering where I got this information from, it's this website:
 
 
 
 
You can get information about quakes in Japan, as they happen, from this site.  They keep records too, so if you hear about an earthquake in Japan you can check it out and see where was affected and how big it was.

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