1742 Bulletin of the Seismological Society of America, Vol. 96, No. 5, pp. 1742–1752, October 2006, doi: 10.1785/0120050178 M s :m b Discrimination Study of Mining Explosions in Wyoming, USA, and in QianAn, China by Rong-Mao Zhou, Brian W. Stump, and Christopher T. Hayward 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 earth- quakes 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 simulta- neously 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. Introduction and Motivation Large-scale chemical blasts are routinely conducted by the mining industry to remove overburden or to fragment rocks. Large mining explosions are conducted with delays between individual charges in an array, resulting in source durations as great as several seconds. The total size of the explosion, its time duration, horizontal and vertical spall force components from material casting, and spatial char- acteristics can generate short- to intermediate-period (1–20 sec) surface waves (Hedlin et al., 2002; Zhou et al., 2003a; Zhou and Stump, 2004). Analysis of surface-wave disper- sion from this event type provides a method for determining the shallow crustal shear-wave velocity. Because regional networks often record many mining explosions, the relative excitation of regional body and surface waves may be useful in identifying some of these mining events. Characterization of propagation path effects provides for further study of source-induced differences in the re- gional waveforms. Data from blasts in Wyoming and north- east China are used to study the generation of regional seis- mic signals from mining explosions. We focus on both the body waves and intermediate-period surface waves from these sources. A physical understanding of mining explosions as sources of regional seismic waves would provide a basis for the development of seismic discriminants for these source types. The existence of regional body waves and intermediate- period surface waves from these sources suggests that a modification of the successful M s :m b teleseismic discrimi- nant (Stevens and Day, 1985) might be worth exploring. Marshall and Basham (1972) suggested that M s esti- mation could be extended to smaller events and shorter pe- riods. It is recognized that regional observations hold the key to better monitoring at low magnitudes. As a result, there is high interest in extending M s :m b analysis to regional data (Patton, 2001; Bonner et al., 2003). Characterization of short-period propagation path effects on regional surface waves will be critical to such applications. To understand the applicability of this discriminant, the relative surface- wave excitation difference between contained, possibly nu- clear, single-fired explosions and delay-fired mining explo- sions must also be assessed (Myers et al., 1999). The data