The paper below is slightly revised from the version appearing on pages 53 to
81 of a book published in 1996.
[An
abstract is included here but not in the book; and Figure 2 now includes some
discussion of the actual monitoring networks built in support of the CTBT whose
text was agreed to in 1996, after preparation of the book in which the original
paper appeared.]
The formal reference for the book in which the original article appeared is:
Monitoring
a Comprehensive Test Ban Treaty
by
E.S. Husebye and A.M. Dainty (eds.), from Kluwer Academic Publishers,
Dordrecht, The Netherlands, 836 pages, 1996.
This
paper is not intended as a review of current capability to monitor nuclear
explosions. For such a review, see
reference 41 below (written mostly in the year 2000 and published in 2002).
SEISMOLOGICAL
METHODS FOR MONITORING A CTBT:
THE TECHNICAL ISSUES ARISING
IN EARLY NEGOTIATIONS
PAUL G. RICHARDS1 and JOHN
ZAVALES2
1Lamont-Doherty Earth Observatory, and Department of
Earth and Environmental Sciences, Columbia University,
Palisades, New York 10964, USA.
2US Department of
Defense, Office of Humanitarian and Refugee Affairs
Abstract
Intensive efforts to negotiate a
Comprehensive Test Ban Treaty were carried out from 1958 to 1963, resulting in
the Limited Test Ban Treaty banning nuclear tests from the atmosphere,
underwater, and in space. Underground nuclear explosions were not banned, in
part because seismological methods for monitoring the underground environment
were thought to be inadequate. Over the subsequent 30 years, more than 1500
nuclear tests were carried out underground. They showed that seismological
methods of monitoring a CTBT were far better than had been thought in early
treaty negotiations, and, by the late 1960s, met the level of monitoring
capability desired in 1963. Had the global monitoring system advocated in 1958
been built, its capabilities would have far exceeded the capability then said
to have been necessary for a CTBT.
1. Introduction
The most important technical issues
in monitoring a Comprehensive Test Ban Treaty all became apparent between 1958,
when the so-called Conference of Experts was convened in Geneva, and 1963, when
the Limited Test Ban Treaty (LTBT) was negotiated, signed, ratified, and put
into effect. The LTBT was negotiated trilaterally, between the United States,
the Soviet Union, and the United Kingdom; and banned nuclear testing in space,
in the atmosphere, and under water. But in 1963 there was a general perception
that seismological methods for monitoring underground nuclear explosions were
inadequate — a perception that helped strongly to prevent the conclusion of a
Comprehensive Test Ban Treaty (CTBT) in this period, even though the key
leaders (Presidents Eisenhower and Kennedy for the US, General Secretary
Khrushchev for the USSR, and Prime Minister Macmillan for the UK) apparently
favored a comprehensive ban and made numerous proposals on how it might be
implemented and verified.
In the words of a former Director of the Los Alamos National Laboratory, Dr.
Donald M. Kerr, "Nuclear weapon testing is ... a process intimately
intertwined with the design of nuclear weapon systems [1]."
In the three decades following the unsuccessful CTBT negotiations of the early
1960s, over 1500 underground nuclear tests were carried out by the US, the
USSR, France, the UK, China, and India; that is, about one nuclear test a week,
for thirty years. Though the great majority were single explosions, more than a
hundred of the tests consisted of more than one nuclear explosion. This
extensive activity shows that nuclear weapons development, at least by the
superpowers, was not been constrained by the LTBT.
Very few underground tests had been carried out, at the time of the early CTBT
negotiations. Indeed, only one such test had occurred prior to the 1958 Geneva
meetings. Early conclusions on the capability of seismological methods to
monitor a CTBT were therefore reached on the basis of minimal data, at a time
when seismology itself was practiced at only a few tens of institutions around
the world. Seismic data then consisted usually of paper records, rarely seen
outside the institution that owned them; were derived entirely from earthquakes
or small chemical explosions; covered only a narrow range of frequencies; and
had low dynamic range so that it was not possible to record both strong and
weak signals on the same instrument.
The perceived failure of seismology to support a major arms control objective —
the CTBT — coupled with the need to acquire information on foreign underground
nuclear weapons tests, led the US and the USSR in about 1960 to begin new
efforts in instrumentation and research. These efforts hastened the development
of seismology over more than a decade, turning it into the modern quantitative
science we know today.
This paper first reviews the key technical issues in CTBT verification that
emerged in politically charged negotiations up to 1963, and comments upon the
conclusions concerning monitoring capability reached by the US at that time. In
a later section, the key technical issue not developed prior to 1963 (namely,
event identification) is briefly reviewed in light of later practical
experience. The underlying question throughout is not only: How are underground
nuclear explosions detected and identified? We also ask: How did our present
understanding of these issues evolve? By the late 1960s, seismological
monitoring methods had improved to reach the level of CTBT verification
capability desired by the U.S. in 1963, even though the global monitoring
network advocated in 1958-60 was never built. Had it been built, monitoring
capability would have been improved about tenfold over what was desired by the
U.S. in 1963.
2. History of the Treatment of CTBT Verification, 1957-1963
The failure of post-World War II efforts to develop some type of international
control over atomic weapons, and the subsequent development of the hydrogen
bomb, resulted in substantial programs of atmospheric nuclear weapons testing.
In 1954, fallout from the US 15 megaton BRAVO test contaminated a Japanese
fishing boat, causing the death of one man and the serious illness of several
others. Later that year, radioactive debris from a Soviet test fell over part
of Japan. Many physicians and biologists, able to observe the long-term medical
effects of the Hiroshima and Nagasaki bombings, charged that atmospheric tests
would carry radioactive material worldwide, causing a genetic hazard that would
be particularly damaging if cumulative doses occurred from fallout.
The dangers of fallout thus became the first rationale for a test ban, with
proponents such as Linus Pauling, the 1954 Nobel Prize winner in chemistry,
predicting that more people would die of cancer if atmospheric testing
continued unchecked; and opponents such as Edward Teller, a promoter of nuclear
weapons development, concluding that cigarette smoking would shorten lives far
more than fallout. At this time Edward Teller and Ernest Lawrence, of the
Livermore Radiation Laboratory, sought to separate the fallout and testing
issues by speaking of a 95% clean hydrogen bomb, whose fallout would be
negligible. However, such a device would have to be detonated very high in the
atmosphere to minimize fallout, and would have to be of very high yield, relative
to the size of its fission trigger, to approach the 95% claim [2].
In February 1955 the US Atomic Energy Commission published a report on fallout
and its consequences, which was widely criticized as a biased justification of
nuclear testing [3, p. 140].
By the mid-1950s both superpowers realized the need for discussion, at least,
of a prohibition on nuclear weapons testing. However, they differed
significantly on how a test ban might be implemented. Initially the Soviets
favored an agreement to outlaw tests, preceded by a complete testing
moratorium, before a control system to monitor the agreement was established.
Because such a system could entail intrusive on-site inspections, they claimed
that inspections with no prior treaty commitment would aid US espionage efforts
and undermine Soviet security. The United States preferred the establishment of
formal controls prior to the signing of an agreement. It was believed in the
West that without such controls the more restrictive nature of Soviet society
might permit clandestine testing, and consequently a lead over the US in weapon
development. However, at the 1957 meeting of a Subcommittee of the Disarmament
Commission of the UN, conducted in London, the USSR surprisingly announced that
it would agree to establishing a control system with posts in the USSR, US, UK,
and somewhere in the Pacific Ocean, prior to the signing of a test ban
agreement. Furthermore, the Soviets announced they would accept a temporary
moratorium on tests, two to three years in length. Most importantly, the
Soviets accepted a British suggestion that the Subcommittee establish technical
working groups to study the feasibility of limiting tests and monitoring such
an agreement. At this time, it should be noted, the USSR proposed a nuclear
test ban as an objective unto itself, while the Western powers favored a test
ban only as a first step to some type of general disarmament agreement [4, p.
16].
Two events, occurring far from the negotiating table, rendered the test ban
debate more urgent. Thus, on September 19, 1957, the US carried out the world's
first underground nuclear explosion in which the radioactive by-products were
fully contained. This was the 1.7-kiloton RAINIER test on the Nevada Test Site.
Quoting from Dr. Gerald Johnson [5], writing of his experience when in charge
of the nuclear test program for Livermore: "The development of the
technique of underground testing was stimulated in the latter 1950s because of
rising concerns about radioactive fallout both locally and worldwide from
atmospheric testing. These concerns were brought forcibly to my attention in
1956 ... when we experienced delays of up to three weeks awaiting favorable
wind patterns which would result in acceptable local fallout." Second, on
October 4, 1957, the Soviet Union launched the world's first artificial
satellite, Sputnik I, an event that galvanized the US scientific community. In
November, Eisenhower established the President's Science Advisory Committee,
under the leadership of James Killian of MIT. The PSAC contained many men who
opposed the unlimited testing and development posture of the Department of
Defense and the Atomic Energy Commission. Foremost among these was Hans Bethe.
During the difficult Geneva negotiations of the following year, the PSAC was to
provide Eisenhower with views drastically different from those of Teller and
other prominent US advisers.
Early in 1958 Killian appointed an inter-agency committee, including
representatives of the PSAC, AEC, and DOD, to study the technical feasibility
of monitoring a test ban. This panel, chaired by Hans Bethe, reported in April
that a system of 24 inspection stations in the USSR, supplemented by mobile
inspection teams, could detect underground explosions down to a yield of one or
two kilotons. The panel also concluded that the risks to the US in being
subjected to such a test ban would be small, while the political advantages
were large; and that continued nuclear testing by both powers would rapidly
erode the technological lead the US enjoyed over the USSR.
Note that the only signals at the disposal of the Bethe Panel from an actual
nuclear explosion in what was perceived to be the most difficult environment to
monitor — namely, underground — was from the RAINIER test conducted six months
earlier. Note too that although judgments were made on the political ramifications
of a test ban, no political scientists or diplomats were members of the Panel.
The problem, which persists in test ban debates to this day, was that technical
experts were called upon to address issues that were essentially political in
nature. The difficulty arises, when the evaluation of technical capabilities
(and associated uncertainties) turns into a review of whether such capabilities
are in some sense acceptable — which is ultimately a political question. Test
ban opponents were quick to highlight these shortcomings of the Bethe Panel,
and Teller also emphasized that the Panel had completely ignored the study of
intentional evasion by one side.
The level of technical discussion of the RAINIER data reached a low point when
the AEC publicly announced that seismic signals from this shot were detected to
a maximum distance of only 250 miles (400 km). After an outcry from
knowledgeable scientists, the detection estimate was revised to 3700 km because
of an observation in Alaska. However, inspection of the seismogram in question
shows that during a 24-hour period it contained numerous detections with
amplitude comparable to that from the RAINIER explosion. Today, we would speak
of this as a problem not just in detection in the context of signal-to-noise ratios, but also in association. Given the level of seismic activity around the globe
(with approximately ten earthquakes a day having seismic waves comparable in
size to those from RAINIER), and the numerous instruments now deployed to
record seismic signals, it is necessary not only to detect signals, but to form
the correct subset of detections from different stations for a common seismic
event — whether earthquake or explosion — before proceeding to analyze the set
of detections, for example to estimate the location of the source.
The controversy over the Bethe Panel's findings coincided with an announcement
of the Supreme Soviet on March 31, 1958, that the USSR would discontinue all
nuclear tests providing the US and the UK followed suit. Nine days before, the
Soviets had concluded a very extensive test series, in the course of which two
or three explosions were often conducted in a single day. The US, having
scheduled to commence a test series in several weeks, was awkwardly placed.
Sensing a public relations ploy, Eisenhower dismissed the Soviet announcement
as a gimmick, which ought not to be seriously considered [6].
Letters ensued between Eisenhower and General Secretary Khrushchev, and on
April 8 Eisenhower proposed a meeting of technical experts, as envisioned at
the London Conference, a proposal which Khrushchev initially rejected on the
grounds that the conclusion of a test ban was a political, not a scientific,
matter. Eisenhower reiterated the need for technical meetings on April 28, in a
statement of some import: "Studies of this kind are the necessary
preliminaries to putting political decisions actually into effect [4, p.
50]." Some confusion existed in the interpretation of this sentence. The
Soviets believed it defined the technical meetings as formalities, subsidiary
to the inevitable conclusion of the treaty. The US interpretation was that the
technical talks were meant to explore the feasibility of concluding a treaty in
the first place.
Khrushchev accepted the scheduling of these talks on May 9, and the Conference
of Experts (to Study the Possibility of Detecting Violations of a Possible
Agreement on the Suspension of Nuclear Tests) convened on July 1, 1958 in
Geneva. Although conducted at United Nations facilities, the Conference was not
a UN-sponsored activity.
The American delegation consisted of James Fisk (Chairman), Robert Bacher, and
Ernest O. Lawrence (who returned to the US due to illness in the middle of the
conference and died of chronic colitis shortly thereafter). A group of about a
dozen physicists and seismologists was on hand to advise the delegates. The
only US State Department representatives were three observers of relatively
junior rank, whereas the Soviet delegation, headed by Yevgeni Federov, included
one very high ranking diplomat, Semyen Tsarapkin of the Collegium of the
Ministry of Foreign Affairs. The difference in composition of the panels
highlighted contrasting attitudes regarding the Conference and its eventual
goals.
The Conference first discussed detection and identification in four
environments: the surface and atmosphere of the Earth; underwater; in space;
and underground. Panelists generally agreed that tests in the first category
could be readily detected by their output of acoustic and radio waves and
radioactive debris, and oceanic tests could be easily detected with
hydroacoustic waves. It was agreed that when an underground test is conducted
at a depth sufficient to prevent radioactive debris from reaching the surface,
signals produced by seismic waves were the only means of detection.
Although there are several different seismic waves, in these early years only
the fastest seismic wave was given detailed consideration. This wave, known as
the P-wave (the P standing for primus, since it is the first wave to arrive at a distant
station), spreads though the Earth's deep interior in much the same fashion
that a pulse of sound moves through air. In air, the source of the sound might
be an exploding firecracker. In the Earth, the source of P-waves might be an earthquake or an underground
nuclear explosion. If enough instruments at different locations record the
arrival time of the P-wave from a
particular source, it then becomes possible to estimate the source location.
Throughout the five years leading up to the LTBT of 1963, it appears with few
exceptions that only P-waves were
considered for use in event identification.
The experts in 1958 found few problems with detection by electromagnetic and
hydroacoustic waves. A plan for airborne collection of radioactive debris was
eventually worked out, in which aircraft belonging to the nation being
overflown would be used, representatives of all the signatories would be on
board, and the flight path would be determined in advance.
The issue of underground detection was far more complex. The only empirical
data available at this time was for the RAINIER test. The Soviet delegation was
in general optimistic, and held that theoretical interpretation of data from
TNT explosions would be sufficient to determine monitoring capabilities for
underground nuclear explosions. The Americans replied that the RAINIER data
were not consistent enough to allow useful extrapolation.
After discussing detection methods, the Conference next turned to the
monitoring system that would be necessary. Federov immediately proposed a
system of 100 to 110 control posts, the spacing of which would be based on
acoustic detection of atmospheric tests. The Soviets maintained that the
existing network of seismographic stations for earthquake identification would
suffice to monitor underground tests.
The British and Americans rejected this proposal, arguing that existing
seismographic stations were not adequate for the task, and could serve only as
a supplement to a future system of new seismographic stations or control posts.
The only criterion for distinguishing earthquakes from explosions accepted at
this time was the "first motion" method, based on the expectation
that all explosions would be accompanied by a positive first motion (compression),
resulting in upward movement of
the surface of the ground at all distant monitoring stations when the P-waves arrived, while earthquakes would feature
negative first motion (rarefaction), or downward movement of the ground, at least at some stations. The
Western experts argued that in most stations the switching of a few wires would
reverse the recorded polarity of the first motion and make a compression appear
to be a rarefaction. Thus, relying on many stations manned by the potential
violator nation would be unacceptable.
It was recognized that the size of the seismic monitoring system was
inextricably linked to the desired threshold, above which events could be not
only detected but also identified as an earthquake or an explosion. The Western
delegates estimated that seismographic systems already in place could detect
and identify 5% of events equivalent to a one kiloton yield and up, 50% of 5 kt
and above, and 90% of 20 kt and above [7, p. 26].
The job of developing a US counterproposal on the size of the monitoring system
was entrusted to two young physicists, Richard Latter of the RAND Corporation
and Harold Brown of the Livermore Laboratory. The criterion they proposed was
observation of first motion at five different seismographic stations. Advocating
a capability of detecting and identifying 90% of events equivalent to
explosions of one kiloton and up, they concluded that a global network of some
650 stations would be necessary. Although these findings were presented merely
as a report, not as a formal proposal, Federov indicated that such a control
system would be unacceptable to the USSR.
Sir William Penney, head of the British delegation, proposed a third system. In
its detection capability Penney's system was a compromise between the US and
Soviet models. He suggested 160 to 170 land-based control posts, each operating
a small array of about 10 seismographic stations of which 100 to 110 would be
based on continents, 20 on large islands, and 40 on small islands, although the
precise locations were not specified. Ten ships equipped to detect atmospheric
and oceanic tests would supplement these posts. Penney believed [7, pp. 26-35]
that such a system would detect and identify 90% of the earthquakes equivalent
to 5 kilotons or more, and a small percentage of those equivalent to one
kiloton. The other 10% of 5 kt-equivalent events would have to be inspected,
and estimates of the number of such events ranged from 20 per year (USSR
estimate) to 100 per year (US estimate).
The Penney system was in general well received, and the Conference concluded on
August 21 after both groups agreed to recommend a system based on Penney's
proposal. One important issue was left unresolved. The West suggested that all
suspicious unidentified events lead to on-site inspections, while the Soviets
favored individual decisions on each case by the control commission, with each
member nation having veto power.
Many observers believed that, by obtaining agreement on Penney's proposal, the
USSR had maneuvered the US into agreeing to a test ban. Critics such as Teller
contended that the limitations of the system were not strongly presented, and
the idea of deliberate evasion was not discussed. In the contest between the
bootlegger and the police, Teller wrote, the bootlegger has a great advantage
[8]. He and many other critics believed the Conference of Experts constituted a
Soviet propaganda victory [9].
Nonetheless, the US government, especially the State Department, felt compelled
to make a public statement demonstrating its commitment to eventual test
cessation. President Eisenhower proposed on August 22, 1958, that formal
negotiations begin on October 31.
He announced that the US would refrain from testing for a period of one
year from the start of these talks unless the Soviets resumed tests. He went on
to say that such a moratorium could be extended, subject to the installation of
a control system and satisfactory progress in implementing other arms control
measures.
General Secretary Khrushchev, while criticizing the proposition for limiting
the moratorium to one year and for its two accompanying conditions, accepted
the October 31 date for beginning negotiations. In the intervening two months
the USSR, US, and UK each undertook an extensive series of nuclear tests.
The diplomatic negotiations, again conducted in Geneva, began on October 31,
1958, but three weeks were consumed in a dispute over the formal conference
agenda, until the delegates gave up and proceeded without such an agenda. Even
the title of the talks, The Conference on the Discontinuance of Nuclear Weapons
Tests, was in dispute, with the USSR equating discontinuance with cessation,
and the West interpreting it to mean suspension.
After several weeks the USSR introduced a draft treaty of five short articles.
It bound the three powers not to undertake nuclear tests in any medium, and to
discourage the commencement of nuclear testing by all other states in the
world. Compliance would be verified through the detection network recommended
by the Conference of Experts.
The Western delegates rejected the draft on grounds that no mention was made of
other disarmament measures, no control organization was specified, and no
provision was made for sanctions against violators. Furthermore, the American
and British negotiators were still less than fully confident in the
capabilities of the Geneva System of the Conference of Experts. After several
more weeks the USSR agreed to the inclusion of a control commission provision,
although the exact composition of such a body remained in dispute when the
negotiations recessed on December 19.
Upon the resumption of talks on January 5, 1959, the chief US delegate, James
Wadsworth, held an informal meeting with his Soviet counterpart, Semyen
Tsarapkin. He informed him that in the course of underground tests conducted in
Nevada in October 1958, data were obtained which indicated that the detection
of tests would prove more difficult than previously believed. Based on these
tests, known as the HARDTACK II series, it appeared that the number of
earthquakes equivalent to a given explosive yield would be far greater than
earlier estimates, perhaps by a factor of ten to fifteen. In addition, better
data on background noise indicated that the first motion would be more
difficult to determine accurately. These findings meant, according to
Wadsworth, that the 90% confidence identification threshold proposed in the
Geneva System would be more on the order of 20 kt than 5 kt, and that a far
larger number of control stations would be required to maintain the 5 kt
threshold.
In the next few weeks other ideas were put forward which further dampened hopes
of concluding a treaty. Carl Romney, a seismologist for the US Air Force,
stated in congressional testimony that, based on HARDTACK data, the number of
earthquakes indistinguishable from 5 kt explosions would not be 20 to 100 per
year, as estimated at the Conference of Experts, but probably 700 to 3000, of
which 100 to 500 would be in the USSR and China [10]. Romney's 1959
congressional testimony on monitoring capability marks one of those points in
the early CTBT debates where the technical assessments offered to policy makers
turned out in retrospect to be way off track. As became apparent by the early
1970s, the number of earthquakes indistinguishable from 5 kt explosions in the
USSR and China were few in number — in fact, approximately zero per year, not
100 to 500. Romney's summary statement drew upon answers to several separate
technical questions, such as:
How many earthquakes occur each year at different magnitude levels?
What would be the magnitude levels down to which a hypothesized global network
of seismographic stations could achieve reliable detection and identification?
What was the relationship between the yield of an underground nuclear
explosion, and its seismic magnitude?
In each of these areas, Romney's 1959 testimony offered numbers quite different
from what was discovered and accepted in later years. Thus, he concluded there
were about 20,000 earthquakes worldwide, each year, whose seismic magnitude was
4 or greater. Today, we would give about 7500 for this number [11]. He
concluded that what today would be considered a dense global network (the
Penney proposal) could supply reliable detection only down to the magnitude range
of about 4 to 4.5. Today, we would give about 3 to 3.5 for this magnitude
range, even with a less dense network (paper CD/1254, of the Conference of
Disarmament). In this early period he was apparently using the relation [12,
Fig. 15]:
m = 3.9 +
(2/3) log Y (in kt),
which gives a
yield (Y) of about 19 kt
corresponding to a magnitude (m)
of 4.75, whereas this magnitude was later found to correspond to about 10 kt
for a typical underground explosion in wet tuff at the Nevada Test Site (see
[13], which in 1981 reported the relation for this test site as m = 3.92 + 0.81 log Y); and to only 2.5 kt for a typical explosion at what
became the USSR's main test site (see [14], which in 1992 reported m = 4.45 + 0.75 log Y for the Balapan area of the Semipalatinsk Test Site).
Going back to our historical review, several points should be noted in
connection with the HARDTACK data. Out of eight underground explosions included
in the series, only two, BLANCA (19 kt) and LOGAN (5 kt) produced seismic data
sufficient for evaluation of system capabilities. US seismologists also
concluded that the previous magnitude estimate for the 1957 RAINIER test was
too high because the seven best stations near the event had given what now
appeared to be anomalously large results. Thus, RAINIER, known to be 1.7 kt in
yield, should have been estimated at magnitude 4.06 (± 0.4) and not 4.25 (±
0.4) as previously believed. In addition, difficulty in assessing signs of
first motion in the HARDTACK tests indicated that the ratio of first motion to
background noise amplitude must be at least 3 to 1, rather than 2 to 1 as
estimated earlier [15].
Just as the significance of HARDTACK was being debated, a theory even more
discouraging to test ban advocates emerged. Albert Latter, of the RAND Corporation,
presented preliminary findings on the principle of cavity decoupling — the
explosion of a bomb in an underground cavity large enough that the surrounding
rock would not deform plastically (permanently) in any direction, but remain
elastic. Under such conditions, according to Latter, the seismic signal could
be reduced by a factor of as much as 300, thereby rendering impossible the
detection of all but the very largest tests [16].
The controversy surrounding HARDTACK and cavity decoupling led James Killian,
the President's Special Assistant for Science and Technology, to appoint a
Panel on Seismic Improvement, chaired by Lloyd Berkner. The Berkner Panel, in a
report on March 16, 1959, concluded that, given current technology, an increase
in the number of seismometers at each array station from 10 to 100 would make
detection of the first motion much easier. The panel also recommended the
establishment of supplementary unmanned stations, 170 km apart in seismic
areas, which could identify 98% of one-kiloton events. Future improvements were
discussed, including the use of seismometers in deep boreholes, an extensive
chemical explosive testing program, and computer-aided reconstruction of
waveforms. Regarding cavity decoupling, the Berkner Panel reached a less
pessimistic conclusion than Dr. Latter, and stated that apparent yield could
probably be decreased ten-fold, depending on the surrounding rock type [17].
The Berkner Panel also recommended major funding for research in basic
seismology, with particular attention to improvements in data acquisition.
Thus, a key recommendation was that 100-200 of the existing stations in the
world be equipped with modern instruments as soon as possible. Annual budgets
of about $18 million were outlined for such improvements, plus another $12
million for each of two years to carry out chemical and special nuclear
explosions underground for monitoring research [18]. Since, prior to 1960, the
field of pure seismology in the United States had received national support at
the level of only about $0.7 million annually [19, p. 80], and since funding at
the level recommended by the Berkner Panel (for seismology not for nuclear
explosions) was actually appropriated and spent [19, pp. 27-37], verification
research has had an enormous impact on seismology — and on geophysics in
general.
In 1959, many feared these new US reports would cause the Geneva talks to
collapse. The Soviets refused to consider the HARDTACK data on procedural
grounds, namely that the seismometers used were not identical to those
specified in the Conference of Experts. The US responded that in a study of
small chemical explosions the HARDTACK seismometers had outperformed the
Geneva-specified equipment. Decoupling theory was greeted with outrage on the
part of the Soviets, who asked why a nation serious about concluding an
agreement should devote time and money to devising means of circumventing it.
Torn between his own desire for a test ban and this new evidence, Eisenhower
proposed on April 13, 1959, a treaty to ban only policeable tests, defined as
those in the atmosphere up to 50 km and in the ocean. Khrushchev vehemently
rejected the suggestion, claiming that the US would continue nuclear testing
underground and in space; and that, in any event, all tests were policeable.
Despite their reservations, the Soviets agreed to the establishment of
Technical Working Group I, in the summer of 1959, to study high altitude and
space monitoring. In the meantime, debate continued on the number of on-site
inspections necessary to ensure treaty compliance. The USSR, although
specifying no exact figure at this time, insisted the number should be
determined by political considerations, while the West held to inspections
automatically triggered by technical criteria. Due to Khrushchev's upcoming
visit to the US, as well as general elections in the UK, the negotiations
recessed in 1959 from August 26 to October 27.
Soon after the Conference resumed Tsarapkin proposed that a second working
group be convened to examine the controversial new seismic data introduced by
the US. The first presentation made in Technical Working Group II was by Carl
Romney, and concerned the HARDTACK II data. While including more details, he
basically concurred with the position presented in January, namely that the
magnitude of RAINIER had been overestimated and therefore many more earthquakes
of equivalent size existed. The Soviet response was couched in legalistic
terms, and again charged that no conclusions could be drawn regarding the
control system since the seismographs used in HARDTACK II were not identical to
those recommended by the Conference of Experts.
Although this charge in retrospect may seem irrelevant, other Soviet criticism
was more substantive. To begin with, fewer than thirty of the stations that had
recorded BLANCA and LOGAN were sufficiently calibrated to measure magnitude.
Data scatter was highly controversial as well. The Americans insisted that all
points should be used in computing an average, while the Soviets argued that
points in the so-called shadow zone, of intermediate distance, should be
excluded. The background to this argument concerns a property of the Earth of
great importance for seismic monitoring, associated with a layer of lower
seismic velocities hundreds of kilometers deep in the upper mantle, that has
the effect of defocusing seismic waves received in the horizontal distance
range about 1000 to 2000 km from an earthquake or an explosion. The property is
illustrated in Figure 1, which shows schematically the way in which the
amplitude of seismic waves at first decreases with distance, and later
increases, as the waves propagate to a range of distances from a shallow
earthquake or explosion. The region of low amplitude, or lack of observations,
is the shadow zone. At lesser distances (the First Zone), or greater distances
(the Third Zone), amplitudes are larger and are thus more likely to be
routinely observed above the noise. The inclusion of low amplitude signals
within the shadow zone tended to lower the seismic magnitude assigned to BLANCA
and LOGAN.
Figure 1. This shows the effect
of variation in seismic wave speed with depth in the Earth (see bottom right),
upon the path of propagation of the fastest seismic body waves (lower section,
showing ray paths of propagation in the crust and upper mantle). Amplitudes are
relatively strong, out to distance ranges of around 1000 km (the First Zone);
are weak or absent in the range around 1000-2000 km (the Shadow Zone); and
become strong again beyond 2000 km (the Third Zone). For the decades following
the 1963 signing of the LTBT, when nuclear testing was carried out underground
but no in-country verification was permitted, monitoring was conducted by
National Technical Means using seismic signals acquired typically in the Third
Zone. Nomenclature changed, such signals came to be called teleseismic
waves, and they have been intensively
studied especially for purposes of yield estimation in the context of the
Threshold Test Ban Treaty. With renewed attention to CTBT verification, and the
use of in-country stations, it has become more important to return to the study
of the strongest signals, acquired in the First Zone. Here too the name
changed, and such signals are more commonly now referred to as regional
waves. From [12].
The most dramatic moment in TWG II occurred when Hans Bethe and Albert Latter
officially presented the theory of cavity decoupling. Bethe later commented
[20] that the Russians seemed stunned by the theory of the big hole, a concept
that implied we considered the Russians capable of cheating on ... a massive
scale. After several meetings the Soviets admitted that Latter's work was
theoretically valid but argued there was no proof it could be made to work in
practice. The British delegation presented the results of several small tests
of TNT in cavities, conducted during the summer, which seemed to support the
theory. The participants were unable to devise any recommendations at this time
for foiling the decoupling strategy.
The final item covered in TWG II was the formulation of criteria to initiate
on-site inspections. The Soviets proposed that if the epicenter of an event
were located in an area of dense population, or if its focal depth were beyond
current drilling feasibility, it would be ruled an earthquake. Only events
exhibiting positive explosion characteristics should be considered for on-site
inspections. The Western delegates, stating that no such positive criteria
existed, introduced counterproposals that, according to the Soviet side, would
have made the majority of recorded events open to suspicion and eligible for
on-site inspection. An American proposal listed several potential methods that
might, after sufficient research, evolve into criteria for establishing an
event as an earthquake.
In the end, technical differences were too deep to allow TWG II to issue a
joint statement. The participants agreed instead on a report detailing the
proceedings, with four attached annexes. The first listed some generally agreed
recommendations on improvements, while the other three consisted of the
differing views of the Soviet, British, and American delegations.
On February 11, 1960, the US presented a new position at Geneva, proposing a
phased treaty that would immediately prohibit tests in the atmosphere,
underwater, and underground down to the lowest adequately controlled threshold.
This threshold was proposed to be 4.75 on a unified magnitude scale. According
to magnitude-yield data from Nevada (see above), the authors of the proposal
felt that this limit would correspond to about 19 or 20 kilotons, fully coupled
(i.e., tamped in the surrounding medium so that seismic waves would be excited
efficiently). In addition, the proposal accepted the idea of a numerical quota
of on-site inspections, probably 30% of unidentified events, which the authors
felt would be sufficient to deter cheating. On average this was believed to
correspond to twenty inspections in the USSR per year, and an equal number in
the US and UK together [4, p. 16]. The proposal concluded with a suggestion
that the three nations undertake joint seismic research to reduce the threshold
further.
The problem of proliferation, often cited as a strong reason for concluding a
test ban, resurfaced two days after this proposal. On February 13, 1960, France
exploded its first nuclear device, which was of 60 to 70 kiloton yield, in
Algeria, thereby ignoring recommendations of the UN General Assembly.
The USSR replied to the new US position on February 16. Tsarapkin at first
rejected the phased treaty concept since the USSR favored a comprehensive ban.
He proposed several temporary identification criteria, which might apply for an
initial period of two to three years. An event could be inspected if data from
several surrounding stations localized it to an area of 200 square kilometers,
but would be ineligible if its depth of focus were found to be more than 60
kilometers, its epicenter were found to be oceanic with no accompanying
hydroacoustic waves, or if it were established within 48 hours as the foreshock
or aftershock of an earthquake. However, on March 19, Tsarapkin issued a more
detailed proposal, in which the USSR announced a willingness to conclude a
treaty on the cessation of all nuclear weapon tests in the atmosphere, in the
oceans, and in outer space, and of all underground tests that produce seismic
signals of magnitude 4.75 or above [21]. He agreed to a joint research program.
While accepting most elements of the US proposal, the Soviet plan contained no
on-site inspection quota, and insisted on a moratorium on tests below magnitude
4.75.
In light of later seismic data and later negotiation of the Threshold Test Ban
Treaty, the acceptance by the USSR of a magnitude threshold is noteworthy. In
1960, magnitude 4.75 was regarded by US experts as corresponding to about 20 kt
for an underground explosion in Nevada under conditions of the RAINIER
explosion, though later the yield equivalence was found to be about 10 kt
(discussion of Romney testimony; see above). And, as also noted above,
magnitude 4.75 turned out to correspond to only about 2.5 kt at the principal
site the Soviets later developed for underground testing in East Kazakhstan. In
retrospect, a threshold test ban based on magnitude would therefore have
restricted yields on the East Kazakhstan Test Site significantly more than
yields at the Nevada Test Site. Some early hints at the conclusion that
magnitude-yield relations might vary between test sites were in fact available
in 1960, for although the USSR had not yet conducted an underground nuclear
explosion, the Soviets had experience with large underground chemical
explosions. For example, on March 3, 1960, 660 tons of TNT were placed in an
underground chamber and fired as a single charge at depth in Kirgizia
(present-day Kyrgyzstan), resulting in seismic waves so strong that they were
reported to the US as the equivalent of 5 kt fired under RAINIER conditions.
Today we would expect such a chemical explosion in Kirgizia, and a 5 kt
RAINIER-type nuclear explosion in Nevada, both to have magnitude around 4.5.
But in 1960 Albert Latter stated that "I personally do not accept the
Russian statement because they have not given any confirmatory details
[22]."
Several US research programs relating to underground verification were carried
out in 1960. Project COWBOY, conducted in March, consisted of a series of
chemical explosions set off in cavities, and generally supported the Latter
brothers' decoupling hypothesis, although indicating a decoupling factor lower
than 300. Accompanying studies concluded that the technology to construct such
cavities, through solution mining in salt domes, already existed. Project VELA,
the research effort in seismology recommended by the Berkner Panel, began in
1959 under the Advanced Research Projects Agency of the US Department of
Defense (DOD), and by 1960 had developed detailed plans for evaluating
detection and identification capabilities using small chemical and nuclear
explosions. The USSR protested that adequate safeguards must exist to prevent
these small nuclear shots from being used for weapon development purposes — and
indeed the US DOD had plans to couple such supposedly seismic experiments with
installations to study weapons effects [23]. But although the chemical explosions
under VELA were carried out, the nuclear explosions were postponed indefinitely
due to a lack of agreement on safeguards [4, p. 265].
Project VELA also included a plan by the US Coast and Geodetic Survey to build
a World-Wide Standard Seismograph Network (WWSSN), following the recommendation
of the Berkner Panel. The network would shortly grow to include about 125
stations, most outside the US, each recording in a standard analog format on
photographic paper. The stations recorded continuously, and this network
collected earthquake data around the world as well as nuclear explosion data.
The WWSSN had a profound influence on the growth and achievements of the
science of seismology, providing important support and insight into the theory
of global tectonics, which revolutionized the Earth Sciences in the 1960s. In
addition to the WWSSN, a decision was made to build seven small arrays in the
US that conformed to recommendations made in the Conference of Experts, and
designed explicitly to detect Soviet tests. The first of these, at Fort Sill,
Oklahoma, appeared capable of detecting events down to magnitude 4, equivalent
to a one kiloton shot, at distances over 2000 miles, (i.e. in the Third Zone)
although at the time it appeared identification would not be reliable until the
event approached the equivalent of 5 kilotons [24].
Meanwhile, the Geneva Conference turned to the question of how many control
posts would be needed and where they should be situated. On May 12, 1960, the
US proposed that in the initial phase of a three phase process, 21 posts should
be constructed in the USSR, 11 in the US, 1 in the UK, 2 on ships, and 12 on
islands in the Northern Hemisphere, for a total of 47. (In Washington two days
earlier, Secretary of State Christian Herter had been horrified to learn of a
study sponsored by the Department of Defense which estimated it would take $1
to 5 billion to install the 21 control posts in the USSR. The plan turned out
to include the building of large airfields by the US in the USSR, and hiring
icebreakers to take in supplies. The estimate was found to be inflated and the
study declared invalid a few weeks later [23, pp. 323 & 348].) The USSR
complained in Geneva that this scheme did not provide any posts in the Southern
Hemisphere, where the Western powers often tested. The Soviets instead
advocated 15 posts in the USSR, 11 in the US, 1 in the UK, 7 in Australia, 20
on islands belonging to the UK and US, 2 in Canada and/or Mexico, 2 in Africa,
and 10 on ships, for a total of 68 posts. In addition, the Soviets insisted
that no on-site inspections take place during the first phase of installation,
which would probably take four years. The Western powers argued for dividing
this phase into two two-year periods, and beginning inspections at the end of
the first period. At the time of the US election in November 1960, when John
Kennedy defeated Vice-President Richard Nixon, these differences remained
unresolved.
Figure 2 here shows the locations of stations (arrays) in a global network with
170 stations of the type discussed in Geneva in 1960; and, for comparison, the
International Monitoring System's two seismographic networks eventually adopted
for the Comprehensive Nuclear-Test-Ban Treaty agreed to in 1996 — which also
has 170 stations. (The Figure also shows the infrasound, hydroacoustic, and
radionuclide monitoring networks of the IMS.) The IMS includes a network of 50 primary stations which send
their data continuously to an International Data Centre, and a network of 120
auxiliary stations which record continuously but which contribute their data to
the IDC only upon request for specific time intervals. With this style of
operation, the detection threshold of the IMS expressed in terms of seismic
magnitudes is determined only by the primary network. The auxiliary network
provides additional data, as appropriate for particular seismic events, to
enable an improved characterization of a detected event. It is becoming clear
through practical experience with the IMS networks (which have been partially
operational since 1995) that the primary network of 50 stations, when
completed, can be expected to have a significantly better detection capability,
than was anticipated in 1960 for the 170-station global Geneva system. Thus,
had the Geneva system ever been built, it would have far exceeded the
capability that it was expected to have.
Figure 2. This shows global
monitoring networks. Upper: a design for a seismographic network proposed in
1960 [19, p. 58] and based upon the Penney proposal of 1958. Each continental
post was to be an array of about ten stations. Lower: the five networks of the
International Monitoring System established by the Comprehensive Test Ban
Treaty of 1996, using four different technologies. The primary seismographic
network of the IMS (50 stations) provides detection, adequate for location,
down to about magnitude 3.25 in Eurasia and North America. The auxiliary seismographic network
(120 stations) enables good identification capability. For more information on monitoring
capability as of the years around 2000 to 2002, see reference 41.
Upon assuming office, President Kennedy undertook a thorough reorganization of
the US arms control apparatus. A new unit of the State Department, the
Disarmament Administration, was created; Arthur Dean replaced James Wadsworth
as chief representative to the Geneva Conference; and Glenn Seaborg, who was
more inclined to favor a test ban, replaced AEC Chairman John McCone.
The new US position, presented when the Geneva Conference resumed on March 21,
1961, contained a few minor concessions. The US would now seek legislation
permitting the Soviets to examine the internal mechanisms of nuclear devices
employed in US seismic research and peaceful explosions programs [25, p. 56].
The US proposal continued to insist on a quota of twenty inspections per year
in the USSR, as opposed to the Soviet proposal for three, but was willing to
assign quotas of twenty inspections to the US and UK as well. Very few
modifications were made in the technical issues, however, and the US still
envisioned a threshold set at seismic magnitude 4.75.
The Soviet reply was pointed and negative. Tsarapkin denounced the testing of
weapons by France as a serious obstacle to progress, and accused the US of
dragging negotiations out long enough to shift research work for NATO into
French hands.
On August 28, 1961, virtually as a desperation measure, Ambassador Dean offered
to eliminate the 4.75 seismic magnitude threshold if the USSR would agree to an
increase in the number of control posts or on-site inspections. As expected,
the USSR rejected this proposal. Three days later the Soviet Union ended its
moratorium and conducted the first test of what would be its most extensive
series ever — a series that had obviously been in preparation for some time.
The accompanying statement minimized the importance of a test ban alone, and
used the French tests and current Berlin Crisis as pretexts for resuming
testing. The US Atomic Energy Commission reported that atmospheric nuclear
explosions in the kiloton range took place at the Semipalatinsk Test Site, in
East Kazakhstan, on September 1, 4, 5, 13, 17, and October 12, 1961; and east
of Stalingrad on September 6. On October 11, 1961, the Soviet Union's first underground
nuclear explosion took place, also on the Semipalatinsk Test Site. It had
magnitude about 4.8 [26]. This explosion was detected at six stations of the
USCGS's new worldwide network and at one Swedish station, and was apparently
identified as underground and nuclear [27], although the event was not widely
listed as the USSR's first underground nuclear explosion until the 1980s.
The US was ill-prepared to resume testing — Los Alamos and Livermore had not
even been allowed to buy cable since this might have signaled an intention to
break out of the moratorium [28] — but began with a small underground test on
September 15 while still refraining from atmospheric tests. The Soviet Union,
despite a UN resolution calling on it to refrain from a proposed atmospheric
test of 50 megatons or more, exploded the largest atomic device ever tested on
October 30. Its yield was estimated at 58 megatons, but Hans Bethe speculated
that if its fusion material had been encased in uranium rather than lead the
yield could have been in excess of 100 megatons [29].
Following a recess in the Geneva Conference during October and November, the
Soviet Union introduced a proposal for the immediate conclusion of a treaty
banning space, atmospheric, and underwater tests, and a moratorium on
underground tests pending an agreement on a control system. The US and UK
rejected any proposal omitting a specific control system and, in the absence of
any further progress, the Conference finally ended on January 29, 1962, without
the release of any joint communiqu_(c).
The collapse of the Geneva Conference coincided with the creation of a panel,
headed by Hans Bethe, to evaluate the most recent Soviet test series. This
panel stated that the USSR had made sizable gains in reducing the weight to
yield ratio of its weapons, in increasing overall yield, and in reducing the
size of the necessary fission trigger. The panel also concluded that much of
the preliminary research for this series was conducted during the three-year
moratorium on nuclear tests.
In the meantime, new seismic data became available regarding explosions in
various media. On December 10, 1961, Project GNOME, the explosion of a 3 kt
nuclear device in a salt dome in New Mexico, was conducted. Based on results
obtained in Project COWBOY, it had been believed that a fully tamped shot in
salt would produce a signal smaller, by a factor of perhaps two and one half,
than a tamped explosion in tuff, the rock type in which all previous US
underground tests had been conducted. Contrary to these expectations the
signals from GNOME were significantly larger than those of LOGAN, a 5 kt shot
tamped in tuff at the Nevada Test Site in 1958 [4, pp. 351-352]. The GNOME shot
was detected as far away as Japan and Sweden. This was the first clear indication
to the US that the relation between magnitude and yield could vary
significantly from one region to another. The reasons have to do with the
differences in rock type in the immediate vicinity of the shot point (which
affect the efficiency with which explosion energy is coupled into the energy of
seismic waves), and the differences in propagation characteristics of seismic
body waves in different geological regions (which affect the way in which body
waves are attenuated, as they travel from the seismic source to stations at
which the signal strength is recorded).
However, although the fact of the stronger-than-expected GNOME signals was
encouraging to those seeking effective ways to monitor underground nuclear
explosions, other results from this shot were less encouraging. The discovery
was made that seismic wave velocities through the Earth's crust were not
uniform from one region to another, making more difficult the analysis of
signals to obtain a source location. Had the USSR's proposed position on
inspection criteria been in force, a 200 square km area around the estimated
epicenter, the GNOME shot would have occurred outside the area eligible for
inspection. Furthermore, the depth of the GNOME event was not estimated near
350 meters, the actual depth of detonation, but rather at about 130 km, which
would have identified it as an earthquake. In general, these uncertainties led
many to lose confidence in the capability of seismological methods to verify a
nuclear test ban effectively. By making appropriate corrections for the
non-uniformity of the Earth's crust, event location could still be done
accurately. But what would be the confidence in the corrections, for an event
in an area where the corrections had never before been derived, and the ground truth
data to do so were unavailable?
On February 2, 1962, the US Atomic Energy Commission announced that earlier
that day the USSR had apparently conducted an underground nuclear test. The
test, widely reported to be the first underground Soviet nuclear explosion, was
carried out in a generally aseismic area in Soviet Central Asia (East
Kazakhstan), and had a yield estimated at 40 to 50 kilotons. The rapid
detection and rapid identification of this test were applauded by proponents of
the test ban [4, p. 353], few (if any) of whom knew that there were data,
available in the West, to indicate that a previous underground nuclear test at
the same test site had taken place in the USSR (see above).
The section of Project VELA concerned with cavity decoupling, Project DRIBBLE,
was planned to consist of six explosions, both tamped and decoupled. Due to
lack of funds this project was temporarily suspended after exploratory drilling
and engineering work. Upon its resumption in September 1962 a cavity for a 100
ton shot was planned which would require a year of work and cost $3.2 million.
By 1965 more than this had been spent and construction of the cavity had not
yet commenced — an indication, presumably, of the difficulty in executing a
decoupled explosion, even without the additional problems of keeping the shot
secret [30, p. 312].
Within two months of the end of the Geneva Conference, international pressure,
especially an emotional appeal from Prime Minister Harold Macmillan, led the
parties back to the negotiating table. The forum was now multi-lateral, and was
called the Eighteen Nation Disarmament Committee, consisting of five NATO
states, five from the Warsaw Pact, and eight non-aligned states. The ENDC, a
forerunner of today's Conference on Disarmament, convened on March 11, 1962,
and began with the Soviet Union tabling a draft treaty on General and Complete
Disarmament. The Soviets attributed the failure of previous negotiations solely
to US intransigence, and went on to claim that National Technical Means —
surveillance that a country could unilaterally achieve without cooperation from
the country being monitored — would be sufficient to detect underground as well
as atmospheric tests.
The US response consisted of a test ban proposal incorporating four modifications
to previous Western demands. First, to prevent surprise abrogation of the
treaty, heads of state would make periodic declarations that no test
preparations were underway, and declared test sites could be inspected by the
other party a certain number of times per year. Second, the inspection process
and the establishment of control posts were to be inaugurated sooner than the
two years previously discussed. Third, the 4.75 magnitude threshold was to be
eliminated due to the difficulty of determination, making the treaty
comprehensive. Fourth, on-site inspections would mainly be confined to a
normally aseismic area in Siberia, with only a few in the heart of the USSR.
Although the last two provisions were considered by the US to be major
concessions on its part, the USSR rejected this proposal, arguing again that
National Technical Means must suffice for any treaty.
Despite appeals from the non-aligned states as well as several allies, the US
resumed atmospheric testing on April 26, 1962. This series, which included a
few proof tests of existing stockpiles as well as new weapon development,
totaled about twenty megatons yield. Totaling the activities of the US, USSR,
UK, and France, more nuclear weapons were tested in 1962 than in any other
year, and more total megatonnage detonated, from September 1961 to December
1962, than in any other period of comparable duration.
While the ENDC was stalemated, several developments in the US increased support
for an atmospheric test ban. During the spring of 1962, following large test
series by the US and the USSR, the level of fallout-induced radioactivity was
found to have increased significantly worldwide. Several scientists proposed
that the concentration of iodine-131 in the atmosphere had reached dangerous limits,
and that protective measures might be necessary for some foodstuffs, especially
milk, if tests continued at the same rate. At the same time, US nuclear
strategy was officially stated to be changing from one of massive retaliation
to a doctrine of targeting Soviet weapons systems. Very large warheads thus
became less desirable, reducing the need for atmospheric tests.
During this period, Project VELA began to produce useful and specific results
leading to a more informed understanding of monitoring capability. An
underground French test, conducted in Algeria on May 1, 1962, was detected by
several of the new Coast and Geodetic Survey stations, and estimated at 30 to
50 kt. This test, like the Soviet tests in East Kazakhstan, indicated the
feasibility of teleseismic detection (i.e., data that had been acquired in what
earlier was called the Third Zone, beyond the shadow zone, see Figure 1, and
thus available by National Technical Means). Next, the discovery was made that
previous estimates of the annual number of shallow earthquakes in the USSR were
too large. These estimates, based on extrapolations of earthquake records from
1932 and 1936, had indicated 100 shallow earthquakes above magnitude 4.75 (then
thought to be equivalent to 19 or 20 kt in tuff), and 600 above magnitude 4.0
(then thought to be 2 kt in tuff). Using more recent and better data the
figures were revised to about 40 shallow earthquakes above magnitude 4.75, and
170 above magnitude 4.0 [31].
The placement of seismometers in deep boreholes was soon found to increase
signal to noise ratios by a factor of five or ten. In addition, special
filtering of data from surface arrays of many seismometers was seen to improve
capabilities considerably. Finally, research showed that seismometers positioned
on the ocean floor could provide useful monitoring data.
Some other developments, however, indicated new difficulties in detection.
Seismic signals measured in different directions from an explosion were found
to be of significantly different strengths. American scientists also discovered
that a test carried out in loosely compacted alluvium would produce a signal
only one-seventh as large as a test in tuff (and one-fourteenth as large as one
in granite). However, an underground test in alluvium would most likely cause a
cavity visible on the surface.
Overall, the Project VELA results were encouraging, and the US felt confident
enough to introduce two new draft treaties in Geneva on August 27, 1962. In the
eyes of the world, the US position was enhanced by the commencement of a new
Soviet test series on August 5, which included a 30-megaton shot. The first
draft for a Comprehensive Test Ban Treaty envisioned a fifteen member
International Scientific Commission (four Western, four Eastern, seven non-aligned)
to establish standards for the calibration and operation of all elements of the
verification system. This system would consist of nationally owned and manned
stations as well as several new facilities financed and staffed by the
Commission, to be constructed at sites listed in an annex to the treaty. Equal
quotas of on-site inspections would be assigned to the territory of the USSR,
UK, and US. Any event not positively identified as an earthquake, by first
motion or depth, would be eligible. No number was specified at this time for
inspections, but the UK and US delegates stated it would be less than the 12 to
20 previously proposed. Data from Project VELA now indicated that only about 10
to 15 unidentified events of magnitude ≥ 4.75 would occur in the USSR each year
[32, p. 15].
The second Western draft was a far briefer proposal for a Partial Test Ban.
This treaty prohibited tests in or above the atmosphere, in the seas, and in
any other environment if the explosion caused radioactive debris to escape
outside the territorial limits of the testing state. The last provision was
intended to prevent a nation from putting a small amount of earth over a
surface shot and styling it an underground test. The draft did not mention the
creation of a control system or international organization, nor did it call for
any moratorium on underground tests. Ambassador Dean, when presenting the
Partial Ban draft, declared it could and should be accepted immediately as a
means of limiting the arms race and stopping radioactive pollution.
Assistant Secretary of Defense Paul Nitze headed a panel to evaluate detection
capabilities under both proposed treaties. The panel estimated that the system
envisioned in the comprehensive draft could detect underground shots down to about
10 to 20 kt in alluvium, and 1.5 to 3 kt in tuff. Nitze stated that this
threshold would still allow the USSR to study most important technical
principles of nuclear weapons development, including those relating to neutron
weapons. His panel concluded that detection capability for atmospheric and
underwater tests was adequate, but that tests conducted in inland waters or
outer space would be difficult to detect [33].
The USSR rejected both treaties, the first because it still allowed for on-site
inspections that the West could use for espionage purposes, and the second
because it permitted underground tests. The eight neutral states in the ENDC
sought to placate the Soviets by proposing that the entire International
Scientific Commission decide which suspicious events should be inspected,
rather than the opposing nuclear power. The Western powers rejected this
suggestion and the ENDC recessed on September 7.
In October 1962, the crisis over Soviet missiles in Cuba convinced both
superpowers of the need for rapprochement. Having confronted the very real
possibility of nuclear war, the USSR and the US were more willing to moderate
negotiating positions. The Soviet Union indicated it would be willing to
consider the use of sealed automatic recording stations, nicknamed black boxes,
for in-country verification, based on a suggestion by three American and three
Soviet scientists at the Tenth Pugwash Conference in London. Ambassador Arthur
Dean revealed to the Soviets that the US might now accept 8 to 10 on-site
inspections per year, and 8 to 10 nationally manned control posts, in the
territory of the USSR.
When the ENDC reconvened in November, the USSR proposed the use of automatic
seismographic recording stations to eliminate the need for internationally supervised,
nationally manned stations as well as on-site inspections. Several weeks later
they suggested three possible sites for these black boxes, and announced they
would be willing to have international personnel participate in the
installation of these devices on Soviet territory. Although the Western powers
rejected the idea of eliminating on-site inspections, they proposed that a
group of experts be convened to discuss the black boxes.
Following this proposal Kennedy and Khrushchev exchanged letters discussing the
acceptable number of on-site inspections in the USSR. Kennedy advocated 8 to
10, while Khrushchev demanded 2 to 3. Private talks were then conducted in the
US between William Foster, director of the Arms Control and Disarmament Agency
(created in September 1961 in President Kennedy's new Administration), and
Soviet representatives. Potential black box sites in both countries were
proposed and accepted or rejected, and seismic noise-level data for the sites
exchanged. The US felt its requirements might be satisfied by as few as seven
such stations, but when the talks ended on January 31, 1963, the Soviets were
willing only to consent to three [25, p. 184]. The same day the talks ended,
Edward Teller presented a paper to a group of influential Republican
Congressmen, charging that acceptance of current Soviet proposals would be
equivalent to accepting an unpoliced moratorium.
Due to the unresolved inspection issue, opposition to a test ban developed in
the US — or at least to a CTBT. The Joint Committee on Atomic Energy conducted
hearings in March 1963, to discuss the technical aspects of verification. Carl
Romney testified that the seismographic system under consideration by the US
would be able to detect most tests down to 1 kt in granite, 2 to 6 kt in tuff,
and down to 20 kt in alluvium. However, he stated that decoupling could
attenuate seismic signals by a factor of 200 [30, p. 104]. Much of the
criticism of the Kennedy administration's determination to conclude a treaty
came from the Republican Conference Committee on Nuclear Testing, chaired by
Rep. Craig Hosmer, who had commanded the first occupation troops in Hiroshima
in 1945. It appeared that, even if an inspection number acceptable to the
Soviets were found, not enough support for a comprehensive ban existed in
Congress to provide the Senatorial advice and consent required to ratify a
Comprehensive Test Ban Treaty. Apparently Kennedy hoped to generate as much
support for the treaty in the Senate as possible, and wanted to receive more than
the minimum two-thirds vote needed for ratification. According to Glenn
Seaborg, then the Chairman of the AEC, Kennedy felt that the treaty needed to
be launched on a strongly positive note to serve its purpose as a first step to
a better world order [25, p. 258].
On July 2, Khrushchev announced that the USSR would be willing to accept a
treaty banning tests in the atmosphere, in space, and underwater. For the first
time, he did not insist that an underground moratorium accompany the treaty.
The following day US officials replied that the Administration would also
accept such a partial ban. President Kennedy dispatched the veteran diplomat W.
Averell Harriman to Moscow with broad instructions to attempt to conclude a
comprehensive ban, but to settle for a partial ban if necessary [25, p. 229].
After all the preliminaries, the final steps to conclusion of what has become
known as the Limited Test Ban Treaty were anticlimactic. The negotiations began
on July 15, 1963, with the US making a final attempt to negotiate a
comprehensive ban. An effort was made to arrange meetings between Frank Press,
the only seismologist in the US delegation, and Soviet seismologists, but it
was claimed that these were all away from Moscow or otherwise unavailable [4,
p. 455]. A few days later this attempt was abandoned, and a draft, based on the
Western proposal for a partial ban issued the previous year, was put forward.
A treaty, virtually identical to this draft, was composed, and signed on July
25 by Foreign Minister Andrei Gromyko for the USSR, Ambassador Harriman for the
US, and Science Minister Lord Hailsham for the UK. In five short articles, it
prohibited testing at sea, in the atmosphere, in space, and in other
environments if such tests caused radioactive debris to be present outside the
testing state's territory. The treaty was to be of unlimited duration, and
would be open to all states for signature. Signatory states would have the
right to withdraw with three months notice, if extraordinary events jeopardized
their supreme interests. Remarkably, no mention whatsoever was made of
verification systems or international control, it being assumed that National
Technical Means would suffice.
On August 5, the treaty was signed by Foreign Minister Gromyko (for the second
time), Secretary of State Rusk, and Foreign Secretary Lord Home. Three days
later it was submitted to the US Senate for advice and consent. Kennedy felt
that the endorsement of the Joint Chiefs of Staff, as well as a majority of the
scientific community, was essential to secure the consent of the Senate.
General Maxwell Taylor, Chairman of the Joint Chiefs of Staff, testified that
four crucial safeguards were necessary for the military to recommend
ratification of the treaty:
(1) An extensive underground test program must continue in order to improve the
US arsenal.
(2) Modern nuclear laboratory facilities and research programs must be
maintained.
(3) The resources and facilities to resume atmospheric tests promptly must be
maintained, in the event of Soviet non-compliance with the treaty.
(4) US capability to monitor the treaty and detect violations must be improved.
President Kennedy, in private conversations with the Chiefs, supported these
safeguards. In the view of Glenn Seaborg: "While this support may have
obtained the favorable testimony of the Joint Chiefs, it was at a very heavy
price for the cause of disarmament" [25, p. 271]. At the end of these
hearings, which lasted three weeks, the Joint Chiefs of Staff gave their
formal, if unenthusiastic, approval to the limited ban.
As expected, Edward Teller opposed the treaty, arguing that the US needed to
test in the atmosphere to learn more about weapons effects. Addressing the
Senate Foreign Relations Committee, he stated that if they consented to ratification,
"You will have given away the future safety of this country. You will have
increased the chances of war, and, therefore, no matter what the embarrassment
may be in rejecting the treaty, I earnestly urge you to do so and not to ratify
the treaty which is before you" [34]. John Foster, Director of the
Livermore Laboratories, considered the treaty disadvantageous from purely
technical-military considerations, and urged rejection. The Director of Los
Alamos, Norris Bradbury, supported the treaty, but only on condition that the
US government devoted itself to a vigorous underground test program. Hans Bethe
and other test ban proponents, while regretting failure to negotiate a
comprehensive ban, applauded the treaty as a useful first step [34, pp. 583
& 616].
Ratification of the Moscow Treaty, formally known as the Treaty Banning Nuclear
Weapon Tests in the Atmosphere, Outer Space, and Underwater, received the
consent of the US Senate, by a vote of 80 to 19, on September 29. The Presidium
of the Supreme Soviet voted unanimously to ratify the treaty on September 25.
On October 7 President Kennedy signed the Moscow Treaty, which entered into
effect on October 11. That same day, in Oslo, the Nobel Peace Prize was awarded
to Linus Pauling, one of the very earliest test ban advocates.
The Moscow Treaty, commonly referred to as the Limited Test Ban Treaty,
promptly found wide support. By the end of 1963, 113 nations had added their
signatures to those of the USSR, US, and UK, and by late 1994 over 145 states had
become signatories. The Peoples Republic of China, which was to test its first
atomic bomb in 1964, and France, which felt that its independent arsenal, the force
de frappe, still needed perfection through atmospheric tests,
were the most prominent states refusing to sign. However, although the LTBT was
successful as an environmental measure in that radioactive fallout was greatly
reduced (even France and China eventually stopped atmospheric testing — the
last such test being conducted by China in 1980), the treaty had little impact
on nuclear weapons development in view of the vigorous programs of underground
testing that continued for decades. The work to obtain agreements on a CTBT
verification regime (including provisions for in-country monitoring and on-site
inspection), though briefly considered again in the late 1970s, was effectively
postponed for a generation, beginning again on a multilateral basis at the
Conference of Disarmament in January 1994 in Geneva, where the work began so
many years before. The Conference on Disarmament produced a final CTBT text in
1996, which with one minor revision was adopted by the United Nations in
September 1996.
3. Further Comment on Key Technical Issues in Seismic Monitoring
The work of monitoring underground nuclear explosions using seismological
methods can usefully be broken down into the separate steps of signal
detection, location of the event, identification, and estimation of yield. All
these steps may be studied both for underground tests conducted non-evasively
(the practice under the LTBT); and for tests conducted evasively using various
methods (some, as yet hypothetical) to reduce or otherwise manipulate signals,
with the goal of avoiding detection and/or identification.
Improvements in signal detection came steadily throughout the early years of
Project VELA, along with improved methods of event location. The effectiveness
and engineering feasibility of the cavity decoupling method of treaty evasion
appears to be much more limited than envisioned in 1963. But the early
development of methods for event identification began with a setback, and a key
method that was indeed successful was discovered too late to have any impact in
the period 1958-1963.
The setback, was the early realization that the method of P-wave first motions was very unreliable, because it is
often impossible to be sure if the trace of a seismogram moves up or down at
the beginning of the arrival of P-waves
from either an earthquake or an explosion. (In practice, seismogram signals include
a background of noise, and it is common for P-waves to emerge as growing oscillations from this
background, with no clear indication of a first upward or first downward
movement.)
The key method of event identification that was successful was based upon use
of more than just the P-wave. To
explain this method, we must first note that earthquakes and underground
explosions produce several different seismic waves, falling broadly into three
types: those which travel through the body of the Earth (i.e. through its deep
interior); those which spread out over the surface of the Earth, analogous to
the way that ripples disperse over the surface of a pond; and those which are
guided along by the outer layer of the Earth (the crust). These three types of
waves are referred to as seismic body waves, seismic surface waves, and
regional waves. A subdivision of seismic body waves into so-called P-waves and S-waves
has been known since the 19th century. As noted above, P-waves travel faster than all other seismic waves,
and, though traveling in solid rock, are analogous to sound waves in air or
water. S-waves (the S standing for secundus) also travel through the Earth's deep interior, but
slower than P-waves. They consist of
a shearing motion in which particles move at right-angles to the direction the S-wave itself is traveling. The typical frequency of a P-wave or an S-wave, as recorded at teleseismic distances (see Figure 1, the Third
Zone), is in the range 0.5 – 5 Hz. Surface waves are also recorded
teleseismically, but with much lower frequency, typically around 0.05 Hz. The
strongest regional wave, known as the Lg-wave, may have frequencies in the range 0.3 – 3 Hz.
A number of seismologists noticed in the early 1960s that the different types
of seismic waves were excited to different levels by underground explosions,
than was the case with shallow earthquakes. Some of this work had in fact been
known for many years, but in the context of studying the signals from quarry
blasts, which are typically too small to detect except at regional distances.
Thus, a Harvard seismologist, Don Leet, who had specialized in the study of
quarry blasting, noted from teleseismic records of underground nuclear
explosions that they often lacked any S-wave signals even when the P-wave
was strong [35]. For earthquakes, the S-wave is usually much stronger than P. The use of what Leet called the “lonesome P” discriminant, however, was unreliable, for many
nuclear explosion records did in fact include S-wave signals and it was not until the 1990s that
careful quantitative work using regional waves turned this approach into a
useful method of event identification. More important, for purposes of
monitoring with teleseismic waves, was the discovery that underground nuclear
explosions are inefficient, relative to earthquakes, in exciting surface waves.
Much of the early work in this field was done at what was then called the
Lamont Geological Observatory of Columbia University in New York. For example,
James Brune and others in 1963 found from the study of more than a 100
earthquakes and 35 explosions that "Most of the earthquakes studied
generated surface waves 5 to 10 times greater than the maximum observed for
explosions when the explosions and earthquakes had short-period regional waves
of the same size" [36]. Liebermann and Pomeroy [37, 38] used traditional
methods of measuring the magnitude of teleseismic body waves (mb) and surface waves (Ms), and showed for an underground nuclear explosion in
the Aleutians that the Ms
value was only 3.9, whereas for an earthquake with the same mb as the explosion, the Ms value would be expected to be about 6.1. They then
applied this discrimination method to two seismic events in Southern Algeria
and successfully identified them as underground nuclear explosions, because the
surface waves from these events are much smaller than would be expected from
most earthquakes of comparable body-wave magnitudes.
The so-called Ms:mb discriminant was clearly successful for shallow
seismic events, if they were large enough to give teleseismic body-wave and
surface wave signals whose magnitude could be reliably measured. (For deep
events, other discriminants could be used.) The method resulted in many efforts
over a period of years to improve the ways that mb and Ms are measured, and many efforts to see if the
discriminant could be applied reliably at lower magnitudes. Figure 3 shows key
results obtained in 1971 (though not released until several years later) for
underground nuclear explosions at the Nevada Test Site and earthquakes in
Nevada, namely: that the method appeared to be reliable down to below mb 4; and that the two populations (of explosions and
earthquakes) did not appear to merge at low magnitude, so the method could
potentially be made to work at even lower magnitudes if signals could be
obtained (in particular, surface wave signals from small explosions) [39].
With the growth of the WWSSN in the early 1960s, signal quality was adequate to
apply the Ms:mb discriminant routinely on a global basis down to mb 4.5. For example, Sykes and others showed that for
events with mb ≥ 4.5,
90% could be identified as earthquakes based upon their depth being greater
than 30 km and/or their location being more than 25 km at sea; and all the
remaining 10% could be identified using the Ms:mb method [40]. This capability would appear to have been adequate to
monitor compliance with a trilateral underground test ban of the type
considered in the early 1960s, with a ban on events of magnitude 4.75 and
above, although the WWSSN stations would have needed augmentation to improve
detections in Eurasia.
Figure 3. A robust discriminant,
the plot of Ms against
mb, is shown for
earthquakes and underground nuclear explosions. Since magnitude scales are
logarithmic, the separation of the two lines by 0.8 magnitude units implies
that surface waves from earthquakes are, on average, more than 6 times larger
than surface waves from explosions having the same body wave magnitude. From
[39].
4. Conclusions
The capability to monitor a CTBT by
seismological methods was developed on an accelerated basis in the early 1960s,
but was then deemed inadequate, leading apparently to the need for significant numbers
of on-site inspections of suspicious events. In retrospect, we find that
monitoring methods turned out to be significantly better than they were
typically characterized at the time by key advisors. Presentations to the US
Congress, by witnesses characterizing the US monitoring effort, often gave
estimates of monitoring capability that later turned out to be significantly in
error, actual capability being better than the estimate. Great improvements in
capability were developed in the practical context of monitoring underground
nuclear weapons tests following the conclusion of the LTBT — not in the context
of earlier arms control negotiations.
The Geneva system of 170 control posts (see Figure 2) was never built, but, on
the basis of comparison with other networks, it appears it would have enabled
monitoring to be accomplished on a global basis down to mb 3 rather than mb 4, about a tenfold improvement over what was stated
at the time to be the desired monitoring capability.
5. Acknowledgements
Support to Richards’ research for
over three decades is acknowledged from the Advanced Research Projects Agency,
the Air Force Phillips Laboratory, the Air Force Office of Scientific Research,
the Defense Threat Reduction Agency and the Department of Energy. Note: the
views and conclusions here are those of the authors and should not be
interpreted as representing the official policies, either expressed or implied,
of the U.S. Government.
6. References
1. Kerr, D.M. (1988) in J. Goldblat and D. Cox (eds.), Nuclear
Weapons Tests: Prohibition or Limitation?,
Oxford University Press, New York, p. 43.
2. Magraw, K. (1988) Teller and the Clean Bomb Episode, Bulletin
of the Atomic Scientists, May issue, p. 32.
3. Gilpin, R. (1962)
American Scientists and Nuclear Weapons Policy,
Princeton University Press, Princeton, NJ.
4. Jacobson, H.K., and E. Stein (1966) Diplomats,
Scientists, and Politicians: The United States and the Nuclear Test Ban
Negotiations, Univ. of Michigan Press.
5. Johnson, G.W. (1985) Underground Nuclear Weapons Testing
and Seismology - a Cooperative Effort, in The VELA Program: A
Twenty-Five Year Review of Basic Research,
Defense Advanced Research Projects Agency, p. 10.
6. The New York Times (1958), April 3, p. 1.
7. Conference of Experts to Study the Methods of Detecting
Violations of a Possible Agreement on the Suspension of Nuclear Tests (1958)
Verbatim Records.
8. Teller, E. (1958), Alternatives for Security, Foreign Affairs 36, p. 204.
9. Murray, T. (1959) East and West Face the Atom, The New Leader, June 15, pp. 10-14.
10. US Congress (1959) Senate Committee on Foreign Relations, Subcommittee on
Disarmament, Hearings: Geneva Test Ban Negotiations, 86th Congress, 1st
Session, p. 29.
11. Ringdal, F. (1985) Study of magnitudes, seismicity and earthquake
detectability using a global network, in The VELA Program: A
Twenty-Five Year Review of Basic Research,
Defense Advanced Research Projects Agency, p. 611.
12. Romney, C. (1960) Detection of Underground Explosions, in Project
Vela, Proceedings of a Symposium, October,
pp. 39-75.
13. Murphy, J. (1981) P-wave coupling of underground explosions in various
geologic media, in E.S. Husebye and S. Mykkeltveit (eds.), Identification
of Seismic Sources Earthquake or Explosion,
D. Reidel, Dordrecht, pp. 201-205.
14. Ringdal, F., P.D. Marshall and R. Alewine (1992) Seismic yield
determination of Soviet underground nuclear explosions at the Shagan River test
site, Geophysical Journal International 109, 65-77.
15. US Department of Defense (1959) Press Release, Jan 16.
16. Latter, A., R. LeLevier, E. Martinelli, W. McMillan (1959) A Method of
Concealing Underground Nuclear Explosions, RAND Corporation, Mar. 30.
Subsequently published (1961) Journal of Geophysical Research 66, 943-946.
17. Street, K. (1959) Need for High Explosive and Nuclear Tests for Research
Program, Report of the Berkner Panel, p.
54.
18. Report of the Berkner Panel (1959), p. 15.
19. Project Vela, Proceedings of a Symposium (1960), October.
20. Bethe, H. (1960) The Case for Ending Atomic Testing, The Atlantic
Monthly 206, p. 48.
21. Conference on the Discontinuance of Nuclear Weapon Tests, Geneva (1958-62)
Verbatim Records, section 188, p. 13.
22. Latter, A. (1960) Decoupling of underground explosions, in Project Vela,
Proceedings of a Symposium, October, p.
180.
23. Kistiakowsky, G.B. (1976) A Scientist at the White House, Harvard University Press, Cambridge.
24. Romney, C. (1962) US Congress, Joint Committee on Atomic Energy, Hearings:
Developments in the Field of Detection and Identification of Nuclear Explosions
(Project Vela) and their Relationship to Test Ban Negotiations, 87th Congress,
1st Session, pp. 123-4.
25. Seaborg, G.T. (1981) Kennedy Khrushchev and the Test Ban, Univ. of California Press, Berkeley.
26. Khalturin, V., T. Rautian, and P.G. Richards (2000), A study of small
explosions and earthquakes during 1961-1989 near the Semipalatinsk test site,
Kazakhstan, accepted for publication, Pure and Applied Geophysics, 2000.
27. Båth, M. (1962) Seismic records of explosions - especially nuclear
explosions: Part III, Forsvarets Forskningsanstalt (Swedish Defense Research
Establishment), FOA report 4, A 4270-4721, December, pp. 60-63.
28. Agnew, H. (1987) personal communication to one of the authors (PGR).
29. Bethe, H. (1962) Disarmament and Strategy, Bulletin of the Atomic
Scientists 18, 14-22.
30. US Congress (1963) Joint Committee on Atomic Energy, Hearings: Developments
in Technical Capabilities for Detecting and Identifying Nuclear Weapons Tests,
88th Congress, 1st Session.
31. Foster, W. (1962) U.S. Congress, Disarmament Subcommittee Hearings: Renewed
Geneva Negotiations, 87th Congress, 2nd Session, 25 July.
32. US Congress (1963) Senate Committee on Foreign Relations, Hearings: Test
Ban Negotiations and Disarmament, 88th Congress, 1st Session, 1963.
33. US Congress (1962) Senate Armed Services Committee, Preparedness
Investigation Subcommittee, Hearings: Arms Control and Disarmament, 87th
Congress, 2nd Session, p. 13.
34. Teller, E. (1963) US Congress, Senate Committee on Foreign Relations,
Hearings: Nuclear Test Ban Treaty, 88th Congress, 1st Session, p. 428.
35. Leet, D. (1962) The detection of underground explosions, Scientific
American 206, 55-59.
36. Brune, J., A. Espinosa, and J. Oliver (1963) Relative excitation of surface
waves by earthquakes and underground explosions in the California-Nevada
region, Journal of Geophysical Research 68,
June 1, 3501-3513.
37. Liebermann, R.C., C.-Y. King, J.N. Brune, and P.W. Pomeroy (1966)
Excitation of surface waves by the underground nuclear explosion Longshot, Journal
of Geophysical Research 71,
4333-4339.
38. Liebermann, R.C., and P.W. Pomeroy (1967) Excitation of surface waves by
events in Southern Algeria, Science 156,
1098-1100.
39. Lambert, D.G., and S.S. Alexander (1971) Relationship of body and surface
wave magnitudes for small earthquakes and explosions, SDL Report 245, Teledyne
Geotech, Alexandria, Virginia.
40. Sykes, L.R., J.F. Evernden, and I. Cifuentes (1983) Seismic methods for
verifying nuclear test bans, in D.W. Hafemeister and D. Schroeer, Physics,
Technology and the Nuclear Arms Race, AIP
Conference Proceedings, no. 104, AIP, New York.
41. National Academy of Sciences report, Technical issues related to
the Comprehensive Nuclear Test Ban Treaty,
2002, available via http://www.nap.edu