On 4/27/12 5:39 PM, Hal Murray wrote:
Back to somewhat time-nutty stuff...
Does anybody understand how they are using GPS and/or have performance numbers?
They don't need the actual position (DC), just the changes in position. They
need it now. They can't wait for post processing. I'm not sure how much
accuracy they need. I'd guess in the cm range.
(Maybe I can learn more at the open house.)
I'm going to guess that GPS doesn't have much to do with the detection,
per se, an accelerometer works quite nicely. What you want GPS for is
precision timing, so you can figure out where the shock wave started and
is going, but combining data from multiple stations.
zipping along at a few thousand meters per second, timing to
milliseconds is probably good enough, but pretty darn tough to do in a
field site without something easy like GPS to give you a nice time hack.
the physical displacement during an earthquake isn't all that much (a
few mm or cm, unless you're right on the fault and/or it's a big one)
here's a M4 a couple months ago
http://earthquake.usgs.gov/earthquakes/eventpage/ci15141521#summary
shows max accels of around 0.2 %g (I assume that means about 0.002g, or
0.02 m/s^2)
that works out to a displacement on the order of mm, over a time of tens
of milliseconds.
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