LLNL's Regional Model Calibration and Body-Wave Discrimination Research in the Former Soviet Union using Peaceful Nuclear Explosions (PNEs)
Long-range seismic profiles from Peaceful Nuclear Explosions (PNE) in the Former Soviet Union (FSU) provide a unique data set to investigate several important issues in regional Comprehensive Nuclear-Test-Ban Treaty (CTBT) monitoring. The recording station spacing ({approx}15 km) allows for extremely dense sampling of the propagation from the source to {approx} 3300 km. This allows us to analyze the waveforms at local, near- and far-regional and teleseismic distances. These data are used to: (1) study the evolution of regional phases and phase amplitude ratios along the profile; (2) infer one-dimensional velocity structure along the profile; and (3) evaluate the spatial correlation of regional and teleseismic travel times and regional phase amplitude ratios. We analyzed waveform data from four PNE's (m{sub b} = 5.1-5.6) recorded along profile KRATON, which is an east-west trending profile located in northern Sibertil. Short-period regional discriminants, such as P/S amplitude ratios, will be essential for seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) at small magnitudes (m{sub b} < 4.0). However, P/S amplitude ratios in the short-period band, 0.5-5.0 Hz, show some scatter. This scatter is primarily due to propagation and site effects, which arise from variability in the elastic and anelastic structure of the crustal waveguide. Preliminary results show that Pg and Lg propagate efficiently in north Siberia at regional distances. The amplitude ratios show some variability between adjacent stations that are modeled by simple distance trends. The effect of topography, sediment and crustal thickness, and upper mantle discontinuities on these ratios, after removal of the distance trends, will be investigated. The travel times of the body wave phases recorded on KEATON have been used to compute the one-dimensional structure of the crust and upper mantle in this region. The path-averaged one-dimensional velocity model was computed by minimizing the first arriving P-phase travel-time residuals for all distances ({Delta} = 300-2300 km). A grid search approach was used in the minimization. The most significant features of this model are the negative lid-gradient and a low-velocity zone in the upper mantle between the depths of 100-200 km; precise location of the LVZ is poorly constrained by the travel time data. We will extend our investigation to additional PNE lines to further investigate the amplitude and travel-time variations in eastern and central Eurasia. Finally, the dense station spacing of the PNE profiles allows us to model the spatial correlation of travel times and amplitude ratios through variogram modeling. The statistical analysis suggests that the correlation lengths of the travel-time and amplitude measurements are 12{sup o} and 10{sup o}, respectively.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 791760
- Report Number(s):
- UCRL-JC-138991; TRN: US0300685
- Resource Relation:
- Conference: 22nd Annual Department of Defense/Department of Energy Seismic Research Symposium, New Orleans, LA (US), 09/12/2000--09/15/2000; Other Information: PBD: 14 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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