PSN-L Email List Message

Subject: re: more seis feet
From: "David Saum" DSaum@............
Date: Mon, 1 Jan 2001 12:14:14 -0500

> If I don't see the microseisms I try to find out what went wrong.
> Seismologists have not gone to all the effort of piers, vaults, proximity
> to bedrock, etc, because they have too much money (fat chance), but to
> reduce the noise of the instrument environment.

Some of us are operating our systems under constraints
that rich seismologists never dreamed of.  For instance
my Lehman is on the carpeted slab in an office building
and my landlord would not be pleased if I damaged
the carpet.  I can imagine other non ideal locations
such as upper floors in buildings, but they may
be the only available or most convenient location.

Perhaps these "less than ideal" locations should
not be eliminated without an experimental test since there
seems to be no basic physics that excludes them a priori.
The two most important empirical tests seem to be:

1. is the level stable over time?
2. can it detect microseisms?

My one data point with a Lehman on carpeted floor suggests
that detecting microseisms is no problem, and long term
level stability is not a problem if you are willing to put up
with noise spikes from occasional floor tilts due to building
operation and occupancy.

BTW: I liked the idea of resting the entire Lehman on a
slab of glass.  That might make the carpet even less of
a factor.  I will give it a try.


Dave Saum


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