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1

Seismic doublets and multiplets at Polish coal and copper mines

100%

Gibowicz S.

Acta Geophysica

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2006

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tom Vol. 54, no. 2

142-157

EN

The following criteria for selection of doublets at Polish coal mines were accepted: the difference in magnitude (based on seismic moment) of two events not larger than 0.15, the distance between their hypocenters not greater than 150 m, and the time interval between their occurrence not longer than 10 days. Similarly, the criteria for seismic events at copper mines are: the difference in magnitude not exceeding 0.15, the distance not greater than 200 m, and the time interval not longer than 20 days. Seismic events from the Wujek and Ziemowit coal mines that oc-curred between 1993 and 1995, and seismic events from the Polkowice copper mine that occurred between 1994 and 1996 and from the Rudna copper mine that occurred between 1994 and 2004 were considered. Their source parameters and focal mechanisms were known in most cases from previous studies. Altogether 108 seismic pairs from coal mines and 118 pairs from copper mines were found, forming doublets, triplets and quadruplets, within the magnitude range from 0.7 to 3.5. The distance and time intervals between two events forming pairs are not dependent on magnitude of these events. The focal mechanism of seismic events forming pairs is similar in over 60 percent of pairs at coal mines and in about one third of pairs at copper mines. Spa-tial distributions of doublets in particular sections of coal and copper mines display dominant linear trends, characteristic for a given area, which are often in conformity with the direction of nodal planes determined by fault plane solution of one or both the events forming a doublet. In such cases, the rupture plane can be discriminated among the nodal planes.

2

Apparent stress and stress drop from seismic events induced by mining

100%

Gibowicz S.

Acta Geophysica Polonica

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2002

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tom Vol. 50, nr 1

35-49

EN

Seven sets of the values of uniformly estimated apparent stress and Brune's stress drop from 987 seismic events, with moment magnitude ranging from -3.6 to 3.8, were collected from two South African gold mines, two Polish coal and two copper mines, and from the Underground Research Laboratory (URL) in Canada. They are used to examine their relations with radiated energy, seismic moment and source dimension to provide observational evidence of differences for slip-weakening as compared to velocity-weakening friction, found from elasto-dynamic source modeling of Shaw (1998). The observations from various data sets scale differently, but their pattern is not always distinctly related to the different frictions. The distribution of the apparent stress divided by the stress drop as a function of seismic moment is the most similar to the relevant distribution obtained by modeling, and it seems that both modes of friction are possible during the generation of seismic events in various mining environments.

3

Radiated energy scaling for seismic events induced by mining

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Gibowicz S.

Acta Geophysica Polonica

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2001

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tom Vol. 49, nr 1

95-111

EN

Seven sets of the values of radiated energy from 987 seismic events from two South African gold mines, four Polish coal and copper mines, and from the Underground Research Laboratory (URL) in Canada are used to examine their scaling with seismic moment, apparent stress and average displacement. Moment magnitude of these events ranges from -3.6 to 3.8, the seismic energy ranges from 1x10(-3) to 1x10(11) J, and the apparent stress is between 0.0025 and 5 MPa. The slope of regression straight line between the logarithm of radiated energy and that of seismic moment is very close to 1.5 in all cases, which seems to have theoretical justification. The average values of seismic energy, however, referred to the same range of seismic moment, are about 30 times higher for seismic events from South African hard-rock mines that those observed from events in Polish mines. Similarly, the slope of a linear regression between the logarithm of apparent stress and that of energy is fairly close to 1/3 for the events from South African and Polish mines. But the average apparent stress, referred to the same range of seismic energy, is about 10 times higher for the events in South Africa than for those in Poland. The relations between the average slip and the energy are on a logarithmic scale surprisingly consistent and more regular than similar relations based on seismic moment. The events from the URL follow the same trend as the events from South Africa, whereas for the events from Poland the average slip is about 5 times lower than that for the other events.

4

Stress release during earthquake sequences

100%

Gibowicz S.

Acta Geophysica Polonica

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2004

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tom Vol. 52, nr 3

271-299

EN

The average stress drop and apparent stress released during 65 complex earthquake sequences from all over the world are estimated separately for foreshocks, main shocks and aftershocks. All of them but one occurred between 1977 and 1997. The Harvard CMT solutions are available for 60 main shocks, 38 foreshocks and 218 aftershocks. The stress drop is estimated using the values of seismic moment and source half duration and the scaling relations between various source parameters: seismic moment, source half duration, fault surface and fault length, taken from Harvard catalogues and other publications. The average stress drop is the highest during foreshocks (1.8 MPa), middle during main shocks (1.1 MPa) and the lowest during aftershocks (0.4 MPa). Similarly, the apparent stress, estimated from seismic moment and radiated energy taken from PDE-NEIC bulletins and other publications, is also the highest for foreshocks (0.6 MPa), middle for main shocks (0.4 MPa) and the lowest for aftershocks (0.2 MPa).

5

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

63%

Domański B. , Gibowicz S.

Acta Geophysica Polonica

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2003

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tom 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.

6

Seismicity before and after the two great Sumatra earthquakes of 2004 and 2005

63%

Gibowicz S. , Dębski W.

Acta Geophysica

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2006

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tom Vol. 54, no. 4

343-360

EN

The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast. The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.

7

Comparison of source time functions retrieved in the frequency and time domains for seismic events in a copper mine in Poland

63%

Domański B. , Gibowicz S.

Acta Geophysica Polonica

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2001

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tom Vol. 49, nr 2

169-188

EN

The extraction of source time functions based on empirical Green's functions is especially convenient for source studies of seismic events in mines, where underground seismic networks are situated in the source area and are often composed of a large number of sensors. The empirical Green's function deconvolution techniques were applied to retrieve the source time functions from the records of P waves of several seismic events that occurred in 1998 at Rudna copper mine in Poland. The selected events were located within the underground network composed of 32 vertical sensors situated at a depth of about 1 km; the size of the network is about 10 by 10 km. Their moment magnitude ranged from 2.7 to 3.2. The records of smaller events from the same area and with similar source mechanism, with moment magnitude from 2.2 to 2.4, were accepted as empirical Green's functions. The results of classic deconvolution approach in the frequency domain are reported elsewhere. The results of the application of projected Landweber deconvolution in the time domain to the same set of data are described here. The projected Landweber approach is an iterative deconvolution technique, allowing introduction of physical constrains on the final source time function. This technique successfully overcomes the instability effects of the deconvolution process inherent in the frequency domain and provides stable and reliable relative source time functions retrieved at several stations. Although the results obtained in the frequency and time domains were found to be similar, the time domain approach provides more objective determination of the source time function duration, essential for a proper determination of the source dimension. The relative source time functions retrieved by both methods display directivity effects in several cases, implying unilateral rupture propagation. The rupture propagation direction and rupture velocity were estimated from the distribution of pulse widths and pulse maximum amplitudes as a function of the station azimuths.

8

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

51%

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

Acta Geophysica Polonica

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2003

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tom 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.

9

Temporal distribution, source parameters, and depth discrimination of earthquakes from the Abu Dabbab region, Egypt

51%

Hassoup A. , Niewiadomski J. , Gibowicz S.

Acta Geophysica Polonica

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2003

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tom Vol. 51, nr 2

135-146

EN

Records of earthquakes from the Abu Dabbab region in Egypt, situated about 25 km west of the Red Sea coast, were collected from the Aswan Seismograph Network (ASN). The temporal distribution of these events shows several sequences of the foreshock-main shock-aftershock type. Four such sequence occurred in 1984 and 1985. the slope of the frequency-amplitude relation (b-value) for the four sequences ranges form 1.8 to 2.4, reflecting co-seismic deformation with time in the vicinity of the source area. Source parameters were estimated for ten events from the same area, which occurred between 1998 and 2001 and had magnitude ranging from 3.0 to 4.2.the spectral plateau, corner frequency, seismic moment, source dimension, and stress drop were calculated. A good correlation is found between the logarithm of seismic moment and the local duration magnitude determined by the ASN. The stress drop is not uniform and ranges between 0.1 and 6.8 MPa. In addition, the relative decay of the amplitude of S waves from the Abu Dabbab earthquakes with the epicentral distance is examined from the records of various stations of the ASN. It was found the rater of decay can be divided into two distinct types, related to different paths between the hypocenters and the stations, which in turn indicate different depths of the studied events.

10

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

51%

Gibowicz S. , Domański B. , Wiejacz P.

Acta Geophysica Polonica

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1999

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tom 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.