Good Morning Geoffrey,

You might consider if quake signals can be less strong  than the noise 
but with a difference that makes them easily detectable.  That seems to 
be the situation.

If quakes create a higher frequency wave than the noise frequency, then 
it is possible for the quake signal to be detected  by high pass 
filtering.  Natural seismic noise has a peak of about 0.2 Hz but quakes 
have a very wide range of frequencies.  Local quakes have frequencies up 
to 10 Hz and higher, as do distant quakes.  Admittedly, the higher 
frequencies from distant quakes are more rapidly attenuated, but the 
higher frequencies are  usually still present in very distant quakes if 
we look for them.

I would suggest that you strive for peak noise counts of about 100 on 
the raw data.  On my 24 hour helicorder screen, that is too much noise 
so I HIGH PASS filter at 1 Hz.  That results in a screen that nearly 
always shows any quake activity, both local and distant.  Admittedly, 
some local man-made disturbance also is seen, but it is easily 
distinguished from  the distinctive quake signature.

Two examples can be found on the PSN website at 
http://www.seismicnet.com/cgi-dos/eventfiles.exe?Year=2010&Month=12&Day=&SID=ebgz

Please filter these recordings with a 1 Hz  high pass filter to see the 
quakes.

Roger
> Subject: Re: Amplifier gains
> From:    Geoffrey
> Date:    Sun, 19 Dec 2010 22:59:23 +0000
>
> It seems so simple to me,
> just hook up everything and increase the gain
> until the noise is seen and possibly
> to the most noise you can take
> as acceptable. To me that is possibly
> less that 6 counts peak on the average.
> You will notice a sensitivity in the
> hundreds of nanovolt range coming in
> from the sensor.
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