Seismic source functions for explosions in a non-spherical cavity embedded in a scattering environment: application to the regional discrimination of nuclear explosions and earthquakes

Ben‐Menahem, Ari

doi:10.1111/j.1365-246x.1997.tb04074.x

Cited by 5 publications

(5 citation statements)

References 25 publications

(23 reference statements)

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“…The second factor that contributes to nonisotropic seismic radiation pattern from explosive sources is the shape of the explosion cavity, and the location of explosive source in that cavity (Rial, and Moran, 1986;Stevens et al, 1991;Zhao and Harkrider, 1992;Ben-Menahem and Mikhailov, 1995;Gibson et al, 1996;Ben-Menahem, 1997;lrnhof and Toks6z, 2002;). The contribution of this mechanism to nonisotropic radiation depends on the aspect ratio of the cavity (i.e., ratio of length to diameter), and placement of the source within the cavity (Gibson et al, 1996).…”

Section: Objectives Of This Researchmentioning

confidence: 99%

“…The third mechanism contributing to complex seismic radiation from an explosion is the near source scattering (Gupta et al, 1990;Johnson, 1997;Ben-Menahem, 1997;Imhof and Toks6z, 2002, 002). This mechanism, not studied as extensively, could be significant when strong scatterers are present near the source.…”

Section: Objectives Of This Researchmentioning

confidence: 99%

“…The scatterers act as secondary sources with difference radiation patterns and different distance dependencies than the primary waves. A large amount of S wave energy can be generated by this mechanism by an explosion (Leavy, 1993;Ben-Menahem, 1997;Inhof andToks6z, 2000, 2002). Toks6z (2000, 2002) modeled the effects of scattering from cylindrical cavities near a shot using a multiple-multipole approximation.…”

Section: Effect Of Near Source Scattering On Seismic Waves From Explomentioning

confidence: 99%

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Characterization of an Explosion Source in a Complex Medium by Modeling and Wavelet Domain Inversion

Toksoez¹

2006

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Section: Objectives Of This Researchmentioning

confidence: 99%

Section: Objectives Of This Researchmentioning

confidence: 99%

Section: Effect Of Near Source Scattering On Seismic Waves From Explomentioning

confidence: 99%

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Characterization of an Explosion Source in a Complex Medium by Modeling and Wavelet Domain Inversion

Toksoez¹

2006

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“…We also ignore stress-induced anisotropy. E¡ects of scattering due to stress-induced inhomogeneities were discussed in an earlier paper (Ben-Menahem 1997).…”

Section: Introductionmentioning

confidence: 98%

Effect of a non-linear boundary layer on the radiation from earthquakes and underground nuclear explosions

Ben‐Menahem

1998

Geophys. J. Int.

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A constitutive equation in the immediate source region is postulated. It is proposed that between the permanently deformed source volume and the linear zone there exists a microfractured boundary layer having the constitution of a five‐parameter Murnaghan solid that exhibits both geometrical finite strain and physical cubic terms in the energy density function. Waves excited by the source carry the signature of the boundary layer into the linear zone, all the way to the far field. The mathematical realization of this programme consists of the application of the longwave Born–Rayleigh approximation to the Landau–Goldberg equation. The perturbed field, governed by an additional force system, is represented as a multipole expansion of eigenvector spherical harmonics of the unperturbed background field. Our solution aims at the spatial characteristics of the 3‐D perturbed field (e.g. radiation patterns, amplitude amplification, etc.) together with its frequency‐content features. The results show, in general, that for every spatial mode with indices (ℓ1, m1) fed into the non‐linear boundary layer system, there emerges in the elastic zone the output modes (ℓ1±2s, 2m1), s=0,2,4,…. Compressional and shear modes generate each other (‘mode crossing’), and spatial field harmonics of lower and higher orders than originally existed in the primary field appear. In addition, one encounters the expected frequency doubling in the spectral displacements of the first‐order perturbation. Detailed calculations are made, especially for dipolar sources, which include explosion (ℓ1=0,m1=0) and shear dislocations (ℓ1=2, m1=0,1,2). It is revealed that the boundary layer tends to amplify the source field by a factor that may reach 4 for explosions in pre‐existing cavities and 2 for earthquakes. Hence, the amplification will effectively limit the true seismic decoupling of underground nuclear explosions to a limiting value of under 70 and tend to boost the true seismic moments of earthquakes. In the latter case the non‐linear theory suggests the introduction of two new source parameters: a virtual radius, r0, associated with the yield limit of rocks, and a larger radius associated with the elastic limit of rocks. It is shown that for shear dislocations, the fault's area is interpreted geometrically as a virtual spherical surface of radius r0. As long as small finite strains are assumed inside a thin boundary layer, scrambling of the wavefield (that is displacement amplification, generation of higher‐degree multipoles and mode crossing) is the most conspicious physical perturbation, independent of any non‐classical modification of the constitutive law. In this sense, the salient gross features of our final results are model‐independent. Our results serve as a bridge between the microscopic and macroscopic theories of fracture and hopefully pave the road towards a dynamical theory of earthquake‐source mechanisms.

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“…In this article, we focus on another process which has been little studied and involves the elastic interactions between an explosive source and the elastic heterogeneities located in the near field [ Oliver et al , ; Smith , ; McLaughlin et al , ], at relatively lower frequencies. The isotropic symmetry of the radiation pattern of the explosion, as well as the compressional mode of radiation, can be broken due to small‐scales inhomogeneities in the immediate vicinity of the source [ Leavy , ; Ben‐Menahem , ], which is different and complementary to the study of the scattering everywhere but at the source [ Frankel and Clayton , ]. Recently, some numerical approaches investigated the case of explosions with near‐source heterogeneities and found significant shear waves generation but at higher frequencies [ Pitarka et al , ; Stevens and Xu , ].…”

Section: Introduction and Motivationsmentioning

confidence: 99%

Homogenized moment tensor and the effect of near‐field heterogeneities on nonisotropic radiation in nuclear explosion

2016

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We investigate the effect of small‐scale heterogeneities close to a seismic explosive source, at intermediate periods (20–50 s), with an emphasis on the resulting nonisotropic far‐field radiation. First, using a direct numerical approach, we show that small‐scale elastic heterogeneities located in the near‐field of an explosive source, generate unexpected phases (i.e., long period S waves). We then demonstrate that the nonperiodic homogenization theory applied to 2‐D and 3‐D elastic models, with various pattern of small‐scale heterogeneities near the source, leads to accurate waveforms at a reduced computational cost compared to direct modeling. Further, it gives an interpretation of how nearby small‐scale features interact with the source at low frequencies, through an explicit correction to the seismic moment tensor. In 2‐D simulations, we find a deviatoric contribution to the moment tensor, as high as 21% for near‐source heterogeneities showing a 25% contrast of elastic values (relative to a homogeneous background medium). In 3‐D this nonisotropic contribution reaches 27%. Second, we analyze intermediate‐periods regional seismic waveforms associated with some underground nuclear explosions conducted at the Nevada National Security Site and invert for the full moment tensor, in order to quantify the relative contribution of the isotropic and deviatoric components of the tensor. The average value of the deviatoric part is about 35%. We conclude that the interactions between an explosive source and small‐scale local heterogeneities of moderate amplitude may lead to a deviatoric contribution to the seismic moment, close to what is observed using regional data from nuclear test explosions.

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Seismic source functions for explosions in a non-spherical cavity embedded in a scattering environment: application to the regional discrimination of nuclear explosions and earthquakes

Cited by 5 publications

References 25 publications

Characterization of an Explosion Source in a Complex Medium by Modeling and Wavelet Domain Inversion

Characterization of an Explosion Source in a Complex Medium by Modeling and Wavelet Domain Inversion

Effect of a non-linear boundary layer on the radiation from earthquakes and underground nuclear explosions

Homogenized moment tensor and the effect of near‐field heterogeneities on nonisotropic radiation in nuclear explosion

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