posted on Feb, 8 2010 @ 05:56 AM
reply to post by EngTech36
Thank you very much for the input.
That's brilliant information and something I'd completely left out of the equation when I was considering
non-seismic causes. (I've spent far too much time peering at traces from Yellowstone, where the main problems are wind and cultural noise.
) But
yes, the surf would create traces like that; in fact as you say they do seem slightly different from wind. Could even be a combination of the two in
some cases.
For anyone who might be new to all this and who's looking at webicorder (online seismograph) traces for the first time, the lesson is that you should
not assume that what you see is always seismic. It's amazing how often it isn't. This is why if I see an odd-looking trace on one webicorder
I like to check others in the region to see what they show. Where there is a good net of webicorders in place it's always worth checking several, and
it's also very informative to find a map that shows their placement. Checking on weather conditions is also worthwhile.
The other thing that often freaks people out is when they see what looks like a big quake in the region they are looking at, when in fact it could
well be a larger quake has occurred even on the other side of the world and the webicorder they're viewing is picking up P (and S) waves from it.
(Quakes generate several types of waves but P waves often arrive first, followed by S waves.) For example, P waves from the Haiti quake showed up on
many webis all over the US.
So, before jumping to conclusions, it's vital to check a near-real-time data base like
this
one on USGS and see if there has been a big quake somewhere. If there has, note its exact time, then check its scientific data pages for
"Theoretical P wave travel times" to see when its P waves are expected to arrive at their webicorder's location. P waves move incredibly fast: the
ones from Haiti reached the Yellowstone webicorders in around 8 1/2 minutes.
Not all P waves from big quakes register everywhere in the world, though. There is a so-called "shadow zone" between around 104 - 140 degrees
longitude away from the quake and seismographs in that region might not pick up so much, if anything at all. The USGS website's glossary gives some
easy-to-understand info about the
shadow zone.
Mike