Abstract

Chemical blasts from quarrying operations in central Texas are routinely recorded by the W. M. Keck Foundation Seismological Observatory near China Spring, Texas. The Keck Observatory consists of a single, broadband, three-component, borehole seismograph system. Five quarries, located at distances ranging from 16 to 101 km from the observatory, each detonate from 1 to 6 tons of ammonium nitrate/fuel oil explosive on the average of twice per week. For every quarry for which the orientation of the working face could be determined, dispersed Rg waves are recorded at the Keck Observatory from those quarries at which the working face is directed away from the observatory, but are not observed or are severely attenuated from those quarries at which the working face is directed toward the observatory. Seismograms containing the dispersed Rg are easily recognized as quarry blasts, but those in which the dispersed Rg is absent look like small earthquakes.

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