Physics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994georl..21.1503f&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 21, no. 14, p. 1503-1506
Physics
4
Granite, In Situ Measurement, Q Factors, Ratios, S Waves, Seismic Waves, Seismograms, Seismology, Spectral Methods, Curve Fitting, Estimates, Least Squares Method, Mathematical Models, Propagation Velocity, Sh Waves, Wave Propagation, Wave Scattering
Scientific paper
An experiment to measure quality factor (Q) in-situ was carried out at the Underground Research Laboratory in Manitoba, Canada using the Spectral Ratio technique and a form of the Multiple Lapse Time Window Analysis technique. The volume of rock examined measures approximately 30 x 30 x 30 m at a depth of 420 m in Lac Du Bonnet Granite. The site encompases 16 triaxial accelerometers grouted in the bottom of boreholes drilled from access tunnel walls. The source for the seismic pulses was a mechanical hammer placed at the bottom of specially located boreholes. Results from the Spectral Ratio experiment gave S-wave quality factor Q(sub Beta) of 114 +/- 18. Based upon the short duration of the first arrival pulses and low scattered wave energy in the signal coda, we conclude that the Spectral Ratio technique measured the intrinsic attenuation of the rock mass. Further analysis using the more recently developed Multiple Lapse Time Window Analysis gave results for intrinsic Q(sub Beta) (Q(sub i)) of bewteen 85 and 100. Conversely, values for scattering Q(sub Beta) (Q(sub s)) were greater than 800. The high correlation for Q(sub i) values between the two methods help to confirm the nature and absolute values of the attenuation, and also support the use of the later technique where spectral ratios cannot be applied.
Feustel Andrew J.
Young Paul R.
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