Roger-

Thanks for this reminder. I try to not filter, as a general rule and 
only resort to it when I can't see the signal without filtering.

George

At 12:45 PM 12/30/2009, you wrote:
>Hello All,
>
>I sometimes think that we amateur seismologist over-emphasize the 
>need for low pass filtering, with the unexpected result that we 
>destroy the fidelity of the earthquake signal.  To illustrate what 
>we might be losing, I posted my recording of this mornings Baja 
>quake using both raw data and HIGH PASS filtered data in the 
>WinQuake volume format.  The high pass was done using WinQuake 
>filters set at 1 Hz, two pole.
>
>Here is a link to the posting: 
>http://www.seismicnet.com/cgi-dos/makegif.exe?/quakes/0912/091230.185135.ebgzx.psn 
>The trace on the bottom is the raw data.
>As you can see, the quake was about 1677 km from this station but 
>there was still lots of high frequency (> 1 Hz) in the data.   If 
>filtered low pass below 1 Hz, this information would be compromised, 
>and as you can see, there is a lot of information to be lost.
>
>Something to think about,
>
>Roger
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
>To leave this list email PSN-L-REQUEST@.............. with the body 
>of the message (first line only): unsubscribe
>See http://www.seismicnet.com/maillist.html for more information.


George Bush
Sea Ranch, CA, USA
38.73775N, 123.48882W 

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)