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Source parameters of seismic events potentially associated with damage in block 33/34 of the Kiirunavaara mine (Sweden)

Nordström E., Dineva S., Nordlund E.

Acta Geophysica

2017

Vol. 65, no. 6

1229--1242

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 × 10 7 J, the source radii from 4 to 110 m, the apparent stress from 6.2 × 10² to 1.1 × 10 6 Pa, energy ratio (Es/Ep) from 1.2 to 126, and apparent volume from 1.8 × 10³ to 1.1 × 10 7 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 nonshear (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.