Paweł Wiejacz

New observations of Gulf of Gdansk seismic events

Abstract Seismicity of northern Poland and of the adjacent area of the Baltic Sea has been considered weak, if any. Historical reports mention just a couple of seismic events felt in the region, while observatory seismology has recorded just a single swarm of seismic events in the Gulf of Gdansk. The lack of information is caused not only by the weak seismicity of the area, but also by the lack of seismological observatories in the region. This situation is changing with the installment of a new seismological station Suwalki in northeastern Poland, and two temporary very broadband stations of the GEOFON network, one in northwestern Poland, and the other on Oeland Island, Sweden. Just months after the installations, we are able to detect and locate numerous seismic events in the Gulf of Gdansk. This does not necessarily mean that Gulf of Gdansk is a seismically active area, as there are indications that the events may be caused by human activity. One of the objectives of this paper was to obtain reliable location solutions with the best possible location error control. Since only a few stations are in operation in the nearby area and little is known about the velocity structure, the Bayesian inversion method has been used to locate event epicenters. This method allows to minimize location errors caused by insufficient knowledge of local crust velocity structure and non-Gaussian statistics of measurement/modeling errors. The method, being fully nonlinear, does not introduce instabilities typical for inverse approaches which uses linearization.

Source Time Function of Seismic Events at Rudna Copper Mine, Poland

Abstract — The empirical Greens function deconvolution technique is used to retrieve the source time functions from the records of P waves of seven seismic events that occurred at the Rudna copper mine in 1996 and were located in the middle of the underground network. Their moment magnitudes ranged from 2.1 to 2.9. The records of smaller events from the same area and with similar source mechanism, with moment magnitudes ranging from 1.5 to 2.0, were accepted as empirical Greens functions. The relative source time functions were successfully retrieved at a number of stations for six events. Directivity effects, implying unilateral rupture propagation, were observed in five cases. The azimuth of rupture propagation direction and the rupture velocity were estimated from the distribution of pulse widths and pulse maximum amplitudes as a function of the cosine of station azimuths. The rupture propagated approximately either from south to north or from north to south. The rupture velocity was low, ranging from 0.25 to 0.54 of the shear-wave velocity. The source dimensions, represented by the fault length, were also small in comparison with those estimated in the frequency domain and ranged from 80 to 250 m.

Moment Tensor Solution and Physical Parameters of Selected Recent Seismic Events at Rudna Copper Mine

The Lubin Copper Basin is a source of induced seismic events of considerable size. The paper presents the source mechanism study of fifty seismic events from Rudna Copper Mine that occurred in 2007. The energies of studied seismic events were greater than 105 J. Focal mechanisms for those events have been calculated with seismic moment tensor inversion method using FOCI computer software. The calculations were made using L1 and L2 norms. Final results are presented for L1 norm due to its lower sensitivity to possible errors. Spectral analysis of P and S waves was also performed. The analysis shows that typical focal radius is of about 200 m.

Seismic event near Jarocin (Poland)

The earthquake of magnitude ML = 3:8 (EMSC) took place on Friday, 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.

Seismology and Earth Dynamics: A Variety of Scientific Approaches

Seismology and related fields were among the basic disciplines constituting the Institute of Geophysics, Polish Academy of Sciences, from its inception. During 60 years, various experimental and theoretical researches have been conducted, and a network of seismic observatories has been managed and gradually updated, as part of international network. Novel theories of the propagation of seismic waves and the processes in the lithosphere and the Earth’s interior, especially in the seismic event preparation areas, have been developed and gradually modified. The statistical studies and profound research on innovative mathematical techniques brought about a real progress in the assessment of seismic hazard and the probability of other extreme events.