HR: 13:55h
AN: S53C-02    [Abstracts]
TI: Source Parameters of Mining-Induced Microearthquakes at 1.4 km Depth
AU: * Oye, V
EM: volker@norsar.no
AF: NORSAR, P.O.Box 53, Kjeller, 2027 Norway
AU: Bungum, H
EM: hilmar.bungum@norsar.no
AF: NORSAR, P.O.Box 53, Kjeller, 2027 Norway
AU: Roth, M
EM: michael.roth@norsar.no
AF: NORSAR, P.O.Box 53, Kjeller, 2027 Norway
AB: Mining-induced seismicity bridges the gap of magnitudes between acoustic emissions measured in laboratory experiments and tectonic earthquakes. Source parameters of mining-induced microearthquakes therefore provide important information for earthquake scaling relations. We have automatically processed about 30,000 events from the 1.4 km deep Pyhaesalmi ore mine in Finland from the years 2003 to 2005. About two thirds of the events are production blasts and one third is mining-induced microseismicity. 18 geophones were installed in the mine at depths from 1.2 to 1.4 km and source to receiver distances were determined to be about 25 to 450 meters. All events were automatically located using P- and S- wave onset picks and polarization angles of the P-wave onset. Basic source parameters such as the seismic moment, the corner frequency, the radiated seismic energy and stress drops were determined automatically using a spectral integration technique and assuming constant Q. The seismic moments that we determined range from about 5*e6 to 5*e10 Nm. The corner frequencies vary from about 30 to 700 Hz. The ratios of the radiated seismic energy to the seismic moment range from about 3e-8 to 1e-5 and slightly increase with seismic moment. We applied the spectral decay method to a subset of about 45 events from two distinct clusters. The estimated Q(f) clearly increases with frequency. For the same subset we used the Multiple Empirical Greens Function (MEGF) method to determine the source parameters, and the results support the increase of Q with frequency. The ratios of radiated seismic energy to seismic moment, based on the MEGF approach, seem to be constant. These ratios, however, are at least two orders of magnitude lower than those of tectonic earthquakes.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005