PSN-L Email List Message

Subject: Re: Caution on low pass filtering emphasis
From: Thomas Dick dickthomas01@.............
Date: Wed, 30 Dec 2009 16:29:21 -0600

RSparks 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: 
>    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.
are your sure the bottom is the raw data?? it looks a lot like my 
filtered data

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