New observations of Gulf of Gdansk seismic events

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. (C) 2001 Elsevier Science B.V. All rights reserved.