Seismicity of the East Baltic region after the Kaliningrad earthquakes on 21 September 2004

Valerijs Nikulins, Bela Assinovskaya
Abstract For a long time, the north-western part of the East European Craton, specifically the East Baltic region (EBR), was considered an aseismic territory. Historical earthquakes did take place in the EBR, but they occurred rarely and could not always be associated with tectonic conditions. The attitude towards seismicity of the region began to change after the Osmussaar earthquake on 25 October 1976 (M = 4.7) and especially after the Kaliningrad earthquakes on 21 September 2004 (Mw = 5.0; Mw = 5.2). In this study, the seismicity of the EBR was generalized over 13 years after the Kaliningrad region earthquakes on the basis of Scandinavian and our own data. In several cases focal mechanisms were solved for weak earthquakes. The study showed a tendency of seismic activity to decrease from northwest to southeast, a predominant concentration of earthquakes sources in the East Baltic coastal zone, and the activation of Ladoga-Bothnia, Vyborg, Olaine-Inčukalns, Võrtsjärv zones. The main problems are associated with a rare seismic network, high level of ambient seismic noise, and a large number of man-made sources.
Keywords · East Baltic region · Fennoscandian region · GEOFON · Baltic Virtual Seismic Network · earthquake focal mechanism · crystalline basement · man-made earthquake · seismotectonics