Assessment of Regional Explosion Discriminants Using Data Sets of Unparalleled Spatial Sampling

Abstract

Abstract : We used data from the Bighorn Arch Seismic Experiment (BASE) to determine P-wave velocity structure and assess regional explosion discriminants in north-central Wyoming. BASE is a multi-scale, hybrid active/passive seismic experiment designed to determine crust and mantle structure below the Bighorn Mountains. North-central Wyoming experiences a spectrum of manmade and natural events, from regional earthquakes and teleseisms to mine blasts and single fire shots, making the region a compelling natural laboratory in which to investigate implications for regional discrimination. The velocity structure across the region is calculated through tomographic inversion of arrival times from 21 controlled-source single-fired seismic shots. The detailed velocity models can also be used to investigate the degree of spatial sampling of the seismic wavefield needed to characterize 3D wave propagation effects. For the discrimination study, we used the single-charge explosions from the BASE experiment, mining explosions, and approx. 40 earthquakes to test seismic discriminants using USARRAY broadband data and data recorded at station RSSD. An amplitude ratio of Pg (6-12 Hz) versus Lg (6-12 Hz) mostly separated the earthquakes from the explosions. Lg spectral ratios also separated the explosions from the earthquakes, but not as well as the Pg/Lg ratio.