Temporal changes in stress state imaged through seismic tomography

摘要

In order to understand how the rock mass evolves with extraction in the particularly highly stressed environment of a sill pillar in a hard rock mine in North America, we investigate the utility of seismic tomography as an interpretive tool. We use a rich dataset of blasts to highlight the compressional wave variations in the rock. To understand the optimal spatial resolution, we use checkerboard tests with our input ray path distributions. Although there are areas within the sill pillar that are prone to smearing, we are able to resolve subtle variations in velocity structure. By considering different time periods, we image temporal changes in seismic velocity that we relate to the stress state and damage in the rock. Specifically, we consider data recorded during three sequential time intervals, each consisting of three months of data, associated with the excavation of a stope during the start of the second interval. We observe a high-velocity anomaly in the first time interval that is located to the edge of the future stope. After mining, the high-velocity regions migrate to the other side of the stope and then disperse to the edges of the resolvable area. Equating high-velocity anomalies with high stress gives us the ability to characterise the evolving stress state in the mine and potentially an approach that can be used to avoid hazardous situations.