PSN-L Email List Message

Subject: instrument siting
From: sean@...........
Date: Mon, 1 Jan 2001 16:06:47 -0600 (CST)

You are way out of line and very mis-informed in stating that
seismologists are "rich". Over three decades I have seen amazing
self sacrifice and personal investment on the part of seismologists
to achieve the data quality that is required. The current new generation
of broadband instruments are so expensive that often the qualified
technical personnel to install and operate them have to be left out
of the budget, and volunteers have to try to do the work. The only
people who had adequate funding was the AFOSR (Air Force Office of
Scientific Research) during the cold war for installing seismic 
systems for nuclear test detection. Even the current CBTB (comprehensive 
test ban treaty) verification instrumentation funding is very limited. 
But for the most part, most seismologists have to do most of the work 
of preparing sites and installing instruments themselves because they 
cannot afford commercial contractors. And after a site is established,
the continuing operation is up to the scientists' dedication, like paying
the postage to mail data tapes.

We "rich seismologists" of course have never "dreamed of" such 
poor sites as a carpeted floor, because in the past 50 years someone
has tried it and found the idea to be a dud compared with what their
colleagues were getting from more carefully prepared (and probably
more difficult) sites. Even in the 20's era of mechanical-optical-
photo-recording instruments of quite low sensitivity, the quietness
and isolation of a pier in a vault was desired. Our old SLM vault at
St. Louis U. was installed deep under the lobby of a new gym in 1923
when a Jesuit (Fr. Macelwane) found bedrock there and twisted other
Jesuit arms to get it installed for free.

As for the site of a long period instrument, particularly a horizontal,
I would encourage everyone to make every effort to optimize the
site conditions. I don't think "easy" or "convenient" are valid
criteria if you want to record more than a few large quakes per 
year, like todays Ms 7.2 in the Philippines, which should have been
very well recorded by all the PSN instruments. The monthly-or-so M 6.0
events will be about 6% of this amplitude, and should also be clearly
recorded just to keep up interest (= maintenance/adjustment).

I routinely run preliminary tests of instruments in my lab on the third
floor of a very sturdy building (it was designed for 8 floors that never
got built because the Univ ran out of $$). Even adjacent to a 30"
square pillar, my lab floor runs at about a continuous Ms 3.0 quake.
The whole building tilts several micro-radians daily as the sun
warms the south side. Even the test pier in the basement is swamped
with the noise of the AC fans, the elevators, the streets, etc.
My only "good" test site is 40 km away in a WWII munitions bunker,
(black powder on the floor) but I still see the noise of the interstate 
about 0.5 km away.


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