Use of P coda for determination of yield on nuclear explosions

Gupta, Indra N.; Blandford, R. R.; Wagner, Robert A.; Burnetti, J. A.; McElfresh, T.W.

doi:10.1111/j.1365-246x.1985.tb06502.x

Cited by 8 publications

(4 citation statements)

References 6 publications

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“…Since the later Lg coda is caused by scattering (Der et al 1984), the focusing/defocusing effect is expected to be greatly reduced by the averaging effect of the scattering process. A similar averaging effect on P coda has been extensively used to obtain more stable measurement of earthquakes and underground nuclear explosions (e.g., Ringdal 1983; Bullitt & Cormier 1984;Gupta et al 1985; Gupta & Blandford 1987;Baumgardt 1985a, b;Lay 1987;Lay & Welc 1987). Lg coda Q measurements, however, tend to be more subject to random errors due deviations of type (i) above, or by systematic errors caused by the assumption of an incorrect geometrical spreading term.…”

Section: Introductionmentioning

confidence: 99%

Attenuation of multiphase surface waves in the Basin and Range province, part I:LgandLgcoda

Xie¹,

Mitchell²

1990

Geophysical Journal International

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S U M M A R Y Broad-band data recorded by the Lawrence Livermore Laboratory Network are used to investigate whether or not Lg Q and Lg coda Q have similar values in the Basin and Range province of North America. In order to retrieve spectral estimates of the broad-band Lg and Lg coda signals, a hybrid method is used which retains high fidelity at lower frequencies while strongly smoothing the spectral estimates and minimizing the number of spectral points at high frequencies. A stochastic approach is used to model the Lg signal and ambient noise, and to analyse results from two-station determinations of Lg Q in the Basin and Range. The effects of ambient noise, frequency-dependent station site response and focusing/defocusing on Lg Q inversion are analysed. It is shown that after averaging spectral ratios determined from repeated observations over four two-station paths, a modest site effect will not cause significant errors in the resulting Lg Q relation. Using this inversion scheme and spectral ratio estimates averaged over those paths at frequencies between 0.2 and 2.5 Hz, we obtain the relation Q L g ( f ) = (267 f 56)f0.37*0.06 for the Basin and Range province. Further constraints on Lg Q were obtained from Lg coda, which, due to the natural averaging effect of scattering, is insensitive to effects of focusing/defocusing. To investigate the validity of the single isotropic scattering model for Lg coda in the Basin and Range province, we calculated ischrons for scatterers corresponding to later Lg coda signals, as required by the single scattering model. It is found that when significant portions of these isochrons are oceanic, Lg coda amplitude decay becomes irregular and abnormally slow, suggesting a strong scattering/reflection effect caused by the rapidly changing crustal structure along the coast. Applying the single isotropic scattering model to Lg coda records with isochrons mostly confined to the continental crust results in Q , ( f ) = (275 f 26) f 0.36*0.03 , which is nearly identical to our QLg relation. This indicates that even in a complicated geological province, a joint interpretation of the dynamic properties of Lg and Lg coda can be successful and fruitful. Inconsistent Lg Q and coda Q relations found in earlier studies in the Basin and Range province may be attributed to different settings of parameter trade-offs, different seismic phases, or different dynamic properties being used.

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Section: Introductionmentioning

confidence: 99%

Attenuation of multiphase surface waves in the Basin and Range province, part I:LgandLgcoda

Xie¹,

Mitchell²

1990

Geophysical Journal International

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“…noted that these Lg data do not exhibit the same degree of consistency as that of published P coda data[Gupta et al, 1985]• observed at a single teleseismic station, for the same events. The consistency of the data was determined by comparing with an my(P), estimated from ISC data[Marshall et al, 1984] using hundreds of stations Richards [1988].…”

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confidence: 50%

“…Richards [1988] has noted that teleseismic body waves do not re]ate reliably to yield unless data from many stations are combined. Richards [1988] noted that these Lg data do not exhibit the same degree of consistency as that of published P coda data [Gupta et al, 1985]• observed at a single teleseismic station, for the same events. In a study by Nuttl{[1986a], 22 Nevada Test Site (NTS) nuclear explosions in hard rock were analyzed.…”

Section: Fluctuations Of Direct Versus Scattered Phasesmentioning

confidence: 86%

Fluctuation analysis of elastic waves in random media via phase screen simulations

Fisk¹,

McCartor²

1993

J. Geophys. Res.

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Phase screen simulations of vector wave propagation in elastic random media are applied to two independent studies of seismic wave scattering. In the first study, transmission fluctuations are analyzed for incident P waves, propagated through a two‐dimensional version of the two‐layer model of Flatté and Wu (1988) of the crust and upper mantle beneath NORSAR. Numerically simulated coherence functions for vector elastic waves are compared to analytic and simulated results based on the parabolic approximation to the scalar wave equation. The usefulness of phase screen simulations for analyzing fluctuations for moderately strong scattering (∼ 2%–5% perturbations), and for three‐component data, is demonstrated. In the second study, effects of multi‐scale random structure on the variances of the initial P wave peak‐to‐peak amplitude and the rms amplitude of the transverse component in the velocity window between the average P and S wave speeds are investigated. A large number of synthetic seismograms are generated for eight random media models. This study shows that the relative variance of the rms scattered phase is far less dependent on the model than that of the direct phase. The variance of the forward scattered P wave depends greatly on the strength of the large‐scale heterogeneities.

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“…Several authors have examined the relative performance of magnitudes based on teleseismic P coda and direct P as relative size estimators, concluding that P coda generally yields more precise size estimates (BuLLITT and CORMIER,. 1984;BAUMGARDT, 1985;GUPTA et al, 1985;LAY and WELC, 1987).…”

Section: Introductionmentioning

confidence: 99%

Observations of teleseismicP wave coda for underground explosions

Lynnes

Lay

1988

PAGEOPH

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The early P wave coda (5-15 sec after the first arrival) of underground explosions at the Nevada Test Site is studied in the time domain using 2082 teleseismic short-period recordings, with the intent of identifying near-source contributions to the signals in the frequency range 0.2-2.0 Hz. Smaller magnitude events tend to have relatively high coda levels in the 0.4-0.8 Hz frequency band for both Yucca Flat and Pahute Mesa explosions. Coda complexity in this low-frequency passband is negatively correlated with burial depth for Pahute Mesa events but is only weakly correlated with depth for Yucca Flat events. Enhanced excitation of relatively long-period scattered waves for smaller, less deeply buried events is required to explain this behavior. Coda complexity in the 0.8-1.1 Hz band is positively correlated with magnitude and depth for Pahute Mesa events, but has no such dependence for Yucca Flat events. This may result from systematic variations between the spectra of direct signals and coda arrivals caused by pP interference for the largest events, all of which were detonated at Pahute Mesa. Another possible explanation is a frequency-dependent propagation effect on the direct signals of the larger events, most of which were located in the center of the mesa overlying strong lateral velocity gradients in the crust and upper mantle. Event average complexity varies spatially for both test sites, particularly in the 0.8 1.1 Hz band, providing evidence for frequency-dependent focussing or scattering by near-source structure. Both the direct arrivals and the early coda have strong azimuthal amplitude patterns that are produced by defocussing by mantle heterogeneity. The direct arrivals have stronger coherent azimuthal patterns than the early coda for Pahute Mesa events, indicating more pronounced deep crustal and shallow mantle defocussing for the direct signals. However, for Yucca Flat events the direct arrivals have less coherent azimuthal patterns than the coda, suggesting that a highly variable component of near-source scattering preferentially affecting the downgoing energy is superimposed on a pattern produced by mantle heterogeneity that affects the entire signal. This complicated behavior of the direct arrivals may be the result of triplications and caustics produced by the complex basement structure known to underlie the Yucca Flat test site. The presence of strong azimuthal patterns in the early coda indicates that source strength estimates based on early coda are subject to biases similar to those affecting estimates based on direct arrivals.

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Use of P coda for determination of yield on nuclear explosions

Cited by 8 publications

References 6 publications

Attenuation of multiphase surface waves in the Basin and Range province, part I:LgandLgcoda

Attenuation of multiphase surface waves in the Basin and Range province, part I:LgandLgcoda

Fluctuation analysis of elastic waves in random media via phase screen simulations

Observations of teleseismicP wave coda for underground explosions

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