PSN-L Email List Message

Subject: Re: FILTERS
From: Karl Cunningham karlc@.......
Date: Sun, 01 Oct 2000 19:52:25 -0700

Hi Jim --

Also living in So. Ca, I looked at a few of my event record for events in
the 50-100km distance range.  There is significant energy out to about 6Hz,
and to 10Hz for some events.  I believe that the closer the event,
relatively more energy will be seen at higher frequencies.  Given that, I'd
use not less than a 10Hz filter.  20Hz or more may be better.  Then, see if
you can still get distant events without them being swamped out by noise.

If they are, it may be necessary to have more than one channel, each with a
different filter.  They can all originate from the same output of your Lehman.

If you use Winquake, you can use the filtering capability to see what it
looks like before you build hardware. When building hardware, I'd suggest a
multi-pole filter (Bessel characteristic), if that's feasible.

Karl Cunnihgham
La Mesa, Ca.

At 15:02 10/1/2000 EDT, you wrote:
>I have a long period (20 sec.) Lehman sensor and live in So. Calif. where 
>there is usually a lot of seismic activity between 1.1 and 2.5 magnitude.  
>Could someone advise me of the appropriate frequency filter I should have to 
>monitor quakes at long distance (worldwide) and concurrently the ones that 
>happen locally.  Should it be a low pass filter set at 3hz, 10hz or 20hz?
>do I need a separate short period seis. for local quakes?
>Jim Allen
>Cerritos, Calif.


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