PSN-L Email List Message

Subject: Re: Lehman seismograph
From: "David Saum" DSaum@............
Date: Sun, 31 Dec 2000 12:40:53 -0500

> The only feasable place for me to place the seismograph seems to be in my
> which has a thin carpet in it over a concrete floor. Do I need to cut the
> carpet away(the size of the Lehman base)? What do you think of the idea of
> using VERY LARGE and SHARP screws that would penetrate the carpet and they
> can also be used for Leveling? I have heard of some people using their
> seismographs on other than the ground floor (wouldn't the waves be
> baffled/diminished)?

I do not think the carpet should be a problem unless
it is thick enough to make leveling unstable.

My Lehman sits on a carpeted basement floor.  I do not seem to have
any sensitivity problem with this arrangement.  I originally had flat ended
leveling bolts contacting the carpet but I found that when they were
adjusted they snagged bits of carpet, and that made leveling difficult.
was fixed by putting round headed "cap nuts" on the ends of the bolts.
It is difficult for me to see why a carpet would attenuate the coupling
of the pendulum with the typical 10 to 20 second seismic signals.  It seems
more likely that higher frequency noise that is not of interest would be
attenuated by the carpet.  I do have several bricks on top of my Lehman
base for added stability.  Although the leveling drifted for the first week
after startup, it has not required adjustment in months.


Dave Saum


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Larry Cochrane <cochrane@..............>