Observations of Love Waves from the HUMBLE REDWOOD Explosions with Implications for P/S Ratios at Local Distances
WESTON GEOPHYSICAL CORP LEXINGTON MA
Pagination or Media Count:
The ratio of 6-8 Hz PS energy is a robust discriminant between earthquakes and explosions at regional distances e.g., Taylor et al., 1989 Walter et al., 1995 Hartse et al., 1997 Pasyanos et al., 2009. We have examined the PS discriminant at regional and local distances for simultaneously-detonated chemical explosions conducted for the Non-Proliferation Experiment NPE, Source Phenomenology Experiments in Arizona SPE Black Mesa and Morenci, Alaska Frozen Rock Experiments FRE Frozen and Unfrozen and the New England Damage Experiment NEDE. These shots were conducted at various scaled depths of burial in lithology ranging from granite to alluvium. Several of these datasets have delay-fired mining explosions detonated in close proximity to the dedicated shots for comparison. During the past year, we have added additional datasets to our analysis of PS ratios from explosions HUMBLE REDWOOD HR I and II. The HR I and II experiments Foxall et al., 2008,2010 provide a unique opportunity to study local phase generation, in particular S-waves, from above- and below-ground explosions. We have identified P-waves higher and fundamental-mode Rayleigh Rg waves, and Love specifically SH, the horizontally polarized shear wave waves from 656 kg ANFO explosions detonated above and in alluvium in the Albuquerque Basin, New Mexico. Identification of P and Rg was relatively simple based on arrival times and rectilinear and retrograde elliptical particle motion, respectively. Identification of higher mode Rayleigh waves required particle motion prograde elliptical and synthetic modeling. The candidate SH arrivals from the above-ground shots are difficult to positively identify as Love waves due to small amplitudes and complex particle motion.