Seismic-source representation for spall
Spall may be a significant secondary source of seismic waves from underground explosions. The proper representation of spall as a seismic source is important for forward and inverse modeling of explosions for yield estimation and discrimination studies. We present a new derivation of a widely used point force representation for spall, which is based on a horizontal tension crack model. The derivation clarifies the relationship between point force and moment tensor representations of the tension crack. For wavelengths long compared with spall depth, the two representations are equivalent, and the moment tensor time history is proportional to the doubly integrated time history of the point force. Numerical experiments verify that, for regional seismic phases, this equivalence is valid for all frequencies for which the point-source (long wavelength) approximation is valid. Further analysis shows that the moment tensor and point force representations retain their validity for non-planar spall surfaces, provided that the average dip of the surface is small. The equivalency of the two representations implies that a singular inverse problem will result from attempts to infer simultaneously the spectra of both these source terms from seismic waveforms. If the spall moment tensor alone is estimated by inversion of waveform data, the inferred numerical values of its components will depend inversely upon the source depth which is assumed in the inversion formalism.
- Research Organization:
- Scripps Institution of Oceanography, La Jolla, CA (United States)
- OSTI ID:
- 5117972
- Report Number(s):
- AD-A-239064/9/XAB; CNN: F19628-88-K-0039
- Country of Publication:
- United States
- Language:
- English
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58 GEOSCIENCES
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98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
ARMS CONTROL
CRACKS
DEPTH
DETECTION
DIMENSIONS
EXPLOSIONS
FRAGMENTATION
MATHEMATICAL MODELS
MECHANICS
NUCLEAR EXPLOSION DETECTION
NUCLEAR EXPLOSIONS
NUCLEAR REACTIONS
NUCLEAR WEAPONS
ROCK MECHANICS
SEISMIC DETECTION
SEISMIC WAVES
SEISMOLOGY
SPALLATION
SURFACES
TENSORS
TESTING
UNDERGROUND EXPLOSIONS
VERIFICATION
WAVE FORMS
WEAPONS
YIELDS