Refinement of Regional Distance Seismic Moment Tensor and Uncertainty Analysis for Source-Type Identification
CALIFORNIA UNIV BERKELEY BERKELEY SEISMOLOGICAL LAB
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We build on our earlier results DE-FC52-06NA27324, Dreger et al., 2008 Ford et al., 2010 Ford et al., 2009a, b Ford et al., 2008 in which it has been demonstrated that regional distance moment tensor analysis can discriminate explosions from naturally occurring earthquakes and mine collapses. In this project, as an effort to refine procedures for implementation we develop a more complete understanding of uncertainties, and define robust methods for their characterization. In Ford et al., 2008, it was found that populations of explosions, earthquakes and collapses in the Western U.S. separated on a Hudson et al. 1989 diagram enabling source-type discrimination. A question the current research addresses is whether these populations remain separated for other regions of the world. We have compiled a database of naturally occurring, and induced seismicity to examine the distribution of non-double-couple seismic moment tensors in a Hudson source-type diagram to be used as an a priori constraint. The results indicate the region of tradeoff between a pure explosion monopole and a compressional major vector dipole CLVD is relatively devoid of natural and induced seismicity, which is favorable for seismic moment tensor source-type discrimination. In addition, we present new results for the North Korean test combining regional and teleseismic observations to further restrict tradeoff between pure explosion and pure CLVD solutions for nuclear explosions. We are investigating the velocity model dependence of vanishing free-surface traction effects on seismic moment tensor inversion of shallow sources, and are working on developing a damped inversion to suppress these effects and reduce bias in scalar moment estimates for shallow sources. Finally, we are working toward extending the regional seismic moment tensor database for nuclear explosions and natural seismicity for the Korean Peninsula and Kazakhstan.