Barry,

If I didn't know better I could sure believe that you were seeing 
earth modes.  Another source could be from aliasing in the decimation 
process, but I don't think so.

You may want to check
http://books.google.com/books?id=aqjU_NHyre4C&pg=PA104&lpg=PA104&dq=masters+Widmer+Free+oscillations&source=bl&ots=nYbyuZBnAA&sig=9WR44L6fhaEYx3FL_1wwtyoulyw&hl=en&ei=Lnd7TZ2mJobg0gGImITQAw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBUQ6AEwAA#v=onepage&q=masters%20Widmer%20Free%20oscillations&f=false 
(Make sure this doesn't get split up in the e-mail.)

and

http://homepage.oma.be/mvc/osclibres/Free_Oscillations.ppt

I'd probably want to ignore the maths, but they have good 
explanations and lists of the many frequencies that have been 
predicted and observed which you could check against what you are seeing.

Regards,
Brett



At 12:15 AM 3/12/2011, you wrote:
>Hi Brett
>I made a file from 12:00 UTC to 24:00 UTC on the 3/11. I see a fft 
>peak at ~ 245 sec.
>see
>http://www.seismicvault.com/sitebuilder/images/110311_120000_ch1_psn_fft.gif
>Regards
>Barry


__________________________________________________________

Public Seismic Network Mailing List (PSNLIST)

To leave this list email PSNLIST-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.