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New Earthquake 'Swarm' Hits North of San Francisco

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posted on Feb, 6 2010 @ 10:54 PM
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To Berkeleygal

With regard to KCT and other coastal stations, most of the
undulations are caused by the ocean surf. As already mentioned
wind can also cause noise but it is usually looks somewhat different.

The ocean surf causes the earth to sort of ring at very low frequencies.
Sometimes if there is a very high surf, those oscillations can travel
much further inland and can be noticed on stations further inland
form the ocean.

This is my first post and I hope it helps.

EngTech36



posted on Feb, 8 2010 @ 05:56 AM
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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



posted on Feb, 8 2010 @ 01:41 PM
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Hey! My thread is still going! The swarm is also still going. I have been out buying canned food and staples with an expiration date of 2012 on them ;-)
*Waves to Mike*



posted on Feb, 9 2010 @ 01:59 PM
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Does this figure into anything??? Not far from San Francisco....just curious




aslwww.cr.usgs.gov...



posted on Feb, 9 2010 @ 02:25 PM
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Oat Mountain helicorder just outside of L.A. less than 10 minutes ago, look's interesting....




quake.usgs.gov...




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