Regional discrimination of NTS (Nevada Test Site) explosions and western US earthquakes: Multivariate discriminants

Technical Report · Sat Nov 01 04:00:00 EST 1986

OSTI ID:7026704

Glaser, R E; Taylor, S R; Denny, M D; Vergino, E S

Twelve of the earthquake/explosions discriminants outlined in Pomeroy et al. (1982) are evaluated in the western US (WUS). The data consist of 330 NTS explosions and 130 WUS earthquakes in the magnitude range of 2.5 to 6.5 recorded at four broadband seismic stations operated by Lawrence Livermore National Laboratory (LLNL). The stations surround NTS at distances of about 200 to 400 km. The propagation paths for the earthquakes range from approximately 175 to 1300 km and are confined mainly to the Basin and Range. The discriminants tested include m/sub b/ : M/sub s/, relative excitation of short-period SH waves, P/sub n/, P/sub g/, P/sub max/, and L/sub g/ amplitude ratios generation of higher mode surface waves, long period (LP) surface wave energy density, L/sub g/ / R/sub g/ amplitude ratio, excitation of Sn/sub n/, spectral ratios in P/sub n/, P/sub g/ and L/sub g/, third moment of frequency, spectral ratio of LP Love to Rayleigh waves, and Thirlaways's depth discriminant. A multivariate discrimination technique is described that is designed to handle missing data while providing optimum classification of an unknown event based on a given set of discrimination variables. The discrimination variables are first transformed to be insensitive to magnitude, path, or features of the test program. Tests show that the commonly used assumption of equal covariance matrices for the earthquake and explosion populations (resulting in a linear discrimination function) is not valid. However, a quadratic discrimination function is appropriate. An optimality criterion, misclassification cost minimization, is used to select the best set of discrimination variables at each station. Application of the multivariate technique to individual stations shows misclassification rates ranging from 4 to 20% and 4 to 27% for explosions and earthquakes, respectively.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7026704
• Report Number(s): UCID-20930; ON: DE87003602
• Country of Publication: United States
• Language: English

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