PSN-L Email List Message

Subject: Re: Geosource MD-100 geophones
From: John or Jan Lahr johnjan@........
Date: Wed, 25 Jun 2003 21:03:11 -0600

Hi Richard and Jim,

The AS1 system has a period of about 1 Hz and yet can often see
surface waves with a period of 10 s or a bit longer.  I think the
advantage of the AS1 system over a small refraction geophone is that
the magnet/coil arrangement has a larger volts out per velocity in.  In
any case, if I lived near any earthquakes I would give a 10 Hz geophone
a try.  If the event is close enough, it will have some energy at
frequencies above 1 Hz.  But then again, the signal from the geophone
may be less than the electronic noise of the amplifier for all but
the largest events. One could boost the signal from the small
geophones by putting 5 in series.


At 09:27 AM 6/25/2003, you wrote:
>Richard- Consider that all geophones roll off like a 2 pole filter-
>ie- 12db/oct or 40db/decade
>so   10Hz to 1 Hz you have 1/100 attenuatiom
>and 10 Hz to 0.1 Hz you have 1/10,000 attenuation
>It does not leave much to record.....Jim/UNLV
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