Regional seismic discrimination research at LLNL

The ability to verify a Comprehensive Test Ban Treaty (CTBT) depends in part on the ability to seismically detect and discriminate between potential clandestine underground nuclear tests and other seismic sources, including earthquakes and mining activities. Regional techniques are necessary to push detection and discrimination levels down to small magnitudes, but existing methods of event discrimination are mainly empirical and show much variability from region to region. The goals of Lawrence Livermore National Laboratory`s (LLNL`s) regional discriminant research are to evaluate the most promising discriminants, improve the understanding of their physical basis and use this information to develop new and more effective discriminants that can be transported to new regions of high monitoring interest. In this report the authors discuss preliminary efforts to geophysically characterize the Middle East and North Africa. They show that the remarkable stability of coda allows one to develop physically based, stable single station magnitude scales in new regions. They then discuss progress to date on evaluating and improving physical understanding and ability to model regional discriminants, focusing on the comprehensive NTS dataset. The authors apply this modeling ability to develop improved discriminants including slopes of P to S ratios. They find combining disparate discriminant techniques is particularly effective in identifying consistent outliers such as shallow earthquakes and mine seismicity. Finally they discuss development and use of new coda and waveform modeling tools to investigate special events