Regional Magnitude Research Supporting Broad-Area Monitoring of Small Seismic Events

Abstract : The Los Alamos National Laboratory's Ground-Based Nuclear Explosion Monitoring Research and Engineering (GNEMRE) Program has a long-standing magnitude research project in support of regional yield estimation and source discrimination. This project has developed magnitude-yield scaling relationships based on regional P, S phases and coda waves to improve our capabilities to monitor nuclear explosions over broad areas and at low yields. Due to the great variability of regional seismograms, the methods developed for broad-area monitoring must be adaptable to different phases and frequency bands. These requirements, along with an understanding of the transportability of scaling relationships, pose a significant challenge from both practical and theoretical standpoints since any broad-area method needs a sound physical basis to be ultimately successful. Coda wave efforts have recently focused on practical aspects such as schema design for the exchange of calibration parameters and details of signal processing coding to match measurements between institutions, as well as advanced aspects of extending near-regional coda techniques to broad area and far-regional distances. We have developed the MagYield 0.10 schema, which ties to National Nuclear Security Administration (NNSA) Knowledge Base (KB) core schema for the exchange of envelope recipes, coda calibration parameters, and yield regression parameters. Exacting tests of signal processing methods between institutions uncovered issues with a widely used deconvolution code and code-dependent effects of non-ideal bandwidth/Nyquist ratios. Extension of the coda method to broad area far-regional distances showed the importance of 2-D path effects, as well as 2-D phase type (P vs. Sn vs. Lg coda) and 2-D transfer function effects.

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