Analysis of time and frequency domain of mining induced seismicity at Kidd Creek Mine, Ontario

The complex structural geology and deep mining level at the Kidd Creek Mine leads to increased levels of rockburst activity. A full waveform analysis of mining induced seismicity was therefore proposed to Kidd Creek Mine of Falconbridge Ltd. by CANMET. Five hundred and ninety-one events were recorded by a portable seismograph (PDAS) between March and September 1991. Forty events were retained for analysis, consisting of mining induced seismic events and a few blasts. Three types of waves were recorded: P- or compressional, S- or shear, and surface waves. The latter are rarely recorded in mining seismicity because the sensors are usually glued to bedrock. However, surface wave propagation at Kidd Creek was recorded by a triaxial accelerometer placed on the concrete floor of a storage room. Thirty-nine of the forty events recorded by the PDAS were also recorded by the Kidd Creek MP-250 rnicroseismic system, and located using CANMET's BBLOCK program. Sixteen of these events were also located using the simplex algorithm. The two source location methods agree to within a few meters. On June 27 1991, a major rockburst of magnitude 2.6 Mn was recorded by the PDAS, (which because of a power failure, was not recorded by the MP-250). The source location was estimated to be 441 meters away from the PDAS. The source mechanism had a significantly higher shear than compression-dilatation component as illustrated by the energy content of the P- and S-waves. The magnitude of events was estimated from the energy values with the events greater than 1.4 Mn being confirmed by the Geological Survey of Canada in Ottawa. An attempt to analyze the data in the frequency domain was made but due to short source-receiver distances, i.e., less than one kilometre, this analysis could not be performed. This was because the frequencies contained in the waves were higher than the maximum sampling rate and higher than the 200 Hz hardware filter cut-off frequency, intrinsic to the PDAS. However, recognition of this fact would enable a reasonable analysis of data to be done for any future study either by placing the PDAS further away from the seismic activity or by designing a more adequate instrument.