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YIELDS OF UNDERGROUND NUCLEAR EXPLOSIONS ATAZGIR AND SHAGAN RIVER, USSR AND IMPLICATIONS FOR IDENTIFYINGDECOUPLED NUCLEAR TESTING IN SALT

Lynn R. Sykes

Columbia University in the City of New YorkBox 20, Low Memorial LibraryNew York, NY 10027

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I5 December 1991 Scientific No. 14. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Yields of Underground Nuclear Explosions at Azgir and PE 62101F

Shagan River, USSR, and Implications for Identifying PR 7600 TA 09 WU BK

Decoupled Nuclear Testing in Salt6. AUTHOR(S) Contract F19628-90-K-0059

Lynn R. Sykes

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13. ABSTRACT (Maximum 200 words)

Bodywave magnitudes, mb, are recomputed using station corrections for all known Soviet under-ground nuclear explosions at Shagan River and Azgir. The m b values for explosions of announcedyield, Y, in various parts of the world in either hard rock or below the water table were normalizedto the SW part of the Shagan River testing area using previously published values of t* and mb bias.The resulting relationship, mb = 4.48 + 0.79 logY, which includes yields published by Bocharovet al. (1989) for Shagan River, differs very little from a regression that does not include those data.Using magnitudes determined from Lg at NORSAR as a standard, the Shagan River site is dividedinto three subareas. Yields calculated from these revised m b values and from m(Lg) are muchmore consistent for the same explosion; each agrees closely with the yields published by Bocharovet al. for large explosions in 1971 and 1972 in the NE and SW parts of the testing area. Yields cal-culated by averaging determinations from Lg and body waves for 66 explosions have a high pre-cision at 95% confidence (mean value 1. 14) for Y > 10 kt. The explosion of 23 July1973 of Y =193 kt is clearly the largest underground explosion at Shagan River. The newly calculated valuesprovide strong evidence of clustering in the distribution of yields of Soviet tests. In a special study

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46yields of Soviet nuclear explosions, nuclear tests in salt, decoupling, evasion 1s. PRICE CODE

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made for the Azgir explosion of 1.1 kt of 1966, mb was measured at 16 stations for which seismo-grams were available, giving mb = 4.52 + .06. For purposes of appreciating the detection capabil-ity of a given seismic network, it is important to recognize that a fully-coupled explosion of I kt insalt in high-Q areas of the U.S.S.R. has an mb of 4.46; fully decoupled events of I and 10 kt havemb's of 2.61 and 3.40 respectively. Yields are recalculated for past Soviet nuclear explosions atAzgir and in other areas of thick salt deposits through 1986. The yields of fully decoupled andnearly fully decoupled (Sterling conditions) nuclear explosions that could be detonated in the cav-ities produced by those events are calculated. Most of the "opportunities" for decoupled testing ofthose types are concentrated in the area to the north of the Caspian Sea. The "oppontunities" forthe largest tests, up to a maximum of 7 to 8 kt, are largely confined to Azgir itself. Possibilities fordecoupled testing are more restricted in the area of bedded salt to the northwest of lake Baikal.

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CONTENTS

In tro d u ctio n 1................................................................................................................. 1Research A ccom plished ........................................................................................................... 5

Improved Bodywave Magnitudes ................................................................................. 5Sm all A zgir Explosions ................................................................................................... 6Magnitude-Yield Relationships for Shagan River and Azgir ................................. 6

Subdivision of Shagan River Testing Area for Yield Determination .................. 7Precision and Accuracy of Yield Determinations for Shagan River Explosions ...... 9Yields Determined from Surface Waves for Shagan River Explosions .............. 9Yields of Weapons Deployed on Soviet Strategic Delivery Systems

and Tested at Shagan River ....................................................................................... 11

Clustering of Yields of Shagan River Explosions ................................................... 12

Soviet Compliance with the Threshold Test Ban Treaty ....................................... 12

Cavities Formed by Nuclear Explosions in Thick Salt Deposits thatMight be Usable for Future Clandestine Nuclear Testing ................................. 13

Conclusions and Recommendations .................................................................................... 17Implications for Identifying Small Decoupled Nuclear Explosions in Salt ..... 17Precise Yield Estimates for Explosions at Shagan River ......................................... 17

R eferen ces .......................................................................................................................................... 19F ig u res ................................................................................................................................................ 2 1

T ab les .................................................................................................................................................. 27

DTIC TABUnan nounced 13

Justiticat __

DiStribut~onAvallabillty Codes

1iii

INTRODUCTION

The detonation of nuclear explosions by the Soviet Union in large underground cav-ities under either a Low-Yield threshold test ban treaty (LYTTBT) or a comprehensivetest ban treaty (CTBT) would constitute the greatest challenge to U.S. verificationefforts.That evasion scenario sets the limit on how low a yield can be verified effec-tively. The recent OTA Report Seismic Verification of Nuclear Testing Treaties foundthat between I to 2 and 10 kilotons (kt) the only plausible method of evasion is that ofnuclear testing in large cavities in salt domes. It concluded that no method of evadinga good monitoring network is credible above 10 kt and that several evasion scenarios,including testing in cavities in bedded salt and in hard rocks, are possible below 1 to 2kt.

Our work address a number of aspects of the problem of clandestine nuclear testingin large cavities in salt domes, bedded salt and hard rock--what types of evasion sce-narios are plausable based on geological and engineering constraints, which ones arelikely to escape detection by the U.S. and which ones are likely to be identified. Wedevote particular attention to the Soviet Union and to the critical yield regime from 1 to10 kt, where scientific research over the next few years seems most likely to have amajor impact on the verifiability of a LYTTBT and on what threshold can be verifiedeffectively. Several important aspects of decoupling have received little study formore than 20 years. Since then a great deal of experience has been obtained by theU.S. and several European countries on the rheological properties of salt in conjunctionwith research on radioactive waste disposal in salt deposits and by industry on the con-struction and stability of large cavities in salt for petroleum storage and waste disposal.Experience with very large cavities in salt domes is available from the U.S. StrategicPetroleum Reserve and from the U.S.S.R. and U.S. on cavities in salt for gas storage.

Our major research objectives during the first year were:1) Derive revised mb values for Soviet underground nuclear explosions in salt and

for small explosions at the main Soviet test sites; determine improved magnitude-yieldrelationships, especially for explosions of small yield;

2) Study numbers, magnitudes and spectral character of small earthquakes and largechemical explosions in and near areas of thick salt deposits in the U.S.S.R.;

3) Evaluate and synthesize data from engineering, rock mechanics and geologicalsources on the properties of salt, stability of large underground cavities in salt, and theuse of cavities in salt for possible clandestine nuclear testing, especially in the yieldrange I to 10 kt;

4) Start work on maps of the U.S.S.R. showing locations suitable for possible decou-pled testing of explosions of various yields in salt. Identify areas that have known salt

deposits, those that are not known to but conceivably could be such sites, and areas thatdo not and cannot contain salt deposits of any appreciable thickness (such as old cra-tonic regions and young volcanic areas).

During the past year work has been done on all four of the above areas. The firsttopic has been completed and a paper on that work is being finished for journal sub-mission. Most of this report is devoted to that topic and to the implications for detect-ing and identifying decoupled nuclear testing in the Soviet Union in the Azgir regionand in adjacent areas to the north of the Caspian Sea where the world's most numeroussalt domes are found.

There has been a long debate going back before the signing of the TTBT in 1974about the yields of Soviet underground nuclear explosions at their various test sites andabout the correct methodology for calculating explosion yield from the amplitudes ofvarious seismic waves. The establishment of a threshold in terms of yield by the TTBTput a premium on accurate yield determination. After 1974 the debate in the UnitedStates focused upon the Shagan River portion of the Soviet testing area in Central Asia(eastern Kazakhstan) since the largest underground nuclear tests by the U.S.S.R. afterthe start date for that treaty (April 1, 1976) were conducted there. (The Shagan Riverarea is called the Balapan testing area by Soviet workers.) Until three years ago whenBocharov et al. (1989) published yields of a number of underground explosions at theCentral Asian test site for the period 1961 through 1972, an approximate yield had onlybeen published or released by the Soviet Union for a single explosion in that area. Theuse of that data point for calibrating yields of fully contained underground nuclearexplosions was difficult since that event, which occurred in January 1965, produced alarge crater. Its mb was probably smaller than that of a fully contained explosion of thesame yield.

Underground nuclear explosions at the main Soviet test sites in Central Asia andNovaya Zemlya generate larger P waves at large (teleseismic) distances that U.S.explosions of the same yield at the Nevada Test Site (NTS). The difference in magni-tude, often called the mb bias, is + 0.3 to +0.4 magnitude units for either of those Sovietweapons testing sites with respect to NTS, providing the explosions are in the samerock type (Office of Technology Assessment, 1988). In practice, most U.S. under-ground explosions have been conducted in softer, less competent rocks than those atShagan River, leading to an overall bias of about 0.4 to 0.5 with respect to NTS.

In 1988 the United States and the U.S.S.R. conducted nuclear explosions at NTSand Shagan River, respectively, that were stipulated by bi-lateral agreement to be in theyield range from 100 to 150 kt. Each country permitted the other to make on-site mea-surements of yield by hydrodynamic (Corrtex-type) and seismic methods. It is unfor-tunate that yield estimates and other pertinent data for those two Joint VerificationExperiments (JVEs), as well as yield determinations for five previous nuclear tests at

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each site that were communicated to the other country, remain classified and have notbeen announced publically. Nevertheless, a detailed technical report on the two JVEsin the New York Times for October 30, 1988 stated that the American and Soviet on-site measurements by the hydrodynamic method gave yields of 115 and 122 kt, respec-tively for the Soviet JVE of September 14, 1988.

In previous work my colleagues and I determined yields for Soviet explosions atShagan River and Novaya Zemlya by using calibration curves for P waves that werebased on underground explosions of announced yield for which their P-wave magni-tudes were corrected for mb bias between the actual test site of the explosion and theSoviet site in question. Sykes and Ekstrom (1989) showed that the reported hydrody-namic yields of 115 and 122 kt for the Soviet JVE were consistent with those mb-yieldrelationships for Shagan River. They also obtained a maximum value of 145 kt for theyield of that explosion using surface waves.

In the last few years much progress has been made in using magnitudes derivedfrom the short-period seismic phase Lg for precise determinations of yield of explo-sions at Shagan River (Ringdahl and Fyen, 1988; Ringdahl, 1989; Ringdahl and Mar-shall, 1989; Hansen et al., 1990). The precision of a single determination of magnitudefrom Lg waves is often comparable to that obtained after averaging values of mb from50 to 100 worldwide stations. Magnitude: determined from Lg waves, m(Lg), willprobably become the single method of choice in the future as more data become avail-able from digitally-recording stations in the Soviet Union at regional distances. Lgwaves studied by Ringdahl and his co-workers were recorded digitally at Norsar andGraftenberg at distances of about 4000 km from Shagan River. Events of mb less thanabout 5.5 (Hansen et al., 1990), that is for yields smaller than about 40 kt, typicallyhave a small signal-to-noise ratio at those large distances. It appears possible to usedata from high-quality stations in the U.S.S.R. to determined yield from Lg waves fortamped (well-coupled) explosions as small as I kt (Hansen et al., 1990).

Nevertheless, accurate determinations of yield from mb continue to be essential formost past explosions of small to moderate yield at Shagan River and at other Soviettesting areas, explosions detonated in the 1960s before digital data of high qualitybecame available from either Norsar or Graftenberg, Peaceful Nuclear Explostions(PNEs) in areas of the U.S.S.R. more distant from those arrays, and explosions inregions like Azgir where the propagation of Lg is poor to many stations. Yields deter-mined from mb become a valuable check on calculations from Lg and can be used tomeasure the precision of yield determinations by the two methods. I show later that

more precise yields for Shagan River explosions can be obtained by suitably averagingdeterminations from mb and m(Lg) than can be obtained from either of those wavetypes alone.

A major problem exists in converting relative yields from Lg into absolute yields, i.

3

e. in calibrating a given test site in an absolute sense. While yields for several explo-sions at Shagan River prior to 1973 have recently been published by Soviet workers(Bocharov et al., 1989) and yields of five other Soviet explosions have been turnedover to the U. S. Government, the Soviet JVE of 1988 is the only event for which yieldhas been determined independently on-site by experts from outside the Soviet Union.As mentioned above, the yields measured on-site for the JVE and those five eventshave not been formally released or published by either the U. S. or Soviet govern-ments. Thus, calibration of absolute yields for Shagan River from Lg alone must bebased on either the single data point for the Soviet JVE or the unverified yieldsreported by Bocharov et al. (1989).

Body wave-yield relationships, however, have the advantage that data from manyexplosions of announced yield in other parts of the world can "transported" to theShagan River site via relative bias values for mb, such as those determined from atten-uation. This has the advantage of relying on more than a single Mb-yield pair of valuesin constructing a magnitude-yield relationship for explosions at Shagan River.Ringdahl and Marshall (1989) calibrated a mb-yield relationship for that site using themb value and approximate yield (111 kt) of the cratering explosion of January 15, 1965and then making a correction (addition) to its mb to account for its very shallow depthof burial, i. e. for the fact that, unlike almost other Shagan River explosions, it was notcontained. Since Lg measurement were not available for that event from Norsar orGraftenberg, Ringdahl and Marshall (1989) regressed data on m(Lg) with those on nibfor many contained explosions to obtain a m(Lg)-yield relationship and thence to com-puted yields of other events from that expression. Their absolute values of yield are, ofcourse, sensitive to the uncertainties in the values of mb, yield and the mb correctionterm for the 1965 event.

In this paper I compare my recalculated values of mb with values of m(Lg) reportedby Ringdahl and Fyen (1988) and Ringdahl (1989) for large numbers of explosions atShagan River. The difference betwcen those two magnitudes is shown to vary system-atically from southwest to northeast across that testing area. That variation is attrib-uted to systematic differences in mb (and hence in mb bias with respect to NTS), withLg being generated uniformly throughout the entire Shagan River area. Subdividingthe Shagan River area into three parts, corrections to mb are then made as a function oflocation on the test site to form a corrected body wave magnitude, mb' The values arenormalized to the southwestern part of the Shagan River area where mb = mb'.

I then use mb values for explosions of announced yield, Y, in various parts of theworld and correct them to the southwestern part of the Shagan River testing area usingthe bias values determined from the relative attenuation of P waves by Der et al. (1985)for various testing areas. A regression of mb upon log Y is obtained for those data butomitting the yields of Bocharov et al. (1989). Fortunately, the explosions with the

4

three largest yields in Bocharov et al. were located in the three different subareas of thetest site that I define. When their mb values are corrected for position on the testingarea, the corrected values, Mb', and their published yields fall very close to the mb-

yield relationship determined without recourse to those data points. This indicates thatthe Bocharov et al. yields must be nearly correct and that they are neither seriouslybiased nor unrepresentative. It also indicates that it is, in fact, mb and not m(Lg) thatvaries systematically with position on the test site. (Consistent yields are not obtainedif mb is taken to be constant and m(Lg) varies over the testing area).

Thus, to obtain yield estimates for Shagan River explosions from mb that are moreaccurate than a factor of 1.4 , it is necessary to use somewhat different mb-yield cali-bration curves for various parts of that test site. Values of m(Lg) are then regressedagainst mb' so that a new magnitude mt(Lg) can be calculated from Lg. In that waythe mb-yield relationship that was obtained for the southwest part of Shagan River(Fig. 1) can be used to obtain very accurate yield estimates of explosions at ShaganRiver from either mb', mb(Lg) or a weighted average of those two magnitudes. Anadvantage of this calibration procedure is that it does not rely on the magnitude or yieldof a single event like the Soviet JVE or the 1965 cratering explosion, it also permits theyields published by Bocharov et al. (1989) to be verified.

The yields obtained herein by an equal weighting of data from P and Lg wavesagree very closely, i. e. within about 15%, with those calculated by Ringdahl and Mar-shall (1989) using the 1965 cratering event for calibration. Seismology appears to beclearly capable of providing yields for large Shagan River explosions that are at leastas good as and often better than those attributed to the Corrtex method (Office of Tech-nology Assessment, 1988). For small explosions at that site, seismic methods have aclear advantage for yield determination compared to Corrtex (Office of TechnologyAssessment, 1988). For other less well calibrated test sites, like Novaya Zemlya, oneto a few Corrtex measurements can be used to calibrate the site such that seismicwaves can be used to estimate yields more accurately for past and possibly futureexplosions in that area.

RESEARCH ACCOMPLISHED

Improved Bodywave Magnitudes

Revised mb values were recomputed using station corrections for all known Sovietunderground nuclear explosions at the Shagan River testing area in Central Asia and inthe Azgir region to the north of the Caspian Sea for which data were available from theInternational Seismological Center (ISC) and the United States Geological Survey

5

(USGS) for the period January 1961 through May 1988. Station corrections forShagan River events were derived for 9 large explosions and applied to all undergroudevents for which data were available for that testing area. Similar previous work onmagnitude and yield determination are described in Sykes and Cifuentes (1984), Sykesand Ruggi (1986, 1989), Sykes and Davis (1987) and Sykes and Ekstrom (1989). Sta-tions used in the recalculations were confined to the distance range 250 to 950 .

A major object in our work has been to reduce the standard error of the mean for mbto values as small as 0.015 to 0.03 by using large numbers of stations (80 to 100 forlarger events) and by applying station corrections. Since individual stations typicallyrecord explosions from a given test site with amplitudes that are consistently eitherhigher or lower than the mean for many stations, the application of station correctionsconsiderably reduces the standard deviation of a single reading and avoids biasesrelated to the inclusion or exclusion of individual readings from one event to another.It is particularly important to use station corrections since data from the many stationsof countries like Canada or France were not available for some explosions but wereavailable for many others. Similarly, station corrections were derived for the sevenlargest underground explosions at Azgir, where the testing medium is salt, and appliedto other events at Azgir, including the PNE explosions of 1966 and 1968 for which theSoviet Union long ago announced yields of 1.1 and 25 kt respectively. Recomputedmagnitudes for Azgir and Shagan River explosions, their standard errors of the mean,and other pertinent data are listed in Tables I and 2.

Small Azgir Explosions

In a special study made for the Azgir explosion of 1. 1 kt of 1966, mb was measuredat 16 stations for which seismograms were openly available, giving mb = 4.524 + .056.Although small in amplitude, P waves could be readily identified at many of the betterWWSSN stations of higher gain and good signal-to-noise ratio. The ability to detectsuch a small event 25 years ago using analog records from mainly simple (non-array)stations reflects the high coupling of a tamped underground explosion in salt and theefficent propagation (high Q) for P waves from the Azgir area to stations worldwide Asimilar study for the 1968 Azgir PNE event gave mb = 5.529 + .027.

Magnitude-Yield Relationships for Shagan River and Azgir

The mb values for explosions of announced yield, Y, in various parts of the world ineither hard rock or below the water table were normalized to the southwestern part ofthe Shagan River testing area and to Azgir using the published values of relative atten-uation and mb bias of Der et al. (1985). For example, a bias of 0.351 mb units between

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the southwest part of the Shagan River testing area and NTS was used. Values of mh, inFig. I for Soviet explosions are from Tables I and 2; those for other events are fromMarshall et al. (1979).

An aim here has been to use as few Soviet announced yields as possible so as to per-mit the yields of Bocharov et al. (1989) and other yields recently turned over by theU.S.S.R to the U.S. to be verified. The resulting mb-yield regression (dotted line inFig. 1) for the southwest part of the Shagan River area,

mt = 4.483 + 0.787 logY (1)

which includes yields published by Bocharov et al. (1989) for Shagan River, in fact,differs very little from the other regression in Fig. I (solid line) that does not includethose data but does include the yields of PNE explosions at Azgir in 1966 (1.1 kt) and1968 (25 kt), which were made public many years ago as part of an exchange of dataon peaceful uses of nuclear explosions. The inclusion or exclusion of the two Azgirevents mainly affects the slope of the mb-log Y relation and not the computed magni-tudes for yields from 100 to 150 kt. A similar relationship,

mb = 4.456 + 0.787 logY (2)

was obtained for Azgir using a bias of 0.324 with respect to NTS (Der et al., 1985). Itcan be seen that the two explosions in salt at Azgir couple as well as those in hard rockat Shagan River as do the three in granite in Nevada.

Subdivision of Shagan River Testing Area for Yield Determination

Magnitudes determined from Lg at Norsar, m(Lg), and our recalculated values ofmb are now available for large numbers of events at Shagan River. Fig. 2 shows thatthe difference between m(Lg) and mb varies systematically across the Shagan testingarea from low values in the southwest to high values in the northeastern part, much likethat found previously by Ringdahl and Marshall (1989). In constructing Fig. 2 1 usedthe locations of Marshall et al. (1984) as well as Marshall, written communication, formore recent events. Using m(Lg) as a standard, the Shagan River test site is dividedinto three subareas. The straight line boundaries between the subareas were drawnsuch as to minimize the number of misfitting data points and to be approximately par-allel to structural features on and near the test site. A new magnitude mb' is definedequal to mb for the southwestern area, mb + 0.145 for the northeastern area, and mb +0.067 for the transitional zone between them. Much less scatter is evident for the sub-regions and for the entire Shagan River area (Figs. 3 and 4) when m(Lg) is comparedwith mb' rather than with mb.

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Yields for Shagan River Events from Lg and Bodywaves

A new magnitude,

mb(Lg) = 1.090 m(Lg) -0.440 (3)

is defined from the regression of mb' and m(Lg) that is shown in Fig. 4. This permitsyields for Shagan River events to be calculated from either m(Lg) or mb' using (1).This permits Lg observations to be used for yield determination using the much largercollection of mb values that are available for explosions of announced yield on aworldwide basis. Its use also avoids using mainly unverified Soviet yields when calcu-lating yield directly from observations of Lg. Yields calculated from those two magni-tudes are much more consistent for the same explosion than those calculated from Lgand uncorrected body wave magnitudes. The same is true for the yields of the threelargest explosions published by Bocharov et al. (1989)--125, 140 and 165 kt, which

occurred at Shagan River in 1969 and 1972 in each of the subregions defined in Fig. 2.The quantities mb', mb(Lg) and the average of those two magnitudes were each

regressed against logY using the published yields for those three explosions and theaverage yield, 119 kt, determined from hydrodynamic measurements for the SovietJVE as published in the New York Times (Sykes and Ekstrom, 1989). The slope ofeach magnitude-log Y relationship was held constant at 0.8 since the yields cover avery narrow range. Each of those magnitudes had the following standard deviations:ob', 0.046; mb(Lg), 0.035; average magnitude, 0.018 magnitude units. While aslightly better weighted average of the two computed values of log Y could be calcu-lated, only a simple average seemed warranted at this time. Nevertheless, it is clear forthese four events that the precision of yield estimates can be improved by using anaverage based on the magnitude determined from Lg and the corrected magnitude mb'rather than relying on yield estimates based on either of those magnitudes alone.

Close agreement is found between the yields published by Bocharov et al. (1989)

and those calculated from the relationship in Fig. 1 that does not include those data orany other recently released Soviet data. Thus, the published of yields Bocharov et al.for Shagan Ri,,er must be equal to or close to the actual yields. The inclusion of thefour yields of Bocharov et al. for Shagan River explosions, in fact, leads to slightlylarger computed yields than those obtained in Fig. I without those data. The yieldcomputations based on mb' in Table I utilize the relationship that includes those data.Nevertheless, they do not differ significantly from those computed with the other rela-tionship in Fig. 1. The close agreement between yields computed from mb' andmb(Lg) and those published by Bocharov et al. also argues that mb , in fact, and not

8

m(Lg) varies with position from southwest to northeast across the Shagan River testing

area.

Precision and Accuracy of Yield Determinations for Shagan River Explosions

The values of log Y obtained by taking a simple average of the magnitudes obtainedfrom Lg and bodywaves for 66 Shagan River explosions of Y > 10 kt (Table 1) havestandard errors of the mean (SEM) between 0.00 and 0.08 and an average SEM of .029.These translate into yield determinations based on those two wave types with a preci-sion at 95% confidence (R value) of a factor of 1.0 to 1.45 (mean value of 1.14) (Fig. 5).Only one explosion of yield greater than 62 kt, an event in 1969, has an R value greaterthan 1.28. The decrease in precision, i. e. increase in R values, for events smaller thanabout 60 kt probably mainly reflects the smaller signal-to-noise ratios of the Lg wavesthat were used to determine m(Lg) at large distances.

These uncertainties in yield estimation, of course, pertain to precision and not nec-essarily to accuracy. Nevertheless, it seems unlikely that the calibration curves used inFig. I are more uncertain than either 0.07 in magnitude, 0.08 in log Y or a factor of 1.2in yield. The greatest contribution to the uncertainty of the yields determined by aver-aging magnitudes from Lg and P waves for explosions with yields larger than about 60kt comes from the uncertainty in the magnitude-yield calibration curve. Nonetheless,yields determined in this way for explosions larger than about 60 kt appear to have anaccuracy at 95% confidence that is comparable to and perhaps better than the factor of1.3 attributed to the Corrtex method for Shagan River explosions (Office of TechnologyAssessment, 1988). The published yield of 16 kt (Bocharov et al., 1989) for the explo-sion at Shagan River of February 10, 1972 agrees well with the yield of 18 kt (Table 1)obtained from mb'. This indicates that the calibration relationship and yield estimatesfor that test site near 20 kt from P wave magnitudes probably are of comparable accu-racy to those obtained from P waves alone for yields between 100 and 150 kt. At thepresent time the Corrtex method could not be used with confidence to determine yieldfor explosions smaller than several tens of kilotons (Office of Technology Assessment,1988). Thus, seismic methods offer a clear advantage in monitoring compliance undera Low-Yield Threshold Test Ban Treaty. The availability of digital recordings of Lgfrom regional stations in the Soviet Union, such as stations operated in conjunction withthe IRIS program, should result in greater precision in determining yield for tampedexplosions as small as about I kt.

Yields Determined from Surface Waves for Shagan River Explosions

Yields were also determined in Table I from surface waves for all moderate to largenuclear explosions at Shagan River for which digital data were available through the

9

end of 1986. With one exception, data of that type were available only after late 1978.Rayleigh wave (LR) and Love wave (LQ) amplitudes with periods in the narrow band18-21 s were measured on vertical and transverse component digital seismograms forlong-period stations in Eurasia. Only data for pure or nearly pure continental paths wereused so as to avoid complications resulting from surface wave propagation across con-tinental margins. The method of analysis for computing the surface wave magnitude,Ms, and station corrections are described in Sykes and Cifuentes (1984) and Sykes andEkstrom (1989).

It has been recognized for many years that many underground explosions at ShaganRiver trigger the release of natural tectonic stresses in the vicinity of the explosion shotpoint. Both the explosion source itself and the release of those stresses contribute to LRand Ms whereas only the latter contributes to LQ. Following our previous work on yieldestimation from Ms, we sought to make a correction to Ms so as to largely remove theeffect of tectonic release. This was done only for explosions with small to moderate tec-tonic release compared to the size of the pure explosion itself, i. e. for LQ / LR < 0.60,where that ratio was taken as an average over all stations used in the analysis. A fullmoment tensor solution is need for larger values of LQ/LR.

Yields were computed from

Ms + B(LR/LQ) = 2.16 + 0.97 log Y (4)

using the measured values of Ms, where the second term is a linear correction to Ms forthe effect of small to moderate tectonic release (Sykes and Cifuentes, 1984; Sykes andEkstrom, 1989). The relationship Ms = 2.16 + 0.97 was determined by Sykes and Cifu-entes (1984) using explosions of announced yield in various parts of the world for whicheither LQ/LR was small or the mechanism of the tectonic release was such as to not sig-nificantly affect Ms as averaged over a range to azimuths from the event. Values of Bwere obtained for each explosion at Shagan River of LQ/LR < 0.60 for which Ms wasavailable and Y had been determined from mb and/or mb(Lg). The average value, B =0.45, is close to the value 0.43 obtained by Sykes and Cifuentes (1984) for a muchsmaller number of events at Shagan River for which moment tensor solutions wereavailable at the time in the literature. That value is in accord with the hypothesis thattectonic release at that site involves predominantly thrust faulting and,hence, that thecorrection to Ms is positive. Also, the argument can be turned around taking B = 0.43from those moment tensor events to derive yields from surface waves that differ onlyslightly from those in Table 1. Those yields can then be used along with values of mb'for those explosions to calculate the constant in the mb-yield relationship for ShaganRiver. That constant is nearly identical to the two values obtained in Fig. I using a biasvalue of 0.35 mb units for the southwestern part of the Shagan River area with respectto NTS.

The individual values of log Y calculated from Ms (Table 1), however, scatter much

10

more when plotted against log Y determined from either mb' or mb(Lg) than is the casewhen the latter two quantities are plotted against one another. Thus, surface wave esti-mates of yield are less precise and, hence, are not used in this paper to calculate averageyields. They can be used, however, as a less accurate additional constraint on yield ifan estimate from Lg waves is not available or the average yield from P and Lg is nearor above the 150 kt threshold of the TTBT.

Yields of Weapons Deployed on Soviet Strategic Delivery Systems and Tested atShagan River

In November and December 1972 and in July 1973 the Soviet Union detonated threenuclear explosions at Shagan River with yields between 140 and 200 kt. Those eventsoccurred well before either the negotiations for the TTBT in July 1974 or the start datefor that treaty in 1976. The U.S.S.R. did not test again in the yield range above 120 ktat Shagan River until June 1979. A number of much larger explosions with yields of500 kt or greater were detonated at the two remote sites in Novaya Zemlya in the 20months between the signing of the TTBT and its start date. Those three events atShagan River were the only nuclear explosions detonated by the U.S.S.R. at any of theirtest sites in the yield range 120 to 400 kt from 1970 to June 1979, a period of a severalyears both before and after the signing of the TTBT (Sykes and Davis, 1987; Sykes andRuggi, 1989).

The occurrence of three explosions at Shagan River in that yield range within 9months of one another in 1972 and 1973 suggests that they represent the full yield ornearly full yield testing of important and distinct Soviet nuclear weapons. The use ofprecise methods of yield estimation from P and Lg waves permits an assessment to bemade of the yields of those three events and to compare them with the published yieldsfor the two events in 1972. The yields determined as an average of the log Y valuesfrom mb' and mb(Lg) are 154, 138 and 193 kt with associated R values (95% confidenceon precision) of 1.14, 1.22 and 1.22 kt respectively (Tables 1 and 3). The calculatedyields of the first two events agree closely with the announced yields (Bocharov et al.,1989) of 165 and 140 kt (Table 3). The explosion of July 23, 1973 of Y = 193 kt, forwhich the yield has not been released by the U.S.S.R., is clearly the largest undergroundexplosion at Shagan River.

Those three explosions occurred a few years before the initial deployment (Table 4)by the Soviet Union of their first MIRVed (multiple independently targetable re-entryvehicles) intermediate-range ballistic missiles (IRBMs) and MIRVed submarinelaunched ballistic missiles (SLBMs) according to Sykes and Davis (1987). The throw-weights of the SS-20, (the IRBM), and SS-N-18 mod 1, (the SLBM), and the number ofre-entry vehicles (three per missile) are consistent with warhead yields between 140 and200 kt (Sykes and Davis, 1987). SS-20 missiles have been destroyed under the termsof the Intermediate Nuclear Forces treaty; a number of SS-N-18 systems are still oper-

11

ational as of late 1991. Thus, one or more of the three largest nuclear tests at ShaganRiver in 1972 and 1973 appears to have been for the weapons to be carried by these twoimportant additions to the Soviet arsenal of strategic nuclear weapons.

Clustering of Yields of Shagan River Explosions

The newly calculated yields in Table I provide strong evidence of clustering in thedistribution of yields of Soviet tests at Shagan River from the start of the TTBT in 1976to mid 1988. The cumulative number of events at Shagan River during that interval withyields less than Y are plotted in Fig. 6 as a function of Y. The yield ranges centered on40, 88 and 138 kt, where the slope is greatest in Fig. 6, are associated wi" the most fre-quent testing at Shagan River. Additional tests with yields between 30 ancd : 00 kt duringthat period occurred at Novaya Zemlya as did a few others at the Degelen Mountain sitein Central Asia. Most tests smaller than about 30 kt during that time interval took placeat the Degelen Mountain portion of the Central Asian test site (Sykes and Ruggi, 1989).

The clustering of yields near 138 kt in Fig. 6 undoubtedly mainly reflects the artificialcutoff set by the 150 kt limit of the Threshold Treaty. Kidder (1985) shows a peak intesting by the United States from 1980 through 1984 at yields somewhat smaller than150 kt that is quite similar to the Soviet peak near 138 kt. He states that the "accumu-lation of [U.S.] tests near 150 kt is partly the result of testing, at reduced yield, strategicweapons whose yield would otherwise exceed the TTBT limit." Presumably, a similarlogic holds for at least some Soviet tests near 138 kt as well.

Soviet Compliance with the Threshold Test Ban Treaty

As yield estimates for Shagan River explosions have become more precise, the num-ber of events since 1976 with a yield determined from either P waves, Lg or their aver-age (Table 1) that exceeds 150 kt has become smaller. The maximum calculated yieldsof any of those explosions has decreased as well. For example, five events from 1976through mid-1988 have average yields in excess of 150 kt: 157, 158, 162, 169 and 170kt (Table 1). Each of those values is within a factor of 1.13 times 150 kt. Only the eventof July 1973, which occurred before the TTBT became effective, has a yield that isgreater than 150 kt at a high level of confidence. For two of those five explosions theaverage yield was based on mb' alone since Lg magnitudes were not available. A morecommon situation in Table I is for one of the two yield estimates to be above 150 kt,another below and the average somewhat below 150 kt. For example, the event ofDecember 10, 1972 had an announced yield of 140 kt, a yield from mb of 125 kt, thatfrom mb(Lg) of 153 kt, and an average calculated yield of 138 kt.

Thus, all of the explosions at Shagan River from the start date of the TTBT throughmid-1988 are consistent with Soviet compliance with that treaty. A similar conclusionwas reached by the Office of Technology Assessment (1988). Nevertheless, the new

12

estimates are still not accurate enough to ascertain a 10% or smaller exceedance of thethreshold with high confidence. For example, the event of November 2, 1972 with anannounced yield of 165 kt has an average yield of 154 kt and yields from P and Lgwaves of 144 and 165 kt. If any events since 1976 were in excess of the threshold bysmall amounts, the most likely candidates are 169 kt on August 18, 1979 and 170 kt onOctober 27, 1984. The explosion of July 1973, on the other hand, is a good example ofpresent capability to identify a past or future event with a yield in excess of about 190kt as being significantly larger than 150 kt at a high level of confidence.

Cavities Formed by Nuclear Explosions in Thick Salt Deposits that Might be Usable forFuture Clandestine Nuclear Testing

The U.S.S.R. has carried a number of nuclear explosions in salt near Azgir as wellas conducting several other PNEs in regions known to contain salt. Cavities producedby nuclear explosions in salt, such as Salmon and Gnome in the United States, haveremained standing for many years whereas cavities produced in other rock types usuallycollapse within short periods of time. Many investigators working on decouplednuclear testing that might be conducted under either a CTBT or a LYTTBT have paidconsiderable attention to the possible use of cavities produced by nuclear explosions. Iwill show, however, that monitoring of the relative few areas of the Soviet Union inwhich cavities of that type could exist that could be used in the future for either the fullor nearly full decoupling of explosions with yields larger than I kt is a tractable prob-lem. Instead, more attention needs to be devoted to the feasibility of decoupled testingin the yield range from I to 10 kt in large cavities produced by solution mining. Manymore potential sites are available in the U.S.S.R. for creating large cavities by solutionmining than are available from past nuclear explosions in salt.

Table 2 lists Soviet underground nuclear explosions that were detonated through 1986either in or in the general vicinity of thick salt deposits. As mentioned in earlier sec-tions, yields for explosions at Azgir were determined using recalculated mb values thatincluded station corrections derived for that site. Applying those station corrections toevents more than 100 km from Azgir, howe% :, did not reduce the standard error of themean of mb values for those events. Hence, -. tion corrections were not used in recom-puting mb for the other events in Table 2. The yields of all of the events in Table 2 werecalculated from (2).

Nine of the explosions at Azgir have yields between 25 and 110 kt. All of thoseevents occurred between July 1, 1968 and October 24, 1979 in the area of numerous saltdomes to the north of the Caspian Sea, what Soviet workers call the Pri-Caspian region.I will now make estimates of the sizes of decoupled nuclear explosions that could bedetonated in cavities created by those and other Soviet nuclear explosions located eitherin or in the general vicinity of thick salt deposits. The conservative assumption will bemade that cavities, in fact, remain standing for all of those events and that they could be

13

used for conducting small decoupled nuclear tests at some time in the future. First,information about the depths and dimensions of the cavities created by the U.S. explo-sion Salmon and two explosions at Azgir is used to calculate yields of nearly decoupled(Sterling conditions) and fully decoupled nuclear explosions that could be conducted inthe cavities assumed to have been created by the Soviet events in Table 2.

Salmon, a fully-tamped explosion of 5.3 kt, was detonated in a salt dome in the stateof Mississippi at a depth of 828 m in 1964. The Sterling nuclear explosion was a decou-pled event of 0.38 kt detonated in the Salmon cavity at the same depth in 1966 (Dennyand Goodman, 1990). The Salmon cavity, like that produced by the Gnome explosionin bedded salt in New Mexico and that produced by the tamped Soviet explosions of1966 and 1968 in salt domes, was not perfectly spherical in shape. In each case a sig-nificant amount of rubble and molten salt accumulated at the bottom of the initiallynearly spherical cavity. The cavity volume for the Sterling event was 19,400 m3 , givinga mean radius 16.7 m (Denny and Goodman, 1990). The 1968 Azgir event of 25 kt wasdetonated at a depth of 590 m and produced a cavity with a volume of 140,000 m3, giv-ing a mean radius of 32.2 m (Kedrovskiy, 1970). The 1966 Azgir explosion of 1.1 ktwas detonated at a depth of about 165 m and generated a cavity with a volume of 10,000m3 (mean radius of 13.4 m). Since that cavity filled with water (Kedrovskiy, 1970), itobviously could not be used for detonating decoupled explosions unless the water couldbe removed. The Soviet explosion at Orenburg of October 22, 1971 of 15 kt in beddedsalt was used to produce a cavity for storing gas condensates at an unspecified depth.Its volume was 50,000 m3, giving a mean radius of 22.9 m (Izrael' and Grechushkina,1978).

The requirement that a clandestine nuclear test in a large underground cavity in salt

not produce a crater or other disturbance at the surface and that it be fully contained so

as not to leak radioactive products to the surface set limits on the minimum depth of

such a cavity. For a very weak material like salt, Latter et al. (1961) conclude that the

pressure on the cavity wall for full decoupling must be less than or equal to one half the

overburden pressure (i.e. the vertical stress, pgh) so as to prevent failure in tension of

the surrounding salt material and, hence, to prevent leakage of radioactive gases from

the cavity. The relationship between a step in cavity pressure, P, produced by an explo-

sion of yield, Y, in a cavity of volume, V, and the requirement for containment that P

be less than some constant, k, times the vertical stress can be written

P= (y-I)Y/V < k pgh (5)

14

where y is the ratio of heat capacities taken to be 1.2 under the conditions of interest

(Latter et al., 1961), p is the average density of the material from the surface down to

depth, h, and g is the gravitational acceleration at the earth's surface. The average den-

sity in the following applications is taken to be that of salt at the Salmon site, 2200 kg /

m 3.For the Latter criterion mentioned above, k = 0.5.

Taking k = 0.5 and the relevant parameters for the cavities created by the Salmon andthe 1966 and 1968 Azgir explosions, the maximum yields of fully decoupled explosionsaccording to the Latter criterion that could be detonated in those cavities (after convert-ing the energy in Joules, J, to kilotons, where I kt = 4.184 x 1012 J) are 0.21, 0.02 and1.1 kt respectively. The ratios of the size of the tamped nuclear explosion that was usedto create each of those cavities to the size of the largest fully decoupled event that couldbe detonated in them under the Latter criterion are 25, 55 and 23 for the Salmon, 1966and 1968 events.

Sterling was almost, but not fully decoupled; P was a factor of 1.8 = 0.38 / 0.21 timeslarger than that calculated by way of the Latter criterion. The value k = 0.90 calculatedfor that event indicates that P still did not exceed the vertical stress (k = 1). Experiencewith cavities in salt used for gas storage indicates that leakage of the storage productmay occur when the internal pressure in the cavity exceeds the vertical stress. If Ster-ling conditions, i. e. k = 0.90, apply rather than the Latter criterion to the 1966 and 1968cavities at Azgir, maximum yields for explosions that could be detonated in those cav-ities are 0.04 and 2.0 kt. The ratio of the size of the tamped nuclear explosion that wasused to create a cavity to the size of the largest decoupled event that could be detonatedin them under what I will term Sterling conditions is 13.9 = 5.3 / 0.38 for the Salmon /Sterling pair and 27 and 12.5 for the 1966 and 1968 explosions at Azgir.

Thus, much larger (12 to 55 times larger) tamped explosions are needed to createcavities than the maximum sizes of either fully decoupled or nearly fully decoupledexplosions that can be detonated in them. This is important since, even at the unclassi-fied level, the United States knows of all past Soviet underground explosions down to asmall yield that have been detonated either in or possibly in areas of thick salt deposits.The yields of fully decoupled and nearly fully decoupled explosions that could be det-onated in cavities that may remain standing from those events is at least an order of mag-nitude smaller than the yields of the explosions that generated those cavities.

While the cavity volume produced by a tamped explosion undoubtedly varies withthe depth of the event, it should be appreciated that fully decoupled and nearly fullydecoupled nuclear explosions larger than I kt would have to be conducted in a fairly nar-row range of depths. An air filled cavity in salt is likely to deform significantly at depthsgreater than 1000 m whereas an evader determined not to be caught testing at suchyields, would use only cavities that are at least several hundred meters deep to insurethat bomb-produced products did not escape from the cavity. There is a tradeoffbetween the fact that a shallower tamped explosion produces a larger cavity than a

15

deeper one in the same material and the fact that a larger cavity at a shallower depth isneeded to satisfy inequality (5) for a decoupled event of a given yield.

Since the depths of most of the explosions in Table 2 are not known, two estimatesof the yields of fully decoupled and nearly fully decoupled nuclear explosions that couldbe detonated in cavities created by those events have been made in the last column ofTable 2. The smaller value is derived by dividing the computed yield of each event inTable 2 by the yield ratio 5.3 / 0.21 = 25, where 5.3 is the yield of Salmon and 0.22 isthe computed yield by the Latter criterion of the largest fully decoupled yield that couldbe tested in the Salmon cavity. The larger yield in the last column is computed by divid-ing the calculated yields of each event in the table by the yield ratio for the Salmon /Sterling pair = 5.3 / 0.38 = 13.9. Those simple calculations--1.0 and 1.8 kt--for the cav-ity produced by 1968 Azgir event of 25 kt are very close to the values obtained aboveusing the published depth and volume for that cavity-- 1.1 and 2.0 kt. The simple calcu-lations for the much smaller 1966 event overestimate the yields calculated above fromthe depth and volume of that cavity.

The yields of the various events in Table 2 divided by 13.9 (larger numbers in lastcolumn) are taken as a measure of the yields of nearly fully decoupled explosions thatcould be detonated in the cavities produced by those events. This, of course, assumesSalmon / Sterling conditions. Uncertainties in the yields of the events that producedthose cavities and their depths can lead to uncertainties in the estimates of decoupledyields by a factor of 1.5. Our main concern here, however, is what are the "opportuni-ties" that may be available to test weapons clandestinely of certain approximate sizesand not that exact size.

Table 5 summarizes the yields of nearly fully decoupled (Sterling conditions) nuclearexplosions that could by detonated in the cavities of events in Table 2 both by area andyield range. Most of the "opportunities" for such testing are concentrated in the area tothe north of the Caspian Sea. The "oppontunities" for the larger tests, up to a maximumof 7 to 8 kt, are mostly confined to Azgir itself. Possibilities for such decoupled testingare more restricted in the area of bedded salt to the northwest of lake Baikal. Some andperhaps all of those events may not have been conducted in salt but in other rocks in thestrategraphic sequence or in rocks just outside the area of salt deposits. Once again, thislist attempts to be conservative in its cataloguing of potential areas and sites for decou-pled testing in the range I to 10 kt. For example, the single Bukhara event (Tables 2 and5) was used to put out a fire in an oil well that had encountered an unanticipated faultthat had provided pathways for escaping petroleum. It was also detonated at such agreat depth (2.5 km) that closure of the salt cavity undoubtedly occurred soon after itwas detonated. Thus, on both of those grounds it appears to be a poor and risky candi-date site for conducting a clandestine decoupled nuclear explosion.

Thus, the number of cavities produced by past nucler explosions that potentiallycould be used for clandestine testing of nearly fully decoupled nuclear explosions undereither a CTBT or a LYTTBT is limited. Those sites are confined to a few areas of the

16

k~~~~~~~~~~~~~1 : - - : 1 : - _71 :% ,' - - -I r ,:7 " : 3'' ?: ' . . : '

%

U.S.S.R. The question of using those cavities instead for partially decoupled events asdescribed by Stevens et al. (1991) will be dealt with in a separate paper along with thefeasibility of constructing and using cavities in hard rock for either the full or the partialdecoupling of explosions with yields from 1 to 10 kt. Possibilities of clandestine testingin large cavities created by solution mining also will be dealt with in a separate paper.

CONCLUSIONS AND RECOMMENDATIONS

Implications for Identifying Small Decoupled Nuclear Explosions in Salt

For purposes of appreciating the detection capability of a given seismic network, itis important to recognize, using data from Azgir, that a fully-coupled (tamped) explo-sion of I kt in salt in high-Q areas of the U.S.S.R. has an mb of 4.46; fully decoupledevents of 1 and 10 kt have mb's of 2.61 and 3.40 respectively (assuming a decouplingfactor of 70). These magnitudes are higher than has generally been thought previously.For example, chemical explosions of mb < 2.6 in high Q areas containing salt need notbe considered in monitoring a 1 kt threshold treaty. Most areas of thick salt deposits inthe U.S.S.R. are typified by high Q (efficient transmission) for P waves and low natu-ral seismic activity.

Past nuclear explosions conducted in salt by the Soviet Union for which cavities mayremain standing that are large enough for the full decoupling of explosions larger than1 kt are concentrated in only a few areas of that country. The existence of all cavities ofthat size or larger that have been created by past nuclear explosions is known (Table 3)since the explosions that created those cavities must be about 25 times larger in yieldthan the size of the fully decoupled event that can be detonated in them. (That ratio is13.9 for the Salmon/Sterling pair where the yield of Sterling was about 1.8 times largerthan that of a fully decoupled explosion in the Salmon cavity).

Hence, the monitoring of cavities of that size that may remain standing that werecreated by past nuclear explosions should be relatively easy under a Low-Yield Thresh-old Test Ban Treaty with a threshold of I kt, providing U.S. stations are allowed to oper-ate under the treaty near the epicenters of those past explosions. Probably the greatestdifficulty in monitoring such a LYTTBT involves cavities created, not by nuclear explo-sions, but by solution mining in other areas of thick salt deposits of the U.S.S.R.

Precise Yield Estimates for Explosions at Shagan River

Yield determinations for Shagan River explosions can be improved by subdividing

17

t ~ m mn N m~ mm~

that testing area into three parts with different mb-yield relationships and by combiningthose results with yields calculated from Lg. The calculated yields of many of those

explosions since 1976 are clustered in a few specific ranges of yield.

18

RZFERENCE8Bocharov, V.S., S.A. Zelentsov and V.N. Mikhailov (1989). The

characteristics of 96 underground nuclear detonations at theSemipalatinsk test range, ktomic Energy 67, 210-214.

Denny, M.D. and D.M. Goodman (1990). A case study of the seismicsource function: Salmon and Sterling reevaluated, J. Geophys.Res. 95, 19, 705-19, 723.

Der, Z., T. McElfresh, R. Wagner and J. Burnetti (1985). Spectralcharacteristics of P waves from nuclear explosions and yieldestimation, Bull. Seismol. Soc. Amer. 75, 379-390, 1222.

Hanson, R.A., F. Ringdahl and P. G. Richards (1990). The stabilityof RMS Lg measurements and their potential for accurateestimation of the yields of Soviet underground nuclearexplosions, Bull. Seismol. Soc. Amer. 80, 2106-2126.

Izraehl, Yu. A. and M.P. Grechushkina (1978). The use of peacefulunderground nuclear explosions with minimum radioactivecontamination of the environment, Peaceful Nuclear Explosions V,International Atomic Energy Agency, Vienna, document IAEA-TC-81-5/7, pp. 167.

Kedrovshiy, O.L. (1970). Prospective applications of undergroundnuclear explosions in the national economy of the USSR, UCRL-Trans-10477, (Translation from Russian), Lawrence RadiationLaboratory, University of California, Livermore, CA, 1-47.

Kidder, R.E. (1985). Militarily significant nuclear explosiveyields, F.A.S. Public Interest Report, (Journal of Federation ofAmerican Scientists)38, no. 7, pp 1-3.

Laftei, A.L., R.E. LeLevier, E.A. Martinelli and W.G. McMillan(1961). A method of concealing underground nuclear explosions,J. Geo.hys.Res.66, 943-946.

Marshall, P.D., T.C. Bache and R.C. Lilwal (1984). Body wavemagnitudes and locations of Soviet underground explosions at theSemipalatinsk test site, Atomic Weapons Research EstablishmentReport 0 16/84, 1-87.

MarsaIT, P.D., D.L. Springer and H.C. Rodean (1979). Magnitudecorrections for attenuation in the upper mantle, Geophys. J.R.Astr. Soc. 57, 609-638.

Office of Technology Assessment, Congress of the United States(1988). Seismic Verification of Nuclear Testing Treaties OTA-ISC-361, U.S. Government Prting Office, Washington, DC, 139 pp.

Ringdal, R. and P.D. Marshall (1989). Yield determination of sovietunderground nuclear explosions at the Shagan River test site,Semiannual Tech. Summary 1 October 1988-31 March 1989, NORSARSci. Rpt 2-88/89, Kjeller, Norway, pp. 36-67.

Ringdal, F. (1989). NORSAR P-wave detection and yield estimationof selected Semipalatinsk explosions, Semmiannual Tech. Summary1 April-30 September 1989, NORSAR Sci. Rpt. 1-89/90, Kjeller,Norway, pp. 54-61.

Ringdal, F. and J. Fyen (1988). Comparative analysis of NORSAR andGrafenberg Lg magnitudes for shagan River explosions, SemiannualTech. Summary 1 April-30 September 1988, NORSAR Sci Rpt. 1-88-89, Kjeller, Norway, pp. 88-106.

Stevens, J.L., J.R. Murphy and N. Rimer (1991). Seismic sourcecharacteristics of cavity decoupled explosions in salt and tuff,Bull. Seismol. Soc. Amer. 81, 1272-1291.

19

Sykes, L.R. and I.L. Cifuentes (1984). Yields of Soviet undergroundnuclear explosions from seismic surface waves: compliance withthe Threshold Test Ban Treaty, Proc. Natl. Acad. Sci. USA, 81,1922-1925.

Sykes, L.R. and D.M. Davis (1987). The yields of Soviet strategicweapons, Sci. Amer., 256 29-37.

Sykes, L.R. and d.- Ekstrom (1989). Comparison of seismic andhydrodynamic yield determinations for the Soviet jointverification experiment of 1988, Proc. Natl. Acad. Sci. USA, 86,3456-3460.

Sykes, L.R. and S. Ruggi (1986). Soviet underground nucleartesting: inferences from seismic observations and historicalperspective, Working Paper NWD 86-4, Natural Resources DefenseCouncil, Washington, DC, 88 pp.

Sykes, L.R. and S. Ruggi (1989). Soviet nuclear testing, in SovietNuclear Weapons, Nuclear Weapons Databook, IV, T.B. Cochran etal (editors), Ballanger, New York, 332-382.

20

-NEVADA-GraniteS6.2 (D- NEVADA- below water table< n soft rock, Y 90ktCU Longshot -Andesite

*6.0 -*-Salmon-Salt+ALGERIA-Granite + 0

X - U.S.S.R.- Shagan River/5.8 A-US.S.R.-Azqir, Salt /d

0 d -Degelen Mt. 4 Mb: 4.483o) m - Murzhik / m 0.787 logY-

~ 5.6 Adn=17

0

(I)b-

5.2 -m 150 kt-d TTBT limit

Nd

Et-0 /

o4.6- ,4 ~ mb 4.463 + Q804 logYA' n 13

12 3 5 10 30 50 100 200Y, Yield (kt

Fig. 1 Calibration curves used for yield estimation as normalized to Southwesternportion of Shagan River testing area. Explosions at Degelen and Murzhik werenot used in two regressions. Explosions used are those of published yield in eitherhard rock or below water table.

21

+++ +

+ 0 +•

++

.0+.

0 +*+* 0*

++I~

.0 ""

.4 *

44 0 4

• -

.4 *.4 *00.4 * 0

too

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22

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SW SHAGAN

6.?

o

SD .046 o0

5.9

%o

E0

5,

3 5 6

5 9 6 .2

6.5

m b = m

Fig. 3 Lg magnitude as a function of body wave magnitude for southwestern portion ofShagan River testing area. SD = standard deviation.

23

6.5 ALL SHAGAN RIVERSUB -AREAS

6.2 0

mb'= 1.090 m(Lg) - 0.440 0

SD= .069

5.9 % 00

0 0 002 0

5.6

00

00

5.3

0

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Fig. 4 Lg magnitude as a function of revised body wave magnitude, mjb'. SD = standarddeviation.

24

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41

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(27

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N NN 0 14 C N N 010.4 0 N N 4 NN

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w0 00000000ww o w00 w0 0 00w0 40000WM D00 00 WW0 00MM00 00C 000D 0 00 000 0000O WODO

28

I= 0

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29

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31

9 9.9 9 9 9 9; 999 99 9Ln -T b~ Iq bn vn m' C4 m

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+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 .: +1 +1 +1 +1

an, an an Ln In In an an I* In in tn in n a an n

ae n an an le lw t ~ n an an IV v

an an an an in an an a n an an an an an an I

0 to a.o6 W a t

.X~~4 2m W* 2 2 CC w.

32

Table 3: Largest Shagan River Underground Explosionsprior toJune 1979 of Yield > 125 kt

Date Yield (kt)Announced Calculated

02 Nov. 1972 165 15410 Dec. 1972 11 140 13823 July 1973 -- 193

Table 4: Major Soviet Missile Systems with Throw-weightsAppropriate to above Yields

System First Deployment #RVs Comments

SS-20 1977 3 First Soviet MIRVed IRBMSS-N-18 mod 1 1978 3 First Soviet MIRVed SLBM

33

Table 5. Number of cavities that may remain standing from Soviet Underground NuclearExplosions form 1%1 to 1986 within and near salt deposits that might be useful forconducting nearly fully decoupled nuclear explosions with yields greater than 0.5 kiloton.(Obtained from calculated yield of known explosion at site divided by yield ratio forSalmon/Sterling explosions = 5.3/0.38=13.9.)

Area of Known Salt Deposits Maximum Nearly Fully Decoupled Yield (kt)

0.5-1 1-2 2-3 3-4 4-5 5-7 7-8 >1. North Caspian Region

a. Azgir 1 1 1 2 1 2b. Astrakhan 9* 1c. Other 6 2 1 1

2. a. Central Siberian Platform(northwest of Lake Baikal) 4

b. Within a few hundredkilometers of layered saltdeposits 1 1 1

3. Bukhara I, Central Asia(explosion used toextinguish fire in oil well)

Total 20 5 3 2 3 1 2 0

* Many small nuclear explosions at nearly the same location. Cavities conceivably

could be interconnected to form a larger cavity

34

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