Controlled sources for shear-wave surveys in mines

Abstract

The ability to analyse shear-wave anisotropy in a mine environment is greatly aided by using multiple source orientations of a reproducible, impulsive shear-wave source. The analysis of what is probably the first controlled source shear-wave experiment in a mine environment demonstrates clearly that shear-wave polarizations and time delays between split shear-wave arrivals are reliably measured because of the use of multiple source orientations rather than a single shear-wave source. Reliability is further aided by modelling the shear-wave source radiation pattern, which allows for the unequivocal discrimination between seismic raypaths where shear-wave splitting did and did not occur. The analysis also demonstrates the great importance of high reproducibility of the seismic source for the use of shear waves in time-lapse surveys to monitor changes in a rockmass.