Microseismicity related to potash mining

Abstract

A seismic monitoring array was operated over the Potash Corporation of Saskatchewan Mining, Cory Division potash mine just west of Saskatoon, Canada in the thirty-nine month period October, 1981 through December, 1984. The array was set up to investigate macro- and micro-earthquakes that occur regularly near the mine. 83 micro-earthquakes and one macro-earthquake were recorded during the monitoring period. In order to compute accurate locations for the events recorded a suitable earthquake location algorithm had to be found; standard linear location strategies could not be used, because severe refraction of the energy travelling from hypocenter to receiver rendered the problem non-linear. A method of iterative approximation was therefore developed, by which P-wave arrival times observed at the seismometer stations are compared to calculated arrival times. The method makes use of the Simplex Algorithm to home in on the point in space which gives a "best-fit" (between calculated and observed times) with a minimum of computation. Locations were determined for 72 of the 83 micro-earthquakes recorded. Events were mostly located near regions of active or recent mining, with a few events located near regions of local geological disturbances. Estimates of local event magnitude were made for the 72 located events. Study of the frequency of occurrence of the events, and of magnitude relationships, imply that Cory micro- and macro-earthquakes are fundamentally different. The relationship between micro and macro events is not yet clear.