LETTER TO WILLIAM J. CASEY FROM CHARLES H. PERCY

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP84B01072R000300050002-0
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 11
• Document Creation Date: December 20, 2016
• Document Release Date: February 28, 2007
• Sequence Number: 2
• Publication Date: October 15, 1982
• Content Type: LETTER

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EXECUTIVE SECRETARIAT
Routing Slip
ACTION
INFO
DATE
INITIAL
1
DCI
2
DDCI
3
EXDIR
4
D/ICS
I
x
6
DDA
7
DDO
8
DDS&T
9
Chm/NIC
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GC
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IG
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Compt
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D/EEO
114
1 D/Pers
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D/OEA
x
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C/PAD/OEA
17
SA/IA
18
A0/DCI
19
C/IPD/OIS
20
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22
Please prepare response for DCI's
signature - forward through D/OEXA.
Executive Secretary
18 October 1982
Date
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 Approved For Release 2007/02/28: CIA-RDP84BO1072R000300050002-0
CHARLES H. PERCY. ILL. CHAIRMAN
HOWARD H. BAKER. JR.. TENN. CLAIBORNE PELL. R.I.
JESSE HELMS, N.C. JOSEPH R. BIDEN. JR., DEL,
S. 1. HAYAKAWA. CALIF. JOHN GLENN. OHIO
RICHARD G. LUGAR. IND. PAUL S. SARBANES, MD.
CHARLES MC C. MATHIAS, JR.. MD. EDWARD ZORINSKY, NEBR.
NANCY L. KASSEBAUM, KANS. PAUL E. TSONGAS, MASS.
RUDY BOSCHWITZ, MINN. ALAN CRANSTON, CALIF.
LARRY PRESSLER. S. DAK. CHRISTOPHER J. DODD, CONN.
EDWARD G. SANDERS, STAFF DIRECTOR
GERYLD B. CHRISTIANSON. MINORITY STAFF DIRECTOR
October 15, 1982
Mr. William J. Casey
Director, Central Intelligence
Washington, D.C. 20505
Dear Mr. Casey:
In the attached article published in this month's issue of
Scientific American, Lynn R. Sykes and Jack F. Evernden state
that their analysis of Soviet weapons tests seismic data leads
them to conclude that the Soviets have abided by the 150 kiloton
threshold provided for under the Threshold Test Ban Treaty.
These writers also claim that using a relatively small seismic
network within the Soviet Union, the United States could verify
a comprehensive test ban with an extremely high degree of con-
fidence.
I should appreciate having the Central Intelligence Agency's
assessment of this article's conclusions, especially the above
mentioned claims.
Sincerely,
~~
Charles H. Percy
Chairman
CHP:gld
'Unrfei ,.fafez ..ienafe
COMMITTEE ON FOREIGN RELATIONS
WASHINGTON, D.C. 20510
 Established 1845
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SCIENTIFIC
AMERICAN
'The Verification of a Comprehensive
Nuclear 'Test fan
Networks of seismic instruments could monitor a total test ban
with high reliability. Even small clandestine explosions could be
identified even if extreme measures were taken to evade detection
by Lynn R. Sykes and Jack F. Evernden
Two treaties put into effect over the
past 20 years have set limits on the
testing of nuclear weapons. The
Limited Test Ban Treaty of 1963, which
has been signed by more than 120 na-
tions, prohibits nuclear explosions in
the atmosphere, the oceans and space,
allowing them only underground. The
Threshold Test Ban Treaty of 1976, a
bilateral agreement between the U.S.
and the U.S.S.R., prohibits underground
tests of nuclear weapons with a yield
greater than 150 kilotons. In the present
climate of widespread pressure for more
effective control of nuclear arms the
idea of a comprehensive ban on all nu-
clear testing is receiving renewed atten-
tion. Such an agreement would be an
important measure. It might inhibit the
development of new weapons by the
major nuclear powers, and it might also
help to prevent the spread of nuclear-
weapons technology to other countries.
A halt to all testing was the original
goal of the negotiations that led to the
1963 Limited Test Ban. New talks with
the aim of achieving a total ban were
begun in 1977 by the U.S., the U.S.S.R.
and Britain, but the talks were suspend-
ed in 1980. In both cases the main im-
pediment to a comprehensive treaty was
the contention by the U.S. and Britain
that compliance with the treaty could
not be verified because sufficiently small
underground nuclear explosions could
not be reliably detected and identified.
In July the Reagan Administration an-
nounced that the test-ban negotiations
with the U.S.S.R. and Britain will not be
resumed. Once again the primary reason
gi cn was a lack of confidence in meth-
ods of verifying compliance.
In 1963 the reliability of measures for
the verification of a treaty banning ex-
plosions larger than about one kiloton
may have been arguable, but it no long-
er is. We address this question as seis-
mologists who have been concerned for
many years with the detection of under-
ground explosions by seismic methods
and with means of distinguishing under-
ground explosions from earthquakes.
We are certain that the state of knowl-
edge of seismology and the techniques
for monitoring seismic waves are suffi-
cient to ensure that a feasible seismic
network could soon detect a clandes-
tine underground testing program in-
volving explosions as small as one kilo-
ton. In short, the .technical capabilities
needed to police a comprehensive test
ban down to explosions of very small
size unquestionably exist; the issues to
be resolved are political.
An underground explosion sets up
L3 elastic vibrations that propagate as
seismic waves through the earth and
along its surface. The waves travel great
distances, and seismic monitoring in-
struments in common use are sensitive
enough to record even those generat-
ed by very small explosions. Once the
waves have been detected the main task
is to distinguish the seismic signals of
explosions from those of earthquakes.
This can be done with a network of sev-
eral widely separated seismometers.
Two types of elastic vibrations can
propagate through the solid body of the
earth, that is, through the crust and the
mantle. The first waves to arrive at a
seismometer are compressional waves,
which are similar to sound waves in
air or water; the seismological name
for them is P.(for primary) waves. The
slower body vibrations are shear waves,
which are similar to the waves on a vi-
brating string; they are called S (for
shear or secondary) waves. An under
ground explosion is a source of nearly
pure P waves because it applies a uni-
form pressure to the walls of the cavity
it creates. An earthquake, on the other
hand, is generated when two blocks of
the earth's crust rapidly slide past each
other along the plane of a fault. Because
of this shearing motion an earthquake
radiates predominantly S waves.
A result of the spherical symmetry of
the explosion source is that all the seis-
mic waves it generates have a nearly ra-
dial symmetry around the focus of the
explosion. In contrast, the highly direc-
tional character of an earthquake source
gives rise to seismic waves with strong-
ly asymmetric patterns. The asymmetry
in the amplitude of the waves received
at seismometers throughout the world
provides the means whereby seismolo-
gists can determine the faulting mech-
anism of a given earthquake.
In addition to the P and S body waves
there are also two types of seismic waves
that propagate only over the surface
of the earth. They are called Rayleigh
waves and Love waves, and they result
from complex reflections of part of the
body-wave energy in the upper layers of
the earth's crust. A simple explosion can
generate Rayleigh waves but not Love
waves, whereas an earthquake generates
waves of both types.
Seismologists characterize the size of
a seismic event bye means of magnitudes.
A given event can be assigned several
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magnitudes, each one based on a differ-
ent kind of seismic wave. A magnitude is
the logarithm of the amplitude of a par-
ticular type of wave normalized for dis-
tance and depth of focus. Of the numer-
ous magnitudes that can be defined for
a single seismic event we shall discuss
only two, which in seismological no-
tation are designated M5 and mb. The
former is generally based on Rayleigh
waves with a period of 20 seconds, the
ffl
FEE
latter on one-second P waves. The mag-
nitude of a seismic signal is ultimately
related to the energy released at the site
of the event. For a nuclear explosion the
customary measure of energy release is
the yield in kilotons, where one kilo-
ton is the energy released by detonating
1,000 tons of TNT.
Every year there are numerous earth-
quakes whose magnitudes are in the
range corresponding to the yields of un-
derground explosions. Several methods
can be applied to several types of waves
to distinguish the seismic waves of ex-
plosions from those of earthquakes. The
locatiori of a seismic event and its depth
below the surface are important criteria;
indeed, the great majority of routine-
ly detected events can be classified as
earthquakes simply because they are ei-
ther too deep or not at a plausible site
for an explosion. The remaining events
can be reliably classified by the amount
of energy radiated in the several kinds
of waves at various frequencies.
The location of an event in latitude
and longitude is a powerful tool for clas-
sification. The position is determined by
recording the arrival time of short-peri-
od P waves at several seismographic sta-
tions in various parts of the world. The
travel time of the P waves to each sta-
tion is a function of distance and depth
of focus. From the arrival times it is
possible to determine the location of the
source with an absolute error of less
than 10 to 25 kilometers if the seismic
data are of high quality.
The identification of seismic events ai
sea is quite simple. It is assumed that thc
network monitoring a test-ban treat
would include a small number of sim-
ple hydroacoustic stations around the
shores of the oceans and on a few crit-
ical islands to measure pressure waves
in seawater. The hydroacoustic signal of
an underwater explosion is so different
NUCLEAR TESTS CONTINUE to be car-
ried out at a rate of about 50 per year, prin-
cipally by the two leading nuclear-weapons
powers: the U.S. and the U.S.S.R. As this bar
chart shows, the main effect of the Limited
Test Ban Treaty of 1963 (broken vertical lino )
was not to reduce the number of test expl4 -
sions but merely to drive most of them under -
ground. Nuclear test explosions in the atmo? -
phere and underwater are represented by co -
ored bars, those underground by gray bar..
 Approved For Release 2007/02/28: CIA-RDP84BO1072R000300050002-0
from that of an earthquake and can be
detected at such long range that the
identification of a seismic event at sea as
an explosion or an earthquake is simple
and positive. Hence any event whose
calculated position is at least 25 kilome-
ters at sea (a margin allowing for errors)
can be classified as an earthquake on
the basis of its location and the charac-
ter of its hydroacoustic signal.
The accuracy with which the position
of a seismic event can be determined in
an area offshore of an island arc has
been tested with an array of ocean-bot-
tom seismometers off the Kamchatka
Peninsula and the Kurile Islands in the
U.S.S.R. The tests indicate that the ac-
curacy of a seismic network under these
circumstances is much better than 25
kilometers. Holding to that standard,
however, one finds that well over half
of the world's seismic events are defi-
nitely at sea and are therefore easily
identified as earthquakes.
Another large group of detected
events have their epicenters on land but
in regions where no nuclear explosions
are to be expected; these events too can
be safely classified as earthquakes. In-
deed, almost all the world's seismic ac-
tivity is in regions that are of no concern
for monitoring compliance with a com-
prehensive test ban. Thus the simple
act of locating seismic events classifies
most of them as earthquakes.
C alculating the depth of focus pro-
vides a means of identifying a large
fraction of the remaining earthquakes.
From 55 to 60 percent of the world's
earthquakes are at depths of more than
30 kilometers; at least 90 percent are
more than 10 kilometers deep. Any seis-
mic event as deep as 15 kilometers is
certainly an earthquake. No one has yet
drilled into the earth's crust as far down
as 10 kilometers, and the deepest nucle-
ar explosions have been at a depth of
about two kilometers.
Several seismological procedures can
be employed to determine an event's
depth of focus. In most cases the depth is
calculated at the same time as the loca-
tion. When a seismic event is detected at
20 stations or more, a routinely calculat-
ed depth of 30 kilometers or more en-
sures with a 95 percent degree of confi-
dence that the event was at least 15 kilo-
meters below the surface.
A powerful technique for estimating
depth can be applied if at least one seis-
mological station is within a few hun-
dred kilometers of the detected event.
(A monitoring network for a compre-
hensive test ban would be quite likely to
meet this condition in areas where nu-
clear testing might be expected.) A pair
of P and S waves generated at the same
instant and recorded by a station near
the event follow identical paths but
propagate at different speeds. The dif-
ference in their times of arrival, or in
f 1A,
T' ~I ~'~t44T` .
FOUR TYPES OF SEISMIC WAVE are illustrated. The two waves at the top propagate
through the solid body of the earth; the two at the bottom propagate only near the surface. The
compressional body waves called P (for primary) waves travel fastest and are the first ones to
arrive at a seismometer; they are the predominant type of body wave produced by an under-
ground explosion. The slower body waves called S (for shear or secondary) waves vibrate in a
plane transverse to their direction of propagation; they are the predominant type of body wave
produced by an earthquake. The surface waves called Rayleigh waves and Love waves result
from complex reflections of the P and S body waves in the upper layers of the earth's crust.
other words the difference in their phas-
es, therefore serves to determine the
time of origin of the event. With experi-
ence the seismograms of a station near
the event can be successfully analyzed
to detect at least one pair of such P and S
phases. Given the time of origin deter-
mined in this way and the arrival times
of the P waves at only a few distant
receivers, an accurate estimate of the
depth of focus can be made.
There may remain critical seismic re-
gions where nearby stations do not exist.
.Data from large events can then be em-
ployed to refine the calculated depth
and location of smaller events. The es-
sence of the technique is to correct the
observed times of small events by noting
the differences between the observed
and the calculated times for a large
event in the same area. The procedure is
in routine use by several networks.
The combined effectiveness of loca-
tion and depth in distinguishing earth-
quakes from explosions is impressive.
More than 90 percent of all earthquakes
either are under oceans or are at least 30
kilometers deep (or both). Most of the
remaining earthquakes are of little inter-
est because they are in countries that are
unlikely to be testing nuclear weapons
or in countries where clandestine testing
would be impossible. For the U.S., of
course, the U.S.S.R. is the country of
prime interest. About 75 percent of the
earthquakes in and near the U.S.S.R. are
in the eastern part of the country near
the Kamchatka Peninsula and the Ku-
rile Islands. Almost all of the shocks in
these areas either have a focal depth
greater than 50 kilometers or are well
offshore. It turns out that seismic events
whose calculated position is on land in
the U.S.S.R. or less than 25 kilometers at
sea and whose calculated depth is less
than 50 kilometers constitute only about
.5 percent of the world's earthquakes.
This amounts to about 100 earthquakes
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PATHS OF SEISMIC WAVES are traced on a cross section of the earth. Body waves from an
earthquake or an explosion travel through the crust and mantle along the curved paths labeled
P, S, pP and pS. A pP wave is a compressional wave that is produced by the reflection of a P
wave from the surface of the earth just above an earthquake or an explosion; a pS wave is a
shear wave that results from the conversion of part of the compressional energy of an upward
P wave into transverse energy as the P wave is reflected from the surface. Surface waves such
as Rayleigh waves and Love waves diminish rapidly in amplitude with increasing depth. The
hypocenter is the focal point of an earthquake or an underground explosion from which the
waves radiate. The epicenter is the point on the earth's surface directly over the hypocenter.
per year with an Mb magnitude greater
than 3.8 for which other seismic dis-
criminants must be employed.
None of. the measures we have dis-
cussed so far relies on the detailed char-
acteristics of the waves radiated by
earthquakes and explosions. Several
powerful discriminants are based on
those characteristics, in particular on
the relative amounts of energy in waves
of different types and periods. For ex-
ample, a shallow earthquake generates
20-second Rayleigh waves with ampli-
tudes at least several times greater than
those of an explosion that releases the
same amount of energy. In the notation-
al practice of seismology the compari-
son of the two magnitudes is referred to
as the MS: Mb ratio, that is, the ratio
of long-period to short-period waves.
A second spectral discriminant is
based on the observation that long-
period P and S waves are rarely or nev-
er seen in association with explosions
but one type or the other is routinely
detected today by simple seismometers
for most earthquakes that have a one-
second P-wave magnitude of at least
4.5. More sophisticated seismic stations
and more sophisticated analysis of the
signals could lower the magnitude at
which such waves can be detected.
A third distinction is that surface
waves of the Love type are generated far
more strongly by shallow earthquakes
than they are by underground explo-
sions, including even abnormal explo-
sions. Still another characteristic feature
of the seismic signal from explosions is
that the first motion of the earth stimu-
lated by P waves is always upward be-
cause the explosion itself is directed
outward; the first P-wave motion in
an earthquake can be either upward or
downward.
An important factor contributing to
the separation of earthquakes from ex-
plosions on an MS: Mb diagram is that P.
waves from the two kinds of events have
different radiation patterns. Explosions
radiate short-period P waves equally in
all directions, whereas earthquakes have
very asymmetric patterns. Hence most
earthquake sources show a decrease of
from .4 to one magnitude unit from the
peak values when the P-wave ampli-
tudes are averaged over pertinent radia-
tion angles. A simple explosion does not
initially radiate any shear waves; earth-
quakes typically generate large shear
waves. As a result Rayleigh waves gen-
erated by many types of earthquakes
have a larger amplitude than the corre-
sponding waves generated by under=
ground explosions of the same Mb-
There is a characteristic time for the
formation of the source of a seismic
event; the time is equal to the maxi-
mum source dimension divided
by the velocity of source formation. The
source dimension for earthquakes is
the length of the break where most of
the short-period energy is released; it is
from three to 20 times greater, depend-
ing on the state of stress in the rocks,
than the radius of the cavity and shatter
zone of a comparable explosion. The
velocity of source formation for earth-
quakes is from somewhat less to much
less than the velocity of shear waves in
the rocks surrounding the fault, where-
as the relevant velocity for explosions
is the velocity of shock waves in the
rock, which is essentially the velocity
of compressional waves. As a result
of these differences in the size of the
source and the velocity of source forma-
tion the characteristic times for earth-
quakes and explosions differ by a factor
of from six to 40. It is therefore not sur-
prising that differences are observed be-
tween the short-period P-wave spectra
of earthquakes and explosions.
Observations of several U.S. explo-
sions have demonstrated the existence
of a phenomenon called overshoot. It is
related to shock waves in strong rock,
but it can be thought of as the equivalent
of cavity pressure rising to high values
followed by a decrease in pressure by a
factor of four or five; the lower pres-
sure is then maintained for many tens
of seconds. Overshoot, when it occurs,
provides additional P-wave spectral dis-
crimination and augments discrimina-
tion by means of the MS : Mb ratio for
larger events.
~t was once thought that an explosion
could not give rise to any Love waves
at all. A phenomenon that was of great
significance in thwarting President Ken-
nedy's effort to achieve a comprehen-
sive test-ban treaty in 1963 was the ob-
servation that many underground nucle-
ar explosions at the U.S. testing site in
Nevada, particularly those in hard rock,
generated unmistakable Love waves.
The failure of the qualitative criterion
"No Love waves from explosions" (at
a time when such quantitative criteria
as the comparison of the magnitudes
of long-period and short-period waves
were not adequately established) left
seismologists unable to guarantee their
ability to distinguish the seismic waves
of underground explosions from those
of earthquakes.
The presence of Love waves in the
Nevada tests has since been explained.
What was not considered in the earlier
analyses was the influence of the natural
stressed state of the earth on the waves
generated by an explosion. The creation
of a cavity and its surrounding shatter
cone by an underground explosion leads
to the release of some of the natural
stress, which in turn generates seismic
waves equivalent to those of a small
earthquake, including Love waves. The
observed waves are a superposition of
the waves from the explosion and from
the release of the stress.
The release of natural stress also al-
ters the amplitude of Rayleigh waves.
The perturbation has never been large
enough, however, to put in doubt the
nature of an event identified by the ratio
of long-period to short-period waves.
Only rarely does the perturbation signif-
icantly affect the amplitude of P waves;
it is not known ever to have changed the
direction of their first motion. More-
over, if the magnitude b'IS is determined
from Love waves rather than Rayleigh
waves, the ratio method (MS : Mb) pro-
vides an excellent discriminant.
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Ins short, if seismologists had done
their homework thoroughly by 1963,
the nations of the world might well have
achieved a comprehensive test-ban trea-
ty then. Today the release of natural
stresses in the earth is significant only as
a perturbing factor that must be taken
into account when the yield of an explo-
sion is estimated from Rayleigh waves.
Reports that earthquakes occasional-
ly have MS: Mb values like those of ex-
plosions have been cited as a factor that
might impede the effective monitoring
of a comprehensive test ban. In analyz-
ing a large set of earthquakes in all parts
of the world and of underground explo-
sions in the U.S. and the U.S.S.R. we
found only one example of this kind of
ambiguity. The focus of the event was
far from the area in which the seismom-
eter network gave its best results.
In 1972, at a meeting of the UN Com-
mittee on Disarmament, the U.S. sub-
mitted a list of 25 "anomalous" events
that were said to -be indicative of a prob-
lem in discrimination. In 1976 the 25
events were reanalyzed by one of us
(Sykes) and two other seismologists,
Robert Tathum and Donald Forsythe. It
was established that about half of the
events had MS: Mb values that put them
clearly in the earthquake population.
Most of the original magnitudes had
been determined from only one or two
stations, and much existing informa-
tion had not even been consulted. When
the records of other available stations
were examined, the events ceased to
be "anomalous."
For the remaining problem events
MS: Mb measurements based on 20-sec-
ond Rayleigh waves gave values in the
range characteristic of explosions. Sev-
eral of these events were at depths of
from 25 to 50 kilometers, where the pos-
sibility of nuclear testing can be exclud-
ed in any case, but the magnitude ratio
nonetheless demanded explanation. It is
known from seismological theory that
certain types of earthquakes at these
depths excite long-period Rayleigh
waves poorly. The theory predicts, how-
ever, that Love waves and vibrations
called higher-mode Rayleigh waves are
in many instances vigorously generated
in these circumstances. An analysis of
recordings of the Love waves and the
higher-mode Rayleigh waves identified
several more of the problem events as
earthquakes.
Only a single sequence of events at
one place in Tibet remained as a prob-
lem. In that region underground nuclear
testing is unlikely, but the nature of the
events could not be determined with cer-
tainty from the magnitude ratios. We
think the reason is that with the seismo-
graphic networks of the 1960's, when
the events were recorded, Love waves
could not be detected for small-magni-
tude events because they were obscured
by background earth noise. New instal-
lations and new modes of data process-
ing have greatly reduced the problem. If
the same series of events or a similar
series were to take place today, we think
they would be identified unambiguous-
ly. Long-period seismographs in bore-
holes and routine digital' processing of
seismograms lead to a suppression of
background noise and increase the de-
tectability of many types of waves, in-
cluding Love waves.
As it happened, the nature of the Ti-
betan problem sequence was resolved in
spite of the inadequacies of the long-pe-
riod data of the time. At several stations
the first motion of the P waves was
downward, which is not possible for an
explosion. Hence the events must have
been small earthquakes.
It seems reasonable to say that for the
networks we shall describe below there
should no longer be any problem events
at Mb 4 or more. We know of no Eur-
asian earthquake with a. one-second P-
wave magnitude of 4 or more in the past
20 years whose waves are classified. as
those of an explosion. Of course, nu-
merous smaller Eurasian earthquakes
during that period went unidentified be-
cause of inadequate data.) Furthermore,
to our knowledge not one out of sever-
al hundred underground nuclear explo-
sions set off in the same period radiated
seismic waves that could be mistaken
for those of an earthquake. Our experi-
ence indicates an extremely low proba-
RADIATION PATTERNS of the P waves resulting from an under-
ground explosion (left) and an earthquake (right) are compared. The
first motion of the P waves from an explosion is uniformly outward
and hence is generally observed as an upward displacement at all seis-
mic stations. The first motion of the P waves from an earthquake is
outward in some directions and inward in others; the pattern of the
waves at the surface depends on the orientation of the plane of the
earthquake fault. In the comparatively simple case of a vertical strike-
slip fault, shown here, the four-lobed radiation pattern observed at
the surface for both P waves and Rayleigh waves is a simple projec-
tion of the three-dimensional P-wave configuration. emanating from
the hypocenter of the earthquake. The radiation pattern of the Love
waves emitted by the same source is rotated by 45 degrees with re-
spect to the surface pattern of the P waves and the Rayleigh waves.
51
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bility that an event will'remain unidenti-
fied when all the available techniques of
discrimination are brought to bear.
N o monitoring technology can offer
an absolute assurance that even the
smallest illicit explosion would be de-
tected. We presume that an ability to
detect and identify events whose seismic
magnitude is equivalent to an explosive
yield of about one kiloton would be ad-
equate. It is often assumed that for the
U.S. to subscribe to a comprehensive
test ban it would require 90 percent con-
fidence of detecting any violation by an-
other party to the treaty. Developing a
new nuclear weapon, however, general-
ly requires a series of tests, and the prob-
ability that at least one explosion will be
detected rises sharply as the number of
the tests is increased. Moreover, a 90
percent level of confidence for the detec-
tion of even a single explosion probably
is not needed. For a country seeking to
evade the treaty the expected probabili-
ty of detection would certainly have to
be less than 30 percent, and perhaps
much less, even if only one illicit test
were planned. The test-ban agreements
that have been considered over the years
all include an "escape clause" through
which a country could renounce its trea-
ty obligations. Unless the probability
of detection were very low, a country
whose national interest seemed to de-
mand a resumption of testing would pre-
sumably invoke the escape clause rath-
er than risk being caught cheating.
Given these standards of reliability
for a monitoring system, it is possible to
specify the size and the sensitivity of the
ARCTIC EARTHQUAKE
SEPTEMBER 8, 1972 mb=5.9
P
T UP
DOWN
NUCLEAR EXPLOSION, U.S.S.R.
AUGUST 28, 1972 mb=6.3
TUP
IDOWN
seismic network that would be needed to
verify compliance with a comprehen-
sive test ban. Two kinds of network can
be considered for maintaining seismic
surveillance of the U.S.S.R. One net-
work consists of 15 stations outside the
borders of the U.S.S.R. In the second
network the 15 external -stations are sup-
plemented by 15 internal ones.
The ultimate limit on the detection of
seismic signals is imposed by micro-
seisms, or random vibrations of the
earth's surface. Most microseisms are
induced by the earth's atmosphere and
oceans. In order to detect a one-kiloton
explosion in much of the U.S.S.R. a
monitoring network would have to be
able to recognize above the background
noise any event with a short-period P-
wave magnitude of 3.8 or more. In or-
der to distinguish an explosion from an
earthquake by comparing the long-peri-
od magnitude with the short-period one,
the network would also have to be able
to detect surface waves with an Ms mag-
nitude.of 2.5 or more. The network of 15
external stations could achieve these
goals. Indeed, since almost all the seis-
mic areas of the U.S.S.R. are along its
borders, the external network would be
sensitive to events of even smaller mag-
nitude there. The mere detection of a
seismic event in most areas of the interi-
or would constitute identification of the
event as an explosion.
The lower limit of one kiloton on the
yield of an explosion that could be de-
tected by an external network is based
on the assumption that the coupling be-
tween the explosion and the seismic ra-
diation is efficient and that the explosion
1 MINUTE
SEISMOGRAMS OF LONG-PERIOD WAVES from an earth-
quake in the Arctic near the U.S.S.R. (top) and an underground nu-
clear explosion in the U.S.S.R. (bottom) were recorded at a seismic
station in Elath, Israel, roughly equidistant from the two events. The
short-period body waves generated by the two shocks were observed
to have almost the same magnitude. The magnitude of the long-peri-
od Rayleigh waves recorded in these traces, in contrast, is clearly
was not set off during or soon after a
large earthquake. If one must consider
the possibility that a country would try
to evade a test-ban treaty by decoupling,
or muffling, an explosion and thereby
reducing the amplitude of the emitted
seismic signals, an improved network
would be required. In principle such
muffling could be done by detonating
the explosion in a large cavity or by
using energy-absorbing material in a
smaller cavity. The former stratagem
might reduce the seismic signal of an
explosion by 1.9 magnitude units as
measured by one-second P waves (that
is, by mb). The latter stratagem might
bring a reduction of one unit.
The use of an oversize cavity is clearly
the more worrisome possibility, but it
could be attempted only in certain geo-
logic formations: a salt dome or a thick
sequence of bedded salt deposits. Few
areas of the U.S.S.R. have deposits of
salt in which the construction of a cavity
large enough for decoupling a several-
kiloton explosion would be possible.
The maximum size of a cavity that
could reasonably be constructed and
maintained sets a limit of.two kilotons
on explosions that might be muffled in
this way and escape detection by the
15-station external network.
Another way to reduce the amplitude
of radiated seismic waves is by detonat-
ing an explosion in a low-coupling medi-
um such as dry alluvium. The maximum
thickness of dry alluvium in the U.S.S.R.
sets a limit of 10 kilotons on explosions
that might be concealed by this means,
again assuming that only the 15 exter-
nal stations were installed.
111, Al
II
much greater for the earthquake than it is for the explosion. The ra-
tio of long-period surface waves to short-period body waves has been
shown to be a reliable criterion for distinguishing the seismic waves
of earthquakes from those of explosions. In addition the P wave of
the explosion has more high-frequency energy than the P wave of
the earthquake. The S wave of the earthquake is large, whereas that
of the explosion is small and not easily identified in the seismogram.
 Approved For Release 2007/02/28: CIA-RDP84BO1072R000300050002-0
Another possible drawback of an ex-
clusively external network should be
mentioned. Confusion could arise when
signals from two or more earthquakes
reached a station simultaneously. The
effect would be most troublesome when
the long-period waves from a small
event in the U.S.S.R. arrived.at the same
time as similar waves from a much larg-
er earthquake elsewhere in the world.
Under these circumstances it might be
difficult to establish with certainty by
comparing MS with Mb the identity of
the event in the U.S.S.R. With a network
of 15 external stations there would be a
few events per year in which the smaller
earthquake was in the territory of the
U.S.S.R. or within 25 kilometers of its
borders and at a depth of less than 50
.kilometers.
lmonitoring network made up of 15
seismographic stations outside the
U.S.S.R. and 15 inside it would large-
ly eliminate the problem of coincident
earthquake signals and would greatly
reduce the maximum yield of an explo-
sion that might escape detection, even if
decoupling were attempted. The inter-
nal monitoring stations would be simple
unattended ones, with the capability of
measuring vertical ground motion and
two orthogonal components of horizon-
tal motion, so that the distance and di-
rection of a nearby event could be esti-
mated from the data of a single short-
range station. With such a network in
place, and assuming that muffling was
attempted in the presence of normal
earth noise, the largest explosion that
would have a 30 percent chance of es-
caping detection in any setting except a
salt dome would be .5 kiloton.
For salt domes the main area of con-
cern in the U.S.S.R. is the region north
of the Caspian Sea. Our hypothetical
network has three stations there. Even
a small explosion in a large salt-dome
cavity would emit certain Pand S waves
with an amplitude large enough to be
detected by nearby stations. Further- detection by even one of the sta-
tions would immediately identify the
event as an explosion because the area
has no natural seismic activity. As a re-
sult evasion would not be likely to be
attempted at a yield greater than one
kiloton even in the salt-dome area.
A possible strategy for evasion that
has been mentioned from time to time is
the one of hiding the seismic signal of a
nuclear explosion in the signal of a large
earthquake, which might be near the site
of the explosion or far from it. For the
U.S.S.R. the only credible possibility is
a distant earthquake because the only
possible testing sites where earthquakes
are frequent enough to make the effort
worth while are on the Kamchatka Pe-
ninsula and in the Kurile Islands. Clan-
destine testing there is not likely because
seismic activity in the area can be moni-
? ? o
? e
?0
e? 0
?ooo ^
? 0 000 0 ? ?:?e
o 000 0 ? ? 00 0 0 0
? ?
? ? ? 00. 00 ? ^ O
?0 0 0 ?00e ?
? e
000 000 a 0e
Goo 00000 0
0 000 00 0
?0
??^ ^ +
+ ^
0.Z~ffl+ ^ ^ +
0^o Offl-
ffl +
4 4.5 5 J
5.5 6 6.5 7
MAGNITUDE OF ONE-SECOND BODY WAVES (mb)
CLEAR DISTINCTION between earthquakes and explosions is evident in this plot of the
magnitude of long-period surface waves (MS) against that of short-period body waves (mb).
The 383 earthquakes represented by the black dots were compiled from a set of all the earth-
quakes recorded worldwide in a six-month period that had an Mb value of 4.5 or more and a
focal depth of less than 30 kilometers. (There are fewer dots than earthquakes because the
magnitudes of some of them coincided.) The colored squares designate underground explosions
in the U.S. and the colored crosses underground explosions in the U.S.S.R. Only one earthquake
falls within the explosion population, as defined by the straight line separating the two groups
of events. This single event, which had the smallest magnitude of any of the earthquakes in the
survey, took place in the southwest Pacific Ocean, a region where the sensitivity of the net-
work of seismic stations is poorer than it is in most of the Northern Hemisphere. The mb values
were adjusted to take into account regional variations in the amplitudes of short-period waves.
DEPTH . 50 KM.
LOCATION > 25 KM. AT SEA
DEPTH , 30 KM.
Ms:mb
DEPTH -- 50 KM.
Ms:mb
LOCATION > 25 KM. AT SEA
DEPTH a 30 KM.
MS:mb
LOCATION > 25 KM. AT SEA
0 200 400 600 800
EVENTS IDENTIFIED AS EARTHQUAKES
METHODS OF DISTINGUISHING earthquakes from explosions were tested by applying
the methods to all the earthquakes with a magnitude of 4.5 or more recorded during a 162-day
period in 1972. The sample consisted of 948 events. Many of them could be classified as earth-
quakes (rather than explosions) by their location or their depth. The remaining events could be
classified by comparing the magnitude of long-period surface waves with the magnitude of
short-period body waves (the ratio MS: mb). The sequence in which the tests were applied af-
fected the efficiency of the procedure, but all events were identified regardless of the sequence.
 Approved For Release 2007/02/28: CIA-RDP84BO1072R000300050002-0
tored'in detail "from'stations in Japan
and the Aleutian Islands. Indeed, ocean-
bottom seismometers and hydroacous-
tic sensors could be placed just offshore.
The first defense against evasion by
the masking of a test in a large earth-
quake is the questionable feasibility of
the subterfuge. Unless the evader main-
tained several testing sites the number of
opportunities per year for clandestine
testing would be quite limited. In addi-
tion the evader would have to maintain
his weapons in constant readiness for
firing. To attain the evasion capability
given below he would have to set off an
explosion within 100 seconds of the time
of arrival of the short-period waves of
the earthquake. He would have to esti-
mate the maximum amplitude and the
decay rate of the earthquake waves with
high accuracy, and he would have to be
certain of the amplitude of the P waves
generated by the explosion to within .1
magnitude unit. Even after taking these
precautions the evader would have to
accept a high probability that the event
would be detected by at least one mon-
itoring station and a small probability
that three stations would detect it. He
would also have to install and operate
his testing site (including a large cavity)
and his own seismological network in
total secrecy over a period of years.
In contrast to these daunting require-
ments for successful evasion, the only
requirements for a monitoring nation
are to operate a network of high-quality
seismic stations and to process the data
with determination. Against a network
of 15 external stations and 15 internal
ones the only effective evasion schemes
at yields of one kiloton or more would
require both decoupling and hiding the
explosion signal in an earthquake.
he issues relating to the monitor-
Ting of a comprehensive test ban can
be summarized as follows. The under-
standing of seismology and the testing
of seismometer networks are sufficient-
ly complete to ensure that compliance
with a treaty could be verified with a
high level of confidence. The only explo-
sions with a significant likelihood of es-
caping detection would be those of very
small yield: less than one kiloton provid-
ed the monitoring system includes sta-
tions in the U.S.S.R.
It is important to view the question of
yield in the context of the nuclear weap-
ons that have been tested up to now.
The ones that ushered in the nuclear
age in 1945 had a yield of from 15 to
20 kilotons. Yields increased rapidly to
the point where the U.S.S.R. tested
a 58,000-kiloton weapon in 1961. The
largest underground explosion had a
yield of almost 5,000 kilotons. Unclassi-
fied reports place the yield of the weap-
ons carried by intercontinental missiles
in the range from 40 to 9,000 kilotons.
The yields of underground explosions
that might go undetected or unidentified
under a comprehensive test ban are
therefore much smaller than those of
the first nuclear weapons. If the thresh-
old of reliable detection and identi-
fication is one kiloton, that is only
one-150th of the limit specified by the
Threshold Test Ban Treaty of 1976.
From the viewpoint of verification a
comprehensive test ban would actually
establish the equivalent of a very low
threshold, since weapons of extremely
low yield could be tested underground
without the certainty of being detected
and identified. A treaty that imposed a
threshold near the limit of seismological
monitoring capability might therefore
be considered an alternative to a com-
prehensive test ban. Such a treaty might
be preferable to the present quite high
threshold, but it would have the dis-
advantage that arguments could arise
over the exact yield of tests made near
the threshold. Indeed, the judgment of
whether or not a test has taken place will
always be less equivocal than an exact
determination of yield.
In recent years there have been re-
ports that the U.S.S.R. may have repeat-
edly violated the 1976 treaty by testing
devices with a yield greater than the
150-kiloton limit. Such reputed viola-
tions were recently cited as evidence
that the threshold treaty, which has not
been ratified by the U.S. Senate, is not
verifiable and should be renegotiated.
On the basis of our analysis we conclude
that the reports are erroneous; they are
based on a miscalibration of one of the
curves that relates measured seismic
magnitude to explosive yield. When the
correct calibration is employed, it is ap-
parent that none of the Russian weapons
tests exceed 150 kilotons, although sev-
eral come close to it.
Observations at the Nevada Test Site
(NTS), where American nuclear-weap-
ons tests are held, indicate there are lin-
THRESHOLDS OF DETECTION for seismic events in the Eastern
Hemisphere are delineated by the two sets of contours drawn on this
pair of maps for a proposed network of 15 seismic stations established
outside the U.S.S.R. Colored dots give the location of 12 of the 15 sta-
tions; three others are off the maps. The number on each contour in-
dicates that an event of that magnitude or larger has at least a 90
percent probability of being detected by four or more stations. The
contours on the map at the left represent the detection thresholds for
short-period body waves and those on the map at the right the detec-
tion thresholds for long-period surface waves. On these maps and the
ones on the opposite page the only seismic noise taken into account
is the microseismic noise generated by the atmosphere and oceans.
C.1
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 Approved For Release 2007/02/28: CIA-RDP84BO1072R000300050002-0
IMPROVED DETECTION THRESHOLDS for seismic events in
the Eastern Hemisphere are delineated by the two sets of contours
drawn on this pair of maps for a proposed network of 30 seismic sta-
tions: 15 outside the U.S.S.R. and 15 inside. For most of the U.S.S.R.
the effect of adding the 15 interior stations would be to lower the de-
ear correlations between the logarithm
of the explosive yield and the two mag-
nitude values, Ms and mb, for explo-
sions with yields greater than 100 kilo-
tons. When the measured Ms and Mb
values of explosions at the Russian test
site near Semipalatinsk are inserted into
the NTS formulas, however, the result-
ing estimates of yield given by Mb are
more than four times as great as those
given by Ms. For explosions in hard
rock at many test sites estimates of yield
based on the NTS Ms formula have
invariably agreed with actual yields,
whereas estimates based on the NTS mb
formula have sometimes been in drastic
disagreement with the actual yield.
A strong correlation has been found
between Mb values measured at individ-
ual stations and P-wave travel times to
these stations. The U.S.S.R. routinely
publishes seismological bulletins that
include P-wave arrival times of earth-
quakes, and it is straightforward to in-
terpret the times-for stations in central
Asia in terms of the expected pattern of
Mb values near Semipalatinsk. From an
analysis of the P-wave signals it is pre-
dicted that the Mb value for an explosion
at Semipalatinsk is 40 percent greater
than an equivalent explosion at NTS.
This is the same correction that must be
applied to the curve relating Mb to yield
at NTS to make the Mb estimates of the
yield of Russian explosions consistent
with the Ms estimates. Thus two modes
of analysis lead to the conclusion that
there is an essentially universal relation
between Ms and yield whereas the curve
relating Mb to yield must be calibrated
for each test site.
tection threshold for short-period body waves from a magnitude of
3.8 to one of 3.4 (left); the corresponding effect for long-period sur-
face waves would be to lower the detection threshold from a magni-
tude of 2.6 to one of 2.3 (right). The interior stations would also pro-
vide more accurate information on the focal depth of a seismic event.
A comprehensive treaty would have
an additional advantage over a low-
threshold treaty: all technological un-
certainties would work against the po-
tential evader. A country planning a sur-
reptitious nuclear test could not know
the exact seismic-detection capability of
other nations or the exact magnitude of
the seismic waves that would be gener-
ated by his test. A ban on nuclear explo-
sions of all sizes would also have the
important conceptual value that nucle-
ar weapons, no matter what their size,
would be recognized as inherently dif-
ferent from conventional weapons.
I t is sobering to consider how the
state of the world would differ if a
full test ban had been achieved in 1963.
The number of nuclear weapons has
grown tremendously since then and is
now estimated at from 50,000 to 100,-
000. The loss of life. and the social dam-
age that would be inflicted in a ma-
jor nuclear exchange are vastly greater
than they were in 1963. Furthermore,
both the U.S. and the U.S.S.R. are less
secure now than ever before, not be-
cause of any failure to develop arms but
because of the growing stockpiles of
weapons and the inability of any nation
to defend itself against nuclear attack.
A comprehensive test-ban agreement
should not be regarded as a substitute
for disarmament. Meaningful reduc-
tions in the nuclear threat must include a
continuing and serious process of arms
control; in this process, however, a com-
prehensive test-ban treaty could have an
important part. The problems of negoti-
ating such a treaty are overwhelmingly
political rather than technical and must
be recognized as such.
Before the suspension of negotiations
between the U.S., Britain and the
U.S.S.R. in 1980 tentative agreement
had been reached on a number of issues.
All three nations agreed that a test-ban
treaty would include a prohibition of
all tests of nuclear weapons in all en-
vironments, a moratorium on peaceful
nuclear explosions until arrangements
for undertaking them could be worked
out, provisions for on-site inspections,
a mechanism for the international ex-
change of seismic data and the installa-
tion of tamperproof seismic stations by
each country in the territory of the oth-
ers. The proposed treaty would have
a term of three years. The agreements
on the long-standing issues of on-site
inspection, peaceful explosions and
the placement of monitoring stations
in each country represented important
breakthroughs. It would be a setback for
the cause of international security if this
hard-won ground were now lost.
For many years the stated policy of
the U.S. has emphasized the desirability
of a complete test ban if verification
could be ensured. The policy was not
fundamentally altered by the recent de-
cision of the Reagan Administration to
put off further negotiations on the test
ban. On the contrary, it was reported
that the Administration still supports
the ultimate goal of a comprehensive
ban on nuclear testing but has doubts
about the efficacy and reliability of seis-
mic methods of verification. As we have
attempted to show here, there can be no
substance to such doubts.
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