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2 Acta Geophysica Polonica

2 2003

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The accuracy of source parameters estimated from the source time function of seismic events at Rudna copper mine in Poland

Domański B., Gibowicz S.

Acta Geophysica Polonica

2003

Vol. 51, nr 4

347-367

The source time function of43 seismic events from Rudna copper mine was retrieved using empirical Greem's function deconvolution technique in the frequency and time domains. Thirty four events were studied preciously and nine new events were added, with moment magnitude raging from 2.1 to 3.6. the records of smaller events from the same area, with moment magnitude ranging from 1.5 to 2.7, were accepted as Grees's functions. Bith methods, the spectral division and the projected Landweber deconvolution, provided consistent results, but from an error analysis it follows that the classec spectral division solutions seem to be more reliable than the Lndweber solution. The relative source time functions retrieved from the records of a number of seismic stations (from 10 to 42) by the spectral division for 32 events and by the Landweber deconvolution for 36 events display directivity effects, implying unilaterally propagating ruptures. The rupture propagation direction and rupture velocity were estimated from the distribution of pulse widths and pulse maximum amplitudes as a function of station azimuths. The rupture velocity ranges from 0.25 to 0.9 of the shear wave velocity. Its values can be divided into two distinct sets: low velocity values in comparison with those from natural earthquakes, between 0.25 and 0.6 of shear wave velocity, and high velocity values greater than 0.6 of the shear wave velocity. The rupture velocity depends also to some extent on the rupture direction.

Source time function of seismic events at Polish coal mines derived by empirical Green's function approach

Gibowicz S., Domański B., Nita B., Wiejacz P.

Acta Geophysica Polonica

2003

Vol. 51, nr 1

1-22

The empirical Gren's function deconvolution techniques in the frequency and time domains were applied to retrieve the source time functions from the records of P waves of 25 seismic events that occurred in 1994 and 1995 at Wujek coal mine and of 5 events that occurred in 1994 at Ziemowit coal mine. The selected events were located within the underground seismic networks composed at Wujek mine 14 vertical sensors, situated at a depth between 300 and 740 m and within the mining area of about 8 km2. the network at Ziemowit mine was composed of 16 vertical seismometers located at a depth between 430 and 620 m in the southern part of the mine. Moment magnitude of selected events ranged from 1.1 to 2.2. the records of several smaller events from the same area and with the similar source mechanism, with moment magnitude ranging from 0.3 to 1.7 , were accepted as empirical Green's functions. Both applied methods, the spectral division and the projected Landweber deconvolution, provided consistent and stable results. The relative source time functions of 6 events at Wujek mine and of 3 events at Ziemowit mine indicate that the rupture source propagated unilaterally, either along or perpendicularly to the longwall extension where the events were originated. The rupture velocity ranged from 0.4 to 0.8 of the S-wave velocity, which is distinctly lower than its typical value reported from natural earthquakes.