Abstract

Four earthquakes with magnitudes between 2.3 and 3.0, which occurred between November 1979 and August 1980, are correlated with a potash mining operation near Saskatoon. Previous seismicity in the region is unknown. Detailed intensity surveys constrain the epicentres over, or close to, the periphery of the underground mining excavations. From microearthquake recordings over the mine, and from an analysis of short-period surface waves recorded for the March 18 event, focal depths are constrained to the region above the excavation. Microearthquakes show both temporal and spatial correlations with the mining activity. The results indicate that the relatively competent carbonate rock above the mine is spasmodically undergoing brittle failure or sudden rupture (presumably normal faulting) due to induced changes in the local stress–strain regime as a result of the mining excavation and the accompanying subsidence in the mine overburden.

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