reply to post by solarsicarian
Though they seemd quite big, those explosions would probably be too small to show up on either of those seismo stations. But okay, they might. If they
did, they'd be quite brief traces and without the classic P and S wave forms of quakes. With quakes, the P wave, being the fastest, arrives first and
then the S wave follows after it. (Measuring the time lag between the P and S waves is, in fact, a big part of determining how far away the quake is
from the seismo.)
The experts can differentiate explosions from quakes fairly easily. Eeven if there were multiple explosions close together then they'd similarly show
up as multiple, short traces, but still without the P and S forms that quakes have.
Powerful explosions (eg in quarrying or mining) can show up on some seismos and places like USGS keep an eye out for these and weed them out so they
don't get incorrectly posted as quakes. The auto-plotting equipment might register them as quakes if its parameters are set to simple measure
estimated ground acceleration, but the seismologists can review the traces and if there are no P and S wave form signatures then they know they aren't
quakes. In that case they delete them from the quake l;ists and move them to the "Mining Blast" or "Other Explosions" lists.
An explosion equivalent to around 1 ton of TNT would register as about a mag 2 quake on seismos that are sensitive enough to pick up smaller quakes.
To register a mag 3 would take an explosion of about 30 tons of TNT. A smaller nuclear test normally register somewhere in the mag 4 range.
Bit quakes are incredibly powerful...
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TrueAmerican, you were right, mate. You said there could be trouble with that triple junction and there has been. Now we can only hope
that things will settle down but frankly I don't like the look of this. I also was amazed when the JMA official said there was no connection between
the megathrust event and the Shizuoka quake. It was the largest quake in that region (of Shizuoka) in some years, but having told us that, he insisted
that there's no connection to Friday's quake.
Yeah sure. And I just saw another flock of pigs fly over.
You were right, mate.
Okay after midnight here. I'm outa here. Thanks for your efforts, TA. Sorry to tack this into another post but I'm knackered.
Mike
edit on 15/3/11 by JustMike because: I had a reason.