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1

Seismic event near Jarocin (Poland)

Lizurek G., Plesiewicz B., Wiejacz P., Wiszniowski J., Trojanowski J.

Acta Geophysica

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2013

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Vol. 61, no. 1

26--36

EN

The earthquake of magnitude ML= 3.8 (EMSC) took place on Fri- day, 6 January 2012, north-east of the town of Jarocin in Wielkopolska Region, Poland. The only historical information about past earthquakes in the region was found in the diary from 1824; apart of it, there was a seismic event noticed in the vicinity of Wielkopolska in 1606 (Pagaczewski 1982). The scope of this paper is to describe the 6 January 2012 event in view of instrumental seismology, macroseismic data analysis and known tectonics of the region, which should be useful in future seismic hazard analysis of Poland.

2

Seismic event of January 22, 2010 near Bełchatów, Poland

Wiejacz P., Rudziński Ł.

Acta Geophysica

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2010

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Vol. 58, no. 6

988-994

EN

The paper summarizes the findings about a seismic event on January 22, 2010, near Bełchatów, Poland, in terms of data, event location, magnitude and source parameters.

3

Podhale, Poland, earthquake of November 30, 2004

Wiejacz P., Dębski W.

Acta Geophysica

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2009

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Vol. 57, no. 2

346-366

EN

Earthquake of November 30, 2004, in Podhale region, southern Poland, was of unexpectedly big size in this area of weak seismicity. As Poland is considered a country of low seismicity, the earthquake has caused concern about seismic hazard in Poland, especially since it took place shortly after the even more unexpected Kaliningrad Region, Russia, earthquakes of September 21, 2004, that inflicted minor damage in northern Poland. The paper presents the findings on the Podhale earthquake which reached macroseismic intensity up to 7 and magnitude 4.7 (mb; ISC). The event was felt up to a distance of about 100 km and inflicted slight damage to buildings in its narrow epicentral area, thus evidencing its relatively shallow depth. The quake has been located near the village of Skrzypne, about 15 km west-southwest of the district capital Nowy Targ. The source mechanism has been found to be of dip slip normal fault type, although a problem remains of association of this mechanism with known tectonic dislocations in the region. The earthquake has been followed by a long series of aftershocks. Their distribution in time is also studied and the biggest aftershocks have been located.

4

Czy w Polsce potrzebna jest sejsmiczna norma budowlana?

Zembaty Z., Wiejacz P.

Czasopismo Techniczne. Budownictwo

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2007

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R. 104, z. 2-B

127-134

PL

Weryfikacja ryzyka sejsmicznego terenu Europy, podjęta m.in. w związku z wprowadzaniem od 2010 r. eurokodów w krajach UE, wskazała na istnienie zagrożenia sejsmicznego na terytorium Słowacji, Czech i Polski Południowej. W niniejszym artykule rozważa się, czy wzorem Słowacji lub Czech także na terenie naszego kraju nie należałoby wprowadzić odpowiedniej strefy sejsmicznej Eurokodu 8. Wstępna analiza ryzyka sejsmicznego terytorium Polski wskazuje, że choć powszechne wprowadzenie w Polsce normy sejsmicznej nie wydaje się uzasadnione, to jednak w procesie projektowania budowle specjalne i monumentalne (np. elektrownie atomowe i duże tamy) powinny być poddane sprawdzającym procedurom analiz sejsmicznych poprzedzonych szczegółowymi analizami ryzyka sejsmicznego.

EN

Year 2010 marks the beginning of the process of implementation of Eurocodes in the EU states. This includes also the Eurocode 8 dealing with seismic effects on structures. A wide scale verification of the European seismic risk revealed a minor and moderate seismic risk for Slovakia, Czech Republic and Southern Poland. The paper considers whether also Polish territory should be treated as potential Eurocode 8 seismic zone. An analysis of seismic risk suggests that although the data gathered so far do not suggest any necessity for conventional seismic building code to be applied on Polish territory, the special and monumental structures (e.g. nuclear power plants or big dams) may require more advanced analyses of their seismic risk and respective detailed seismic calculations.

5

Moment magnitude determination of local seismic events recorded at selected Polish seismic stations

Wiejacz P., Wiszniowski J.

Acta Geophysica

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2006

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Vol. 54, no. 1

15-32

EN

The paper presents the method of local magnitude determination used at Polish seismic stations to report events originating in one of the four regions of induced seismicity in Poland or its immediate vicinity. The method is based on recalculation of the seismic moment into magnitude, whereas the seismic moment is obtained from spectral analysis. The method has been introduced at Polish seismic stations in the late 1990s but as of yet had not been described in full because magnitude discrepancies have been found between the results of the individual stations. The authors have performed statistics of these differences, provide their explanation and calculate station corrections for each station and each event source region. The limitations of the method are also discussed. The method is found to be a good and reliable method of local magnitude determination provided the limitations are observed and station correction applied.

6

Trzęsienia ziemi w Obwodzie Kaliningradzkim, 21 września 2004

Wiejacz P., Dębski W.

Przegląd Geofizyczny

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2005

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Z. 1-2

77-90

EN

On 21 September 2004 the northeastern area of Poland has experienced two unusual earthquakes of magnitudes 5.0 and 5.3. The earthquakes have originated in the nearby Kaliningrad Region, Russia, across the state border. Although the damages were minor and no casualties have been reported in Poland, the appearance of such earthquakes in an area otherwise considered non-seismic and totally safe has caused much concern among of relief services and general population. The earthquakes will naturally cause reassessment of the seismic hazard for this area and will be subject to scientific analysis. This paper summarizes those investigations of the events that result from everyday seismological observatory routine, providing information on location and magnitude of the events. The source mechanism is also being discussed. The results are an evidence that the Kaliningrad Region is a seismically active area, even though the earthquakes happen relatively seldom and do not reach devastating size.

7

Inner core attenuation observed at Polish broadband stations

Ivan M., Wiejacz P.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 3

231-238

EN

The amplitude spectral ratio of PKPdf and PKPbc phases recorded at Pol-ish stations from some strong deep Kermadec/Fiji earthquakes is used to derive the attenuation at the top of the inner core. The derived mean value of QP is 314š46 (95% confidence level) and the maximum depth of penetration of the PKPdf phase into the inner core is roughly 341 km. The sampled region of the inner core is centered beneath the Kuril Islands and North East of Japan.

8

Preliminary investigation of the September 21, 2004, earthquakes of Kaliningrad Region, Russia

Wiejacz P.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 4

425-441

EN

On September 21, 2004, the northeastern area of Poland has experienced two notable earthquakes of magnitudes 5.0 and 5.3. The earthquakes have originated across the state border in the nearby Kaliningrad Region, Russia. Although the damages were minor and no casualties have been reported in Poland, the appearance of such earthquakes in an area otherwise considered non-seismic and totally safe has caused much concern on behalf of relief services and population in general. The earthquakes will naturally cause reassessment of the seismic hazard for this area and will be subject to scientific analysis. This paper summarizes those investigations of the events that result from everyday seismological observatory routine, providing information on location and magnitude of the events. The source mechanism is also being discussed. The results evidence that the Kaliningrad is a seismically active area, even though the earthquakes happen relatively seldom and do not reach devastating size.

9

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.

10

Seismological station Kalwaria Pacławska (KWP): first year of activity

Wiejacz P., Suchcicki J., Jankowska W.

Acta Geophysica Polonica

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2001

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Vol. 49, nr 2

189-201

EN

The Institute of Geophysics, Polish Academy of Sciences, in cooperation with the GeoForschungsZentrum Potsdam, has set up in 1999 a new seismological broadband station at Kalwaria Pacławska (KWP), southeast Poland. The site was chosen as there are few seismological broadband stations in the area. Those that exist are either situated to the west or have outdated equipment and report data irregularly, as it is the case with the stations to the east. Therefore, Kalwaria Pacławska is very valuable to monitor local and regional seismicity in the area. The site is located on the edge of the Carpathians and has proven to be very interesting. During the first year of activity many seismic events from different parts of the world have been registered, the most noteful being perhaps the disastrous M = 7.4 earthquake that hit Izmit, Turkey. Surprisingly, some mining events from Upper Silesia and Lubin get registered fairly well on KWP. Attempt to describe the anisotropy beneath the station using SKS waves of events from 90-130 degree distance has yielded an interesting though ambiguous result. Hence, the anisotropy beneath KWP should be an issue of further study.

11

Temporary seismic station Czajcze (CZA) in Poland, 1997-1999

Wiejacz P.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 2

207-214

EN

Temporary seismic station "Czajcze" in northwestern Poland operated in the years 1997-1999. This paper is a summary of its activity and various issues encountered, and of the seismic events recorded in the period of its existence.

12

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.