UNDERGROUND APPLICATIONS OF SEISMIC MEASUREMENTS IN A SASKATCHEWAN POTASH MINE

The seismic refraction method is used underground in a Saskatchewan potash mine to monitor the thickness of the salt formation over the mine. Frequencies over 100 Hz characterize the seismic records. Mining machines create noise problems. Records are picked with 0.1 ms precision and a computer used to make the calculations. The statistical random error in the interpretation ranges from ±4 ft to ±15 ft for typical thicknesses of about 130 ft. Seismic techniques have aided in locating a nearly completed mine shaft with respect to existing underground workings. The geophysical work was originally intended as a verification and check against gross errors in the conventional surveying. Preliminary tests showed that the method would work with acceptable accuracy. Interpretation was made using only the relative time differences between geophones. The predicted position of the shaft center was 340±2 ft northeast and 235±10 ft northwest of a reference point. This compares with the actual position of 342.4 ft northeast and 228.5 ft northwest of the reference position determined upon completion of the shaft connection.