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Seismic Discrimination with Regional Phase Spectral Ratios: Investigation of Transportability
Final rept. 31 Jul 95-31 Jul 97
MAXWELL TECHNOLOGIES INC SAN DIEGO CA
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The Comprehensive Test Ban Treaty CTBT requires the location and identification of seismic events which might be associated with small potential underground nuclear explosion tests. For monitoring the CTBT at low magnitude thresholds, reliance must be placed on regional seismic measurements. Various regional discrimination techniques have been shown to be effective for identifying events in some areas, but the transportability of such methods into uncalibrated source areas remains a problem. This research developed procedures which could be useful for transporting regional phase spectral ratio discriminant measures by accounting for propagation path effects using prior knowledge of attenuation. We have found that by correcting for attenuation the scatter in Lg spectral ratio observations between stations could be reduced. However, these measurements still show considerable overlap between different source types which weakens the reliability of the discriminant. It might be possible to improve the reliability of regional phase spectral ratios by limiting effects of noise on the measurements by focusing on nearer stations, limiting the frequency band over which the ratios are formed.
APPROVED FOR PUBLIC RELEASE