Accession Number:

ADA516009

Title:

Predicting Explosion-Generated SN and LG Coda Using Syntheic Seismograms

Descriptive Note:

Conference paper

Corporate Author:

WESTON GEOPHYSICAL CORP LEXINGTON MA

Personal Author(s):

Report Date:

2008-09-01

Pagination or Media Count:

11.0

Abstract:

Recent examinations of the characteristics of coda-derived S and Lg spectra for yield estimation have shown that the spectral peak of Nevada Test Site NTS explosion spectra is depth-of-burial dependent, and that this peak is shifted to higher frequencies for Lop Nor explosions at the same depths. To confidently use coda-based yield formulas, we need to understand and predict coda spectral shape variations with depth, source media, velocity structure, topography, and geological heterogeneity. We are in the final year of a synthetic seismogram study to evaluate the characteristics of Lg coda generated from explosions and earthquakes. To meet our objectives, we have developed a deterministic model for the western United States and the NTS. In order to generate coda in our 2D and 3D pseudospectral simulations, heterogeneity was added in the crust andor upper mantle. Three parameterscorrelation length, Hurst number H, and fractional velocity perturbation of the heterogeneities-are used to construct different realizations of random media. We have estimated the heterogeneity parameters for the NTS using available seismic and geologic data. Lateral correlation, variance and coherence measures between seismic traces are estimated from clusters of nuclear explosions and well-log data. The horizontal von Karman correlation length estimated for nuclear explosion Lg phases is between 0.4-1.1 km, with Hurst numbers between 0.3 and 0.6. A dominant heterogeneity dimension of 0.5-1.8 km results in best Lg coda coherence at frequencies between 1 and 4 Hz.

Descriptors:

Subject Categories:

  • Seismology
  • Explosions

Distribution Statement:

APPROVED FOR PUBLIC RELEASE


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