Evening star., 1963-03-01
: BY EARL III. VOSS
Star staff Writer

@AANS - gAOWA 4CAA
nessee mountain top by som
OF the worlds best practitioner
OF an ancient art-seismology
What these seismometers fin
or fail to find can have a direc
bearing on the nuclear test bal
talks, now in another crucia
stage in Geneva.
Instruments inside the cylin
ders are so sensitive they car
detect earth movements mucl
smaller than the diameter of {
FLU virus. They have to be al
least that good, hopefully much
better, to do the job American
diplomats d are expecting o.
them: Catch any violation of 9
nuclear test ban.
Nuclear explosions under.
ground at the Nevada test site
produced earth movements ir
Tennessee, 1000 miles away
that m easured only a few
thousandths of one millionth Of
a meter, much smaller than the
diameter Of the smallest virus
Interference Is Problem
But the slightest interference
can jam the system. Once q
spider Matched inside one OF
the sealed cylinders and began
spinning its web. Each free
flowing swing on the web pro-
duced a perplexing undulation
in the amplified seismogram.
Other noises" or earth
movements can confuse the
scientists. Interference from
passing trucks or trains, or
from oceans beating on distant
shores, can cause the line on a
seismogram to zig and gag so
much it completely masks a
small earthquake or explosion
far away.
To overcome these handi-
caps, the experts have found
that by placing a group Of
Seismometers in some regular
pattern over a two -square-mile
area. the movements from all
the instruments can be mixed
so the nearby noise can be
filtered out"
At the Cumberland Plateau
Seismological Observatory near
McMinnville, Tenn, the De-
fense Department is supervis-
ing installation of a 19-seis-
mometer array. laid out in
double hexagonal pattern about
2 miles across.
The most advanced station
Of its kind in the Western
world, it is the fourth of five
being constructed in the United
States. for long-range detection
Of earthquakes or nuclear ex-
plosions. particularly those in
the Soviet Union.
1t is patterned after the ar
rays foreseen by the Geneva
Conference of Experts from
East and West, held in 1858
Arrays were then expected tc
be placed inside the Soviet
Union. Now, however, the
United States has agreed Il
rely mostly on devices mainly
in this country. supplemented
with much less elaborate equip
ment inside Russia.
theoretically, distinguishing
between earthquakes and ex-
plosions should be possible by
studying the first earth move.
ments produced at a network
Of stations. Explosions initi-
ally push the earth out In all
directions and should produce
positive" or upward first
m otions" on seismograms
Earthquakes, most frequently
caused by slippage Of shelves
or huge walls underground,
should theoretically produce a
push-pull pattern Of signals
positive" first motions or COM
pressions in some directions,
downward or negative" first
motions, called rarefactions. in
others.
Thus any event causing ini-
tial downward or negative"
movements at a few of the sur
rounding stations should be
identifiable as an earthquake
It also should theoretically
be possible to locate under
ground events by noting the
directions from which it is re-
ceived at stations on various
points of the compass. using
simple triangulation method.
Blast Quake Detection
So far the most effective
method of distinguishing an
earthquake from an explosion
at long range is to determine
its depth of focus. Seismic
events deeper than 40 miles
can be ruled out from suspicion
as explosions-man has never
known to go that far down.
Closer to the surface, how
ever, both earthquakes and ex-
plosions produce reflections
that complicate the signal SO
much 1t is extremely difficult
to. calculate its depth precisely,
Above 40 miles depth other
methods Of distinguishing
earthquakes and explosions
must be found.
In using the first motion"
method of Identification
American scientists now believe
the impulse from distant dis
turbance must be magnified tc
be 10 times as powerful as any
intervening noise to give a
reliable conclusion as 10 Its d.
rection. With smaller signals
noise can obscure the first mo-
tion completely. or make ex.
polsions look like earthquakes
by changing some upward mo-
tions TO downward motions on
the seiSmograph.
Texas instruments Co. oi
Dallas. which built the Nc
Minnville station. is developing