Near-source and Regional Experiments to Quantify Coupling and Propagation Effects of Seismic and Infrasound Signals from Mining Explosions
Abstract
Mining explosions designed to fragment rock are known to be regular sources of seismic waves as exemplified by the routine identification of these events in the USGS Mining Seismicity Report. Near-surface explosions can also generate low frequency acoustic waves or infrasound that can propagate through the atmosphere to regional distances. An understanding of source contributions to the size and character of waves initiated in the solid earth and atmosphere can be used to interpret propagation path effects as well as provide a physical understanding of characteristics that can be used for identifying the source type from the regional observations. The porphyry copper district of the SW United States was chosen for the study of these effects because of the existence of mining explosions that are routinely included in the USGS Mining Seismicity Report and an abundance of high quality regional seismic stations. A regional network of infrasound arrays was installed in order to quantify the accompanying low-frequency acoustic signals. In-mine seismic and acoustic measurements were made to quantify the source. These observations were supplemented with GPS locked video and in-mine documentation of the explosion design parameters. This comprehensive data set has been used to estimate source parameters that can be used to interpret the regional signals. Infrasound signals observed over a one-year time period indicate that the direction of atmospheric winds controls the amplitude and thus detection of these signals. Regional seismic observations are strongly affected by the style of blasting. The largest of the ground truth events (~250,000 kg explosive) are detonated in relatively long blasting sequences (~2 seconds) and produce some of the smallest regional signals. Smaller blasts (~25,000 to 50,000 kg) are detonated over relatively shorter time periods (`~0.2 to 0.4 seconds) and produce the largest regional signals. This source time function signature in the regional seismograms results in little relation between total explosive weight and peak regional amplitudes. Event locations based on the regional seismic network produces a location bias that is magnitude dependent and spans a region with a radius of over 30 km. Part of the location bias appears to be a result of improper identification of the emergent onset of the smaller events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.S12A0592S
- Keywords:
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- 7219 Nuclear explosion seismology