Quantification and interpretation of seismicity

Methods based oil acoustic emission and microseismicity (AE/MS) have proven to be valuable for monitoring microcracking at the Underground Research Laboratory (URL) in Canada. The source locations of the seismic events induced by the excavation have helped to map out the extent of the excavation damage/disturbed zone (EDZ) around tunnels. This paper describes methods for advanced processing and interpretation of AE/MS data, and the quantification of changes in Material properties using velocity interferometry. Examples of methods that are generally not used routinely, in the analysis of AE MS data are given. These include (1) long-term spatial and temporal source parameter trends and magnitude-frequency studied: (2) source mechanism analysis: and (3) source location refinement by the use of relative location. and clustering techniques. Results from these studies are shown to aid in the understanding of the effect of confining pressure oil AE/MS activity around tunnels and the mechanics of rock failure in the EDZ. Also, the reduction Of Source location error is shown to be critical for delineating structure that may exist in clusters of AE MS data. Finally, examples of the Use Of Seismic Sources to produce repeat measurements of seismic velocity along raypaths in 3D orientations through a rock mass are given. This is found to be a highly sensitive method for quantifying changes in rock properties such as Young's modulus as well as for modelling the change in crack density and maturation ocurring in a rock mass with time. (C) 2004 Elsevier Ltd. All rights reserved.