PSN-L Email List Message

Subject: Caution on low pass filtering emphasis
From: RSparks rsparks@..........
Date: Wed, 30 Dec 2009 12:45:09 -0800

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: 
    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,


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