ROCK-MASS CHARACTERIZATION USING INTRINSIC AND SCATTERING ATTENUATIONESTIMATES AT FREQUENCIES FROM 400 TO 1600 HZ

Intrinsic and scattering S-wave quality factors (Q(beta)) were estimat ed using the Multiple Lapse Time Window Analysis (MLTWA) for microseis mic events (M < -1) with source-sensor distances of 45 to 120 m, assoc iated with an excavation at 630 m depth in Strathcona Mine, Sudbury, C anada. Additional information on the rock mass was provided by undergr ound structural mapping data. Intrinsic Q(beta) values, at 800 Hz, wer e on the order of 140, similar to quality factor values obtained in pr evious studies using Spectral Decay and Coda-Q methods (120 to 170). T he scattering quality factor at this frequency was about 520. An obser ved frequency dependence of the scattering attenuation suggested that a decrease in the density of scatterers, with scale lengths on the ord er of 2 m, exists at the site. Characteristic fracture scale lengths w ere considered to range from 4 to 6 m as identified in the mapping dat a. These observations were supported by the increase in scattering fou nd for seismic waves with frequencies less than 1000 Hz. By assuming t hat the identified scatters are characteristic faults, these scatterer s can then be considered to increase nonsimilar behavior in source sca ling. Overall, our results suggest that MLTWA provides a practical met hod for remotely characterizing the quality of a rock mass when visual observations are not attainable.