Induced seismicity in potash mining — a finite element study

Summary A number of earthquakes have been recorded in strata above underground potash mines in Saskatchewan, Canada. These seismic events are widely understood to be generated in the carbonate Dawson Bay Formation and, possibly, other superincumbent beds, and are believed to be directly related to mining operations. The mechanical response of these higher strata to mining is not observable andin situ instrumentation for measuring post-mining stresses and strains in the carbonate beds is sparse. Numerical models are believed to be the most effective option for investigating the response of these higher strata to potash mining. In this regard a realistic finite element model based on elasto-plastic material behaviour is developed in this paper. Special capabilities added to this general elasto-plastic model permit simulation of the post-failure behaviour of the rock mass. Possible modes of failure in the Dawson Bay are investigated and the brittle failure of intact limestone is affirmed as the possible mode of failure producing major seismicity. Slip along existing discontinuities in overlying strata is also demonstrated to be another possible mechanism, though with lower energy levels.