Bulletin of the Seismological Society of America
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Bulletin of the Seismological Society of America; February 2006; v. 96; no. 1; p. 272-287; DOI: 10.1785/0120050068
© 2006 Seismological Society of America
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Characteristics of Regional Seismograms Produced by Delay-Fired Explosions at the Minntac Iron Mine, Minnesota

Tom T. Goforth1, Claus H. Hetzer2 and Brian W. Stump3

1 Department of Geology
Baylor University
One Bear Place, #97354
Waco, Texas 76798
tom_goforth{at}baylor.edu
 (T.T.G.)

2 Infrasound Laboratory
University of Hawaii, Manoa
Kailua-Kona, Hawaii 96740
chetzer{at}isla.hawaii.edu
 (C.H.H.)

3 Department of Geological Sciences
Southern Methodist University
Dallas, Texas 75275
stump{at}passion.isem.sum.edu
 (B.W.S.)


Figure 001
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  		Figure 1. Examples of vertical-component, broadband seismograms produced by delay-firing at Minntac Mine, Mountain Iron, Minnesota, and recorded at Ely, Minnesota. The amplitude scales are in nm/sec.

 

Figure 002
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  		Figure 2. Broadband, vertical seismogram showing the arrival of Pg, Sg, and Rg/ Lg phases. The amplitude scale is in nm/sec.

 

Figure 003
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  		Figure 3. Broadband, vertical seismogram filtered into five one-octave passbands. The signal-to-noise ratio is excellent in each band. Peak particle velocities were measured in each band for both P and Rg/Lg phases. The amplitude scales are in nm/sec.

 

Figure 004
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  		Figure 4. Plots showing the scattered relationship of peak particle velocities to various expressions of yield. (a) Peak P-wave particle velocity on the vertical component in the 4–8-Hz band as a function of total explosive yield. (b) Peak P-wave particle velocity on the vertical component in the 4–8-Hz band as a function of average explosive per borehole. (c) Peak Rg/Lg particle velocity on the verticle component in the 4–8-Hz band as a function of average explosive per borehole. (d) Peak P-wave particle velocity on the vertical component in the 4–8-Hz band as a function of average spalled mass per borehole.

 

Figure 005
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  		Figure 5. (a) Peak P-wave particle velocity on the vertical component in the 4–8-Hz band as a function of average explosive per delay period. (b) P-wave energy in a 5-sec window on the vertical component in the 4–8-Hz band as a function of yield per hole.

 

Figure 006
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  		Figure 6. Comparison of the spectrum of event 108 and the noise in a 20-sec window preceding the signal.

 

Figure 007
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  		Figure 7. Examples of amplitude spectra of broadband, vertical seismograms produced by delay-firing at Minntac. (a) Event 108: total yield = 195,900 kg, yield/hole = 680 kg; (b) event 99: total yield = 286,300 kg, yield/hole = 2272 kg; (c) event 28: total yield = 249,150 kg, yield/hole = 1143 kg; (d) event 8: total yield = 464,325 kg, yield/hole = 1300 kg.

 

Figure 008
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  		Figure 8. Spectrum of event 108 with a linear frequency scale showing scalloping holes at intervals of about 0.52 Hz.

 

Figure 009
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  		Figure 9. Comparison of the recorded and theoretically modeled spectra, scaled to nm/sec/Hz, of event 8.

 

Figure 010
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  		Figure 10. Comparison of the recorded and theoretically modeled spectra of event 8 plotted as a linear function of frequency.

 

Figure 011
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  		Figure 11. Comparison of the recorded (dashed) and theoretically modeled (solid) spectra of event 7 scaled to nm/sec/Hz.

 

Figure 012
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  		Figure 12. Comparison of the recorded and theoretically modeled spectra of event 7 plotted as a linear function of frequency.

 

Figure 013
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  		Figure 13. Comparison of the theoretically modeled spectra of events 7 and 8 scaled to nm/sec/Hz.

 

Figure 014
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  		Figure 14. Comparison of the recorded (dashed) and theoretically modeled (solid) spectra of event 101 scaled to nm/sec/Hz.

 

Figure 015
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  		Figure 15. Comparison of the recorded and theoretically modeled spectra of event 101 plotted as a linear function of frequency.

 

Figure 016
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  		Figure 16. Comparison of the recorded spectra, scaled to nm/sec/Hz, of events 8 and 101.

 

Figure 017
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  		Figure 17. Comparison of the theoretically modeled spectra, scaled to nm/sec/Hz, of events 8 and 101.

 




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