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Phase Screen Simulations of Seismic Wave Scattering Related to Monitoring Underground Nuclear Explosions

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Final rept. 23 Feb 1989-23 Apr 1991

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The objective of this project was to investigate seismic wave scattering effects, and to assess the existence and impact of mild nonlinear contributions to the attenuation of seismic signals, for purposes of monitoring underground nuclear explosions. We developed an efficient propagation algorithm, and applied it to the problems of understanding conversion of regional phases, coherence of waveforms measured by seismic arrays, and the accuracy of direct versus scattered phases. Experiments related to mild nonlinear attenuation were also reviewed. This final report consists of preprints of three papers which will be submitted for open publication. In the first paper, the accuracy and efficiency of the phase screen method for elastic waves are assessed by comparing with finite difference calculations of elastic wave propagation in 2-D random media. The phase screen method is a forward propagation algorithm which depends only on local S and P wave velocities. Both methods are used to generate synthetic seismograms for a suite of 2-D random media characterized by exponential and von Karman self-similar autocorrelation functions of varying strength and correlation length. In the second paper, phase screen simulations of vector wave propagation in elastic random media are applied to two studies relevant to monitoring underground nuclear explosions. Simulated coherence functions for vector waves are compared to analytic and simulated results also assume the Rytov approximation. In the third paper, experiments which reflect the attenuation of propagating pulses in salt in the moderate strain regime of . 001 to .000001, corresponding roughly to ranges of 100 to 10,000 meters from an explosion with yield of 1-kt, are reviewed.

Subject Categories:

  • Seismic Detection and Detectors
  • Nuclear Weapons

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