High Resolution Seismic Monitoring in Open Pit Mines

The Mt Keith operation comprises an open pit nickel mine with a planned depth of approximately 600 m. The pit bottom was about 355 m, with mining to the north of the array taking the pit bottom in that area from 155 m to 320 m during the monitoring period. The seismic array comprised six uniaxial accelerometers and six uniaxial geophones. Due to the higher frequency range, the accelerometers provided better source parameter estimates. The geophones, however, were more sensitive to the events outside of the array. The seismic system was damaged in April 2007, resulting in the loss of the six geophones. With the loss of the geophones, the sensitivity of the system to events outside the array was greatly reduced.

The project showed that MS monitoring can provide valuable insights into the brittle fracture process in rock slopes, from the stages of initial tensile fracture growth to shear on shear zones. It may also provide data for the calibration of numerical models and the further development of material models to capture the true brittle fracture and damage accumulation process that governs the behaviour of large rock slopes.

The seismicity at Mount Keith is limited to the first stages of brittle fracturing, attributed to pre-peak brittle fracture growth due to a generally extensional fracture process resulting from the stress change and dilative strain environment.