Explosive Yield Research Articles

Estimating the yield of underground nuclear explosions

abstract Estimating the yield of underground nuclear explosions from the far-field seismic waves is a difficult problem, since accurate estimates require a detailed accounting for source-region and travel-path differences between known and unknown yield events. For short-period P waves, the first problem is to obtain an unbiased measure of the far-field energy. Conventional m b seem unsatisfactory because of the large scatter in station values. The dominant cause seems to be wave focusing/defocusing by complex earth structure. Improved routine measures are likely to involve measurements of the spectral energy in the initial P and/or P coda. Direct modeling of recordings from especially good stations can also provide important information. Even with an unbiased measure of far-field energy, bias in yield estimates can result from regionally varying path effects (mainly attenuation) and variations in the source-coupling properties of the local geology. The effect of attenuation differences is difficult to quantify for specific events due to strong tradeoff with source-coupling and complex earth structure effects. Detailed computer models for the effect of material properties on coupling are able to match most of the available data, but their validity for extrapolation to other materials is questioned because of problems with uniqueness and independent verification of the model parameters. The NTS volcanic materials are best understood. The major unresolved problems are with granite and salt, where the bulk material strength at the large scale of nuclear explosions controls the coupling and is very difficult to estimate. For surface waves, the issues are analogous, except for the additional complication of nonisotropic effects that sometimes dominate the radiation. Otherwise, it appears that surface waves should give more precise estimates for large events. Yield estimation is, in practice, done with some empirical relationship based on known yield events. This is briefly discussed to indicate that, despite the many technical problems, m b and M b data scale rather well with yield. The main objective of the paper is to summarize the current state of understanding of the technical issues and highlight the important questions.

Test ban treaty verification with regional data—A review

abstractThis paper summarizes the use of regional (Δ ≦ 30°) seismic data in a test ban context for detecting, locating, identifying, and determining the yield of underground nuclear explosions. In many areas of the world (Eastern North America, Africa, Eastern USSR), Lg is the largest amplitude wave recorded on standard seismograph systems and thus is the most appropriate phase for monitoring small magnitude events. Excellent location capability for near-regional events has been demonstrated at the Norwegian small aperture array (NORESS) using Lg and P waves. Lg and other regional phases may contain information on source depth, but such information has not been exploited to date. Fifteen classes of regional discriminants have been identified includingEach of these proposed discriminants has, with differing degrees of success, separated some explosions from some earthquakes. However, most have been tested only on limited data, usually from one geographic region and only one or two recording stations. No systematic analyses have been done to determine the best individual discriminant or combination of them.Preliminary evaluation of the use of Lg for yield determination suggests that regional waves hold promise in this application. Theoretical studies have contributed significantly to the understanding of propagation characteristics of regional waves but further studies are required emphasizing modeling for realistic anisotropic sources.The major conclusion of this study is that a systematic and comparative evaluation of all the proposed regional discriminants is now required, utilizing a common data base derived from all present-day test sites. This evaluation would suggest the optimal discrimination procedure using regional waves, and would also define areas of needed research. Without such an integrated evaluation, it is still possible to speculate, using existing results, on the most promising regional discriminants.

Explosive desensitization studies via chemical group modification. Nitroso‐Derivatives of RDX and 3‐Amino‐TNT

AbstractWith aims toward desensitizing RDX and TNT via molecular modification, mono‐ and trinitroso‐derivatives of RDX and 3‐amino‐TNT were synthesized and subjected to sensitivity tests. Impact and shock sensitivity data show these compounds to be markedly desensitized. Explosive yield measurements indicate that the changes in power output due to these molecular modifications are minor.

Mount St. Helens Eruption of 18 May 1980: Air Waves and Explosive Yield

Strong atmospheric acoustic-gravity waves were recorded by sensitive microbarographs and seismographs at large distances from the Mount St. Helens eruption of 18 May 1980. Wave signatures were similar to those of waves from large nuclear explosions. Independent theoretical and empirical analyses indicate that the explosive yield of the eruption was approximately 35 megatons.

Microprocessor-controlled time domain reflectometer for dynamic shock position measurements

Time-domain reflectometry is used in a novel way to dynamically measure shock propagation in various media. The primary component in this measurement system is a digital time domain reflectometer, which uses local intelligence, a Motorola 6800 microprocessor, to make the unit adaptable and versatile. The recorder, its operating theory and its method of implementation are described and typical data are reviewed. Applications include nuclear explosion yield estimates, and explosive energy flow measurements.

T-phase recordings at Rarotonga from underground nuclear explosions

Summary Exceptionally strong T phases, with amplitudes up to 30 times greater than those of the associated P phases have been recorded at the Rarotonga seismograph station from underground nuclear explosions detonated in French Polynesia since 1975. Later arrivals in the T wavetrain are identified as reflections from neighbouring islands, and the slow velocity of T-phase propagation enables various source areas in French Polynesia to be differentiated. The lack of correlation between T-phase amplitude and explosion size suggests a saturation of the T-phase propagation mechanism close to the source. T-phase durations have been used to estimate the seismic yield of the underground explosions.

A study of detonation in methane/air clouds

In the present paper, we study the problem of detonation in unconfined, gaseous mixtures of methane/oxygen/nitrogen. A numerical simulation approach is employed in which we use a one-dimensional (spherical symmetry), time-dependent computer model to simulate the coupled compressible fluid dynamics-chemical kinetics processes which occur upon direct initiation of detonation. We establish the magnitude of explosive yield of tetryl required to initiate detonation in mixtures of CH 4 + 2O 2 with varying degrees of nitrogen dilution, up to and including stoichiometric CH 4 air . The numerical simulations illustrate the features of direct initiation observed in many experimental investigations, e.g. shock-wave breakaway followed by detonation reestablishment via a quasi-steady, oscillatory flow regime which occurs before the establishment of a steadily propagating spherical detonation. Our results compare well with recent experimental data obtained by Bull et al. (1976) over the range of tetryl masses studied by them. We find that tetryl explosive masses in excess of 10 7 grams would be required to initiate detonation in an unconfined, stoichiometric CH 4 air mixture.

A back-of-the-envelope approach to predicting ground motion phenomena

An analytic model (Bote model) is presented as a means to describe the pressures at and arrival time of the spherically diverging stress wave resulting from an underground explosion. The model is based on a linear combination of the forms used to describe the two extremes in the stress wave lifetime: a strong shock at early times and a simple elastic wave at late times. The Bote model traces the propagation of the spherically diverging stress wave through the hydrodynamic, plastic, crush-up, and elastic pressure regimes and predicts the pressures at and arrival times of the shock front. While able to account for the effects of porosity and water content of the surrounding medium, the Bote model requires knowledge of only two points on the pressure-volume (PV) curve of the medium: the pressure PE below which the medium is assumed to behave elastically and the pressure PC at which all air-filled voids in the medium have been crushed out. Simple expressions are given for determining PC and PE as a function of water content and gas fill porosity. Other necessary Bote model inputs include explosive yield (Y) and medium type as well as geologic characteristics, including grain density (ρg), in situ density (ρ0), water content (W), and sound speed (C). Compared with both calculated and measured ground motion data, Bote results show good agreement for times ranging from tens of microseconds to tens of milliseconds, for distances out to a scaled range of 107 m/kt1/3, and for pressures to of the order of 105 Pa.

Seismic source and transmission functions from underground nuclear explosions

abstract A model is presented for the simultaneous detemination of the relative variation in transmission properties to different stations and of the relative differences between the seismic sources for closely spaced underground nuclear explosions recorded by a fixed seismological station network. The model is applied to short-period data reported from 24 globally distributed stations from 12 underground nuclear explosions with known yields at Nevada Test Site. The obtained transmission functions vary within a factor of 10 between the different stations and show a weak decrease with epicenter distance and little correlation with the Gutenberg amplitude-distance curve. The relative source functions for 10 explosions in tuff and rhyolite, with yields in the range 16 to 1,200 kt, are with good correlation proportional to explosion yield to 0.9. Two theoretical source-function models, one by Haskell (1967) and one by Mueller and Murphy (1971a), are compared with each other and they agree well for frequencies around 1 Hz and for yields in the range 3 to 300 kt. The Haskell model for tuff is modified to be more compatible with the models for salt, granite and alluvium. The Haskell model predicts stronger variation of the source functions with frequency and yield than the Mueller-Murphy model. The observed relative source functions are compared with the theoretical source functions obtained from the two source models. The agreement is fairly good but the relative decrease of the source functions at yields above 300 kt predicted by the theoretical models is not observed.

Theoretical Effect of Yield and Burst Height of Atmospheric Explosions on Rayleigh Wave Amplitudes

Theoretical seismograms for fundamental mode Rayleigh waves were calculated for atmospheric point sources over oceanic and over continental Earth models, as recorded at an epicentral distance of 10000 km. Yields were uniformly distributed over the range 1 kT-10 MT, for source altitudes in the range 0.3-92.0 km. The Earth structures used were those of Gutenberg and of Anderson and Toksoz. The source models were point mass-injection and energy-injection sources at altitude, as well as a distributed pressure pulse at the surface of the Earth. It was found that: (1) as far as Rayleigh wave excitation is concerned, the mass-injection and energy-injection sources are equivalent; (2) for low altitudes the Rayleigh wave excitation is independent of source type, but at intermediate altitudes the surface overpressure source predicts greater amplitudes than the other two source models; (3) for most altitudes, the energy coupling from the atmosphere into Rayleigh waves is more efficient for the continental Earth structure than for the oceanic structure; (4) Rayleigh wave amplitude is more sensitive to yield than to burst height (5) dependence of Rayleigh wave amplitude is less than the cube root relation for low-yield explosions at intermediate altitudes but greater for high-yield explosions at near-surface altitudes; (6) spectral splitting ratios do not show a systematic variation with yield and burst height.

Multiple Discriminant Screening Procedure for Test Ban Verification

A DECADE of research has led to a well defined capability for the seismological method of verification of compliance with a ban on underground nuclear explosions. Whatever political form the treaty will eventually have, it is generally agreed that decisions concerning violations will be national decisions. Recent presentations to the Conference of the Committee on Disarmament in Geneva1–4 lead us to consider in some detail utilisation of the seismological discrimination experience in a national operational verification procedure. The thrust of the sample operational procedure to be described depends on an acceptance of the fact that detailed consideration of clandestine explosions, or evasion tactics in general, is futile until all natural seismic activity can be identified down to the required seismic magnitude or equivalent explosion yield. Thus, the operational procedure becomes an earthquake screening process that can be tested in simulation in advance of the Test Ban Treaty.

The Effect of Nuclear Stimulation on Formation Permeability and Gas Recovery At Project Gasbuggy

At Project Gasbuggy, permeability was affected for some 220 feet beyond the chimney. However, irrespective of the permeability of the close-in region and of chimney size, gas eventually must flow into the chimney from the outer reaches of the drainage area of the well. Thus the preshot formation permeability is a highly critical factor in calculating anticipated recovery from nuclear stimulated reservoirs. Introduction Project Gasbuggy is a joint experiment by the Atomic Project Gasbuggy is a joint experiment by the Atomic Energy Commission, the Dept. of the Interior, and the El Paso Natural Gas Co. to investigate the feasibility of using underground nuclear explosives to stimulate production and increase ultimate recovery of natural gas from a low-permeability gas-bearing formation. The low-permeability Pictured Cliffs formation found in the San Juan basin of the Four Corners area of New Mexico, Arizona, Utah, and Colorado was selected for the experiment. The actual test site is about 55 miles east of Farmington, N. M., in the southwest quarter of Sec. 36, T29N, R4W, Rio Arriba County (Fig. 1). To supplement reservoir and production data available from the eight original field wells in the Gasbuggy test area, two preshot test wells, GB-1 and GB-2 (Fig. 2), were drilled in 1967. Extensive production tests were conducted on GB-1. The Project production tests were conducted on GB-1. The Project Gasbuggy nuclear explosive of 29-kiloton yield was detonated on Dec. 10, 1967, at a depth of 4,240 ft, approximately 40 ft below the base of the Pictured Cliffs formation (Fig. 3). Postshot re-entry of the emplacement hole, designated as GB-ER, began on Dec. 12, 1967, and terminated at a total depth of 3,916 ft on Jan. 10, 1968. Initial computations indicated a collapsed chimney about 160 ft in diameter extending from the 4,240-ft detonation depth to about 3,900 ft, the top of the 300-ft-thick Pictured Cliffs gas sand. In addition to GB-ER, preshot well GB-2 was reentered as GB-2RS, and a new well, GB-3, was drilled in 1969 at a surface distance of 250 ft from GB-ER. GB-ER has undergone extensive testing covering a period of 3 years. During this period, pressures were monitored in GB-2RS and GB-3. Presented in this paper is an analysis of the effectiveness of nuclear stimulation on increasing the formation permeability and the resulting gas recovery at Project Gasbuggy as determined from a flow model. Effect on Reservoir Rock Studies of a number of contained underground nuclear explosions have yielded a rather consistent representation of the geometric features produced. The items of primary interest related to the breakage and displacement of rock resulting from a nuclear stimulation include (1) chimney configuration, (2) chimney void volume, (3) chimney permeability, and (4) permeability of the rock outside the chimney. Boardman has discussed these as a function of explosive yield, depth of burst, and rock type. The chimney configuration and chimney void volume as reported by Boardman and by Atkinson et al. are in close agreement. As to the permeability in the chimney and the permeability outside the chimney, Boardman reported no quantitative answer. For the nuclear stimulation of hydrocarbon reservoirs, as for other stimulation processes, the quantitative value of the permeability increase outside the chimney is vital to the prediction of the ultimate recovery of hydrocarbons. JPT P. 1199

An energy approach to seismic coupling analysis

The explosion process is modeled by a step change in cavity pressure. The cavity is assumed to be spherical and embedded in an ideal elastic solid. This model represents a fully decoupled explosion in a cavity. It can also be used as an equivalent seismic-wave source representing a tamped explosion. A decoupling cavity existence and operating region is defined in terms of cavity and overburden pressures and the rock yield strength. The upper limit for seismic coupling efficiency for an ideal monoatomic gas is given by Ew/Ex = 2Y/3μ, where Ew is the radiated seismic-wave energy, Ex is the explosion yield, Y is the rock yield function, and μ is the shear modulus. This equation may be a good approximation for the seismic-coupling efficiency of a tamped explosion, because it agrees well, perhaps fortuitously, with observations for tamped nuclear explosions in salt and granite. The seismic-energy radiation from a spherical cavity in an elastic medium is given by Ew = 2πPχ, where P is a step change in cavity pressure and χ is the final value of the reduced displacement potential. This equation shows that the seismic-coupling efficiencies of French nuclear explosions in Sahara granite may be about equal to those of U.S. shots in Nevada granite, even though the cavity radii, elastic radii, and reduced displacement potentials for these two sets of explosions (assuming equal yields) are quite different. The theoretical seismic-energy spectra for the Nevada and the Sahara explosions are consistent with the measured spectrum for the 5-kT Hardhat explosion and overlap to a significant degree. This overlap is centered in the 0.5- to 5-Hz bandwidth and may partially explain why nuclear explosions in Nevada and Sahara granites appear to have the same magnitude-yield relation. The possibility of regional variation of seismic-signal attenuation in the upper mantle of the United States and the Sahara should also be investigated to complete the explanation of seismic coupling in Nevada and Sahara granite.

Discrimination Between Earthquakes and Underground Explosions Employing an Improved Ms Scale

Summary The M, Rayleigh wave magnitude formula is revised for purposes of eliminating the heretofore variable effects of near distances and propagation paths on the values computed from standard long-period seismograms. The improved formulation employs a revised distance correction function and a period-dependent path correction that normalizes M, to large teleseismic distance 20-s values. For purposes of earthquake-explosion discrimination, an empirical focal depth correction is derived on the basis of Rayleigh wave frequency content as a function of focal depth, which normalizes M, values to the surface focus equivalent, i.e. aids discrimination when it can be applied by increasing earthquake M, values and moving them away from the equivalent explosion population on M, : m, plots. The revised M, improves on previously achieved discrimination of North American events, and provides reliable discrimination between suites of Eurasian earthquakes and explosions. Having removed the dominant propagation path effects on M,, the residual differences in M, : mb among events are generally attributed to source environment and regional effects on m,,. The 42 Eurasian WWSSN stations employed are shown to have a discrimination threshold at the M,3.2 level. With the improved M, scale now equivalent to first order for North American and Eurasian continental propagation, available Nevada Test Site explosion yields are extrapolated to the Eurasian sites to illustrate that this M,3.2 discrimination threshold is equivalent to an Eurasian explosion of about 20 kt in hard rock. Given improved long-period instrumentation to reduce the Rayleigh wave detection threshold, the principal restriction on further studies of discrimination to lower levels of magnitude and yield will be the availability of earthquake occurrence information at the low magnitudes.

Project Rulison—Summary of Results and Analyses

The results of Project Rulison confirm the technical feasibility of stimulating the Mesaverde formation in the Rulison Field with nuclear explosives.Testing of the nuclear stimulated well provided the data necessary to analyze the well’s performance and to predict the long term reservoir behavior. Continuous chemical and radiochemical data were obtained to aid in analysis of well performance, explosive yield calculations, and surveillance for public health and safety assurances.Future activities at Project Rulison will concern the regulatory matters with respect to marketing of the gas.

Attenuation of blast waves by the atmosphere

Acoustic attenuation theory with coefficients obtained by experiment has been used to calculate losses from long range propagation along various paths in a standard atmosphere. Frequency dependence of attenuation has been incorporated into Fourier series approximations of positive phase waves from explosions to obtain net attenuations in terms of explosion yield and burst altitude. For some applications this incorporation improves on estimations from assumption of a single frequency of input. Attenuation results are presented for small 0.45-kg grenades burst at 30- to 90-km altitudes and for ton and kiloton explosives burst near the ground with waves propagated to 50-km altitudes and back to the ground near 200-km ranges.

Mercury tiltmeter as an infrasonic detector: Theory, observations, and applications

Observations of acoustic gravity waves at Eilat by a mercury tiltmeter are reported and interpreted. Waves belonging to the first gravity mode (GR0) and three acoustic modes (S0, S1, S2) that originated at the Chinese nuclear air blast of October 14, 1970, were simultaneously recorded on infrasonic microbarographs and the newly installed MIT (Massachusetts Institute of Technology) tiltmeters. The explosion (yield, about 5 Mt) produced at a distance of 5024 km a surface overpressure of about 300 μb at 240 sec. This overpressure in turn caused a horizontal displacement of 3 μ and a tilt of 3 × 10−10 rad at the same period. Plane-wave theory is used to show that the incident sound wave can excite a surface wave at the recording site through a second-order coupling effect. The induced waves propagate in the earth with the sound phase velocity and decay exponentially with depth. This theory is in good agreement with the observations. It is shown that the surface sound pressure and the induced ground motion are tied by a simple relation from which the mean rigidity of the upper crust at the recording site can be derived. The local rigidity of the granitic upper crust at Eilat is thus found to be 3.22 × 1011 dynes/cm2. Sensitivity of the tiltmeter to infrasonic waves in the period range 20–400 sec is estimated to be 10−12 rad/μb at zero site noise and electronic snr ratio of 1:1, with a detectability threshold at about 20 μb.

Regional dependence of surface-wave versus body-wave magnitudes

The observed regional dependence of surface-wave (Ms) versus body-wave (mb) magnitudes of underground explosions is due to differences in attenuation of body-waves beneath different source and station sites. The yield of an underground explosion is more easily and accurately estimated from Ms than from mb.

The nuclear explosive yields at Hiroshima and Nagasaki

The nuclear explosive yields at Hiroshima and Nagasaki have been calculated from measurements of the damage caused to some objects whose dynamical responses were simple enough to permit analysis. Examples include bent or snapped poles, squashed empty drums and cans, overturned memorial stones, some safe doors and the tops of office cabinets pushed in by the blast. The Hiroshima explosion was 12 ± 1 kilotons and the Nagasaki explosion was 22 ± 2 kilotons.

Magnitude versus yield of explosions

Magnitude versus yield of explosions