Representing regional P/S discriminants for event indentification: a comparison of distance corrections, path parameter regressions, cap-averaging and kriging

Conference · Thu Jun 18 04:00:00 EDT 1998

OSTI ID:2462

Myers, S C ^[1]; Rodgers, A J; Schultz, C A; Walter, W R

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1. LLNL

Short-period regional P/S amplitude ratios hold much promise for discriminating low magnitude explosions from earthquakes in a Comprehensive Test Ban Treaty monitoring context. However, propagation effects lead to variability in regional phase amplitudes that if not accounted for can reduce or eliminate the ability of P/S ratios to discriminate the seismic source. lo this study, several representations of short-period regional P/S amplitude ratios are compared in order to determine which methodology best accounts for the effect of heterogeneous structure on P/S amplitudes. These methodologies are: I) distance corrections, including azimuthal subdivision of the data; 2) path specific crustal waveguide parameter regressions; 3) cap-averaging (running mean smoothing); and 4) kriging. The "predictability" of each method is established by cross-validation (leave-one-out) analysis. We apply these techniques to represent Pn/Lg, Pg/Lg and Pn/Sn observations in three frequency bands (0.75-6.0 Hz) at station ABKT (Alibek, Turkmenistan), site of a primary seismic station of the It~temational Monitoring System (IMS). Paths to ABKT sample diverse crustal stmctores (e.g. various topographic, sedimentary and geologic structures), leading to great variability in the observed P/S amplitude ratios. Subdivision of the data be back-azimuth leads to stronger distance trends than that for the entire data set. This observation alone indicates that path propagation effects due to laterally varying shucture are important for the P/S ratios recorded at ABKT. For these data to be useful for isolating source characteristics, the scatter needs to be reduced by accounting for the path effects and the resulting P/S ratio distribution needs to Gaussian for spatial interpolation and discrimination strategies to be most effective. Each method reduces the scatter of the P/S ratios with varying degrees of success, however kriging has the distinct advantages of providing the greatest variance reduction and a continuous correction surface with an estimate of the model uncertainty. The largest scatter reductions are obtained for the lowest frequency P/S ratios (< 3.0 Hz).

• Research Organization: Lawrence Livermore National Laboratory, Livermore, CA
• Sponsoring Organization: USDOE Office of Defense Programs (DP)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 2462
• Report Number(s): UCRL-JC-130739; ON: DE00002462
• Country of Publication: United States
• Language: English

Related Subjects

35 ARMS CONTROL
Data Analysis
Seismology
Verification