TEMPORAL IMAGING OF MINE-INDUCED STRESS CHANGE USING SEISMIC TOMOGRAPHY

In an effort aimed at monitoring mining-induced stress changes that ma y influence ground failure, the US Bureau of Mines conducted a series of active 3-D seismic tomographic surveys at the Homestake (Lead, Sout h Dakota) and Lucky Friday (Mullan, Idaho) mines. Existing rock bolts were used to mount geophones and as strike points for introducing seis mic energy using a 3.6 kg sledge hammer. Travel time measurements were recorded spanning up to 160 m between drifts at several levels. The t omographic uncertainty was minimized by computing iso-velocity surface s of constant probability based on statistics from multiple reconstruc tions and a threshold criteria. Periodic imaging using tomographic vel ocity surfaces demonstrated that temporal and spatial changes in the l ocal stress field occurred in response to ground failure and stope adv ancement at a gold and silver mine, respectively.