Seismic Attenuation, Event Discrimination, Magnitude and Yield Estimation, and Capability Analysis
LAWRENCE LIVERMORE NATIONAL LAB CA
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We present the latest results on Lawrence Livermore National Laboratorys calibration efforts for seismic attenuation of regional body and surface waves that have application to many different areas of nuclear explosion monitoring. We have developed methods that use amplitude measurements of the direct regional phases Pn, Pg, Sn Lg to determine the attenuation structure of the lithosphere in Eurasia. The amplitudes are inverted simultaneously for attenuation parameters Qp, Qs of the crust and upper mantle, along with event source terms and station site terms. We are applying similar methodologies to coda amplitudes. Like direct waves, coda waves are subject to path-dependent variations in amplitudes. We see geographic similarities between the crustal shear-wave attenuation and the results from the coda attenuation. Calibration of coda in the Middle East and other areas is complicated by the fact that the dominant S-wave phase is either Sn or Lg depending on tectonic region, distance, and frequency. Over the past year, we have made great progress on the calibration of surface wave attenuation with the development of the Surface Wave Amplitude Processor SWAP. With this tool, we are able to make surface wave amplitude measurements quickly, reliably, and consistently. We will be presenting a preliminary surface wave attenuation tomography of the Middle East. Regional attenuation models are directly applicable to event discrimination, such as high-frequency regional PS discriminants e.g., PnLg, PgLg, PnSn and longer period Msmb. Correcting the observed amplitudes for path-dependent variations reduces scatter in the earthquake population and increases separation from explosions. Better body-wave path corrections might even allow the extension of PS discrimination to lower frequencies so long as true source differences between events exist at those frequencies.
- Geology, Geochemistry and Mineralogy