Use of large cavities to reduce seismic waves from underground explosions

Herbst, Roland F.; Werth, G.C.; Springer, Donald L.

doi:10.1029/jz066i003p00959

Cited by 38 publications

(17 citation statements)

References 14 publications

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“…This means that the yield as determined by the growth of the shock front (effective yield) will be less than that of a tamped (zero radius cavity) explosion of the same detonation energy. Theoretical studies [Latter et al, 1961b] and a nuclear experiment [Herbst et al, 1961] indicate that at 1 Hz a seismic signal decoupling factor in the range of between 70 and 200 can be achieved, raising the possibility of the evasion of a treaty which might ban or place a threshold limit on nuclear testing. Very large cavities (•20 m Copyright 1989 by the American Geophysical Union.…”

Section: Introductionmentioning

confidence: 99%

The effective yield of a nuclear explosion in a small cavity in geologic material: Enhanced coupling revisited

King¹,

Freeman²,

Eilers³

et al. 1989

J. Geophys. Res.

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The hydrodynamic yield of an underground nuclear explosion in a small cavity has been recalculated using computer modeling. We have considered explosions in spherical cavities having scaled radii, R/W1/3, less than 3.5 m/kt1/3 (R is the cavity radius in meters and W is the explosion energy in kilotons) in quartz (SiO2) using an available equation of state (Ree, 1976). These calculations show, at a scaled radius of ≈1.5 m/kt1/3, a maximum hydrodynamic yield substantially greater than that of an explosion in a tamped cavity (enhanced coupling) as measured by the shock time of arrival in the near field. These results are in qualitative agreement with those of earlier investigators who utilized the reduced displacement potential to evaluate coupling. We found, however, that the coupling coefficient (ratio of yield for cavity model to yield for tamped model) is significantly reduced when an improved quartz equation of state is employed. We also calculated enhanced coupling in two additional geologic materials, salt and tuff. All of the calculations mentioned above (including our initial ones) were simplified through the omission of significant thermal radiation contributions to energy and pressure in the cavity and the diffusion by photon transport of energy from the explosion cavity into the adjacent rock. When we take these processes into account, we find that for a cavity radius of approximately 1.5 m/kt1/3, near the peak of enhancement for our models with no radiation, there is instead a decoupling of about 15% in SiO2, 20% in tuff, and about 15% in salt. At the largest scaled cavity radius considered, 3.42 m/kt1/3, there is a decoupling of 40% in SiO2, 35% in tuff, and 35% in salt. For all three media the coupling coefficients decrease monotonically as the cavity radius increases. This result is different from previous ones in which the radiation terms were neglected. The radiation processes not only provide another method for vaporization of the rock but also change the effective gamma of the cavity gas as a result of the reduced cavity temperature and the addition of radiation pressure and energy terms. We have also found that the major effect on coupling is due to the contribution of radiation to the equation of state. Computer calculations which omitted radiation diffusion showed that the major change in effective coupling is due to the radiation energy and pressure modifications of the equation of state and to the corresponding changes in the effective gamma of the cavity gas. Thus, while the radiation diffusion is responsible for minor changes in the coupling curves, the main trend of these curves does not depend on diffusion.

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Section: Introductionmentioning

confidence: 99%

The effective yield of a nuclear explosion in a small cavity in geologic material: Enhanced coupling revisited

King¹,

Freeman²,

Eilers³

et al. 1989

J. Geophys. Res.

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“…It is well known that the teleseismic amplitude resulting from an undergound explosion can be reduced by up t o two orders of magnitude by performing the explosion in a large, preexcavated cavity (Latter et al 1961;Herbst, Werth & Springer 1961: Springer etal. 1968).…”

Section: Introductionmentioning

confidence: 99%

Blast wave effects on decoupling with axisymmetric cavities

Glenn

Rial

1987

Geophys J Int

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An expiosion is considered in an initially air-filled, underground spherical cavity t o which is connected a long, cylindrical tunnel. The cavity and tunnel size are, taken together, equivalent in volume t o a fully decoupled spherical cavity (in accordance with the Latter criterion). Calculations indicate that, when the air is at standard conditions, the shock speed in the tunnel, D , is of the same order as the sound speed in the surrounding rock medium, c L . Moreover, the blast wave is approximately quasi-steady, and can be represented by a simple analytical function. This in turn permits a closed form solution for the far-field seismic amplitude spectrum. It is found that the low-pass filtering effectiveness of the tunnel is largely diminished unless D/cL s 1. With air-filled cavities, and depending on the source-receiver orientation, the spectral amplitude can actually exceed significantly the equivalent volume-sphere result. For practical purposes, this means that unless the cavity and tunnel are initially evacuated, say with a steam ejector system, the high-frequency decoupling capability will be no better, and possibly worse, than a conventional spherical cavity of the same total volume.

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“…The pressure step function was used by Latter et al [1961a] in developing their cavitydecoupling theory. Herbst et al [1961] found that the cavity-pressure histories for the Cowboy series of chemical explosions are approximated by a step function plus an impulse function. Patterson [1966] showed that a cavity-pressure step function is a good approximation for nuclear explosions in cavities.…”

Section: The Explosion Modelmentioning

confidence: 99%

An energy approach to seismic coupling analysis

Rodean¹

1972

J. Geophys. Res.

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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.

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Use of large cavities to reduce seismic waves from underground explosions

Cited by 38 publications

References 14 publications

The effective yield of a nuclear explosion in a small cavity in geologic material: Enhanced coupling revisited

The effective yield of a nuclear explosion in a small cavity in geologic material: Enhanced coupling revisited

Blast wave effects on decoupling with axisymmetric cavities

An energy approach to seismic coupling analysis

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