Ms:mb Discrimination Study of Mining Explosions in Wyoming, USA, and in QianAn, China

Abstract

We investigate the use of intermediate-period surface-wave magnitude, M s , and high-frequency body-wave magnitude, m b , from regional mining explosions for event discrimination by using techniques originally intended for separating earthquakes from explosions with teleseismic observations. The actual values of M s and m b suggest that the surface waves generated by long-duration mining explosions can make them appear earthquakelike. The data from the single anomalous shot indicate that if a significant part of the total explosives is simultaneously detonated the event will move into the explosion population. Data for this study are taken from a portable broadband deployment in Wyoming recording mining explosions in the Powder River Basin and a broadband network currently deployed in northeast China. The magnitudes, M s (vmax) and m b were estimated for five, kiloton-size mining explosions, four in Wyoming and one in QianAn, China. The resulting network M s : m b data were compared with data from a previous study that included earthquakes and contained single-fired explosions (Stevens and Day, 1985; Bonner et al. , 2003). Although the previous studies mostly examined events larger than those in this study, the Wyoming and China mining events plot in the earthquake population. Data from the anomalous Wyoming event, a blast in which a failure of the timing system caused a large portion of the blast pattern to simultaneously detonate, plot in the explosion population with m b 4.4. The simultaneous detonation of a large portion of blast array increased the body-wave magnitude but had little effect on surface-wave magnitude.