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Comparison of source parameters estimated in the frequency and time domains for seismic events at the Rudna copper mine, Poland

Domański B., Gibowicz S. J.

Acta Geophysica

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2008

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Vol. 56, no. 2

324-343

EN

Source parameters estimated in the frequency domain for 100 selected seismic events from the Rudna copper mine, with moment magnitude ranging from 1.4 to 3.6, were collected to study their scaling relations and to compare them with the parameters estimated in the time domain. The apparent stress and static stress drop, corrected for the limited bandwidth recording, increase slightly in a similar manner with increasing seismic moment. The ratio of apparent stress to static stress drop, a measure of radiation efficiency, is practically constant and its mean value is close to 0.1. For 37 seismic events, with moment magnitude between 1.9 and 3.4, source parameters were estimated in the time domain from relative source time functions, that displayed unilateral rupture propagation, and their rupture velocity could be estimated. It ranges from 0.23 to 0.80 of shear wave velocity and is almost independent of seismic moment. The fault length, estimated from the average source pulse width and rupture velocity, is clearly dependent on seismic moment and is smaller than the source radius estimated from the corner frequency on the average by about 25 percent. There is no correlation between the values of static stress drop estimated in the frequency and time domains, but the time domain stress drop is in general similar to that estimated in the frequency domain. The apparent stress increases with increasing rupture velocity, and the ratio of apparent stress to static stress drop seems also to depend on rupture velocity.

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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

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2003

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Vol. 51, nr 4

347-367

EN

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.

3

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

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2003

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Vol. 51, nr 1

1-22

EN

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.

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An application of the pseudo-spectral technique to retrieving source time function

Dębski W., Domański B.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 2

207-221

EN

In this paper we discuss an application of pseudo-spectral approach to retrieving source time functions in a framework of the empirical Green's function technique. The method consists in a decomposition of the source time function into a set of suitably chosen base functions with decomposition coefficients estimated by a genetic algorithm based optimizer. The method, being essentially nonlinear, is compared with another nonlinear source time function deconvolution technique, namely the projected Landweber technique, by app1ying both algorithm to a Lubin copper mine seismic event. The pseudo-spectral method performs slightly better than the projected Landweber approach in the considered case, leading to smoother solutions.

5

Focal mechanism and source time function of selected aftershocks of the Egion 1995 earthquake, Gulf of Corinth, Greece

Gibowicz S., Domański B., Wiejacz P.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 1

1-25

EN

Numerous aftershocks, which followed the 1995 Egion earthquake of magnitude Ms = 6.2, were recorded by the seismic network PATNET of the University of Patras and by a temporary local network EGINET. The well recorded aftershocks were located by the Patras Seismological Centre, University of Patras. The complete data set, received from the Centre, contains the records of over a hundred events. The spatial distribution of their epicentres forms an E-W elongated cloud with a central cluster and a few stray-away epicentres west and north-west from the cloud. The events from the central cluster, which is the source area of the main shock, that occurred during the first decade of August 1995, were selected for the analysis. Additionally, a few events from the small cluster located west of the main one were also analysed. Altogether, it was possible to perform the moment tensor inversion in the time domain for 29 aftershocks from the main cluster and for 4 events from the small cluster. The selected aftershocks have moment magnitude ranging from 1.7 to 3.2. The source time function of the larger events was determined by the empirical Green's function technique. The records of several pairs of large-small aftershocks, close to each other and with similar focal mechanism, were selected for deconvolution. The source time function was recovered for 5 larger aftershocks from the central cluster and for 3 events from the small cluster. The small number of available stations used for the moment tensor inversion limit stable results to the constrained double couple solutions. The solutions show a mixture of various types of the focal mechanism, though dip-slip events prevail over strike-slip events, and normal faulting prevails over reverse faulting. The pulse widths of relative source time functions depend on the station azimuth, indicating that the ruptures propagated unilaterally. The azimuth of rupture direction ranges from about 90 to 250 degrees with the dominant direction of about 200 degrees. The fracture velocity ranges from 0.4 to 0.8 of the shear wave velocity. The obtained results indicate complexity of the stress distribution in the source area of the Egion earthquake.