Abstract
Forty-six mining-induced seismic events with moment magnitude between −1.2 and 2.1 that possibly caused damage were studied. The events occurred between 2008 and 2013 at mining level 850–1350 m in the Kiirunavaara Mine (Sweden). Hypocenter locations were refined using from 6 to 130 sensors at distances of up to 1400 m. The source parameters of the events were re-estimated using spectral analysis with a standard Brune model (slope −2). The radiated energy for the studied events varied from 4.7 × 10−1 to 3.8 × 107 J, the source radii from 4 to 110 m, the apparent stress from 6.2 × 102 to 1.1 × 106 Pa, energy ratio (Es/Ep) from 1.2 to 126, and apparent volume from 1.8 × 103 to 1.1 × 107 m3. 90% of the events were located in the footwall, close to the ore contact. The events were classified as shear/fault slip (FS) or non-shear (NS) based on the Es/Ep ratio (>10 or <10). Out of 46 events 15 events were classified as NS located almost in the whole range between 840 and 1360 m, including many events below the production. The rest 31 FS events were concentrated mostly around the production levels and slightly below them. The relationships between some source parameters and seismic moment/moment magnitude showed dependence on the type of the source mechanism. The energy and the apparent stress were found to be three times larger for FS events than for NS events.
Highlights
As the underground mining advances to greater depths, the stresses in the rock mass increase, and as a consequence the level of induced seismicity usually increases
Hypocenter residuals (m) largest change in the source parameters after the refinement was in the seismic energy (39% increase), followed by the apparent stress (24% increase) and less change in the seismic moment and its derivative, the moment magnitude (7 and 5% decrease, respectively)
The energy showed a good correlation with the seismic moment for both types of seismic events
Summary
As the underground mining advances to greater depths, the stresses in the rock mass increase, and as a consequence the level of induced seismicity usually increases. The hypocenter location, magnitude, radiated energy, apparent stress, source dimensions, etc., were calculated by manual processing (experienced human picking of P- and S-wave arrivals). A set of 2089 waveforms of 46 studied events were obtained together with a catalog of the routinely calculated seismic source parameters from the LKAB database. The parameters of the recent seismic events in Kiirunavaara mine are calculated routinely by IMS using data from 18 sensors for each event and the same software. In this study our aim was to improve the location accuracy as best as possible compared to the routine processing by more accurate picking of the arrival times, using data from more sensors with the best possible azimuthal coverage. Disabling of arrivals with highest residual errors if AHD > 3% and locaƟon residual > 20 m
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