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.

Valerijs G. Ņikuļins reports on  seismological monitoring in Latvia for the Summary of the Bulletin of the ISC.

The focal-mechanism solution for the second shock of the Kaliningrad earthquake on 21 September 2004 (13:32 UTC) with a magnitude of Mw 5.2 was obtained using the waveform inversion (WFI) method. The method was used with the aim of its subsequent application as a discriminator in the East Baltic region for recognizing the genesis of seismic events based on data from a limited number of stations. The WFI method was tested by broadband channels. The results of focal-mechanism solution (strike = 119°; dip = 73°; rake = –163°) allowed (1) to state the source mechanism as a right-lateral strike-slip, (2) to estimate the optimal source depth equal to 3.0 km, and (3) to estimate the parameters of the compression axes (Paz = 340°; Ppl = 29°), tension (Taz = 252°; Tpl = 1°) and the axis coinciding with the intersection of two nodal planes (Baz = 162°; Bpl = 66°). These results are in satisfactory agreement with the results of the leading seismological agencies. Seismotectonic analysis showed that the epicentre of the earthquake is located inside the structure formed by the Yantarnensk fault zone and the zone of the Bakalinsk ruptured flexure. The WFI method showed its potential use as a discriminator of the genesis of seismic events.

The aim: Determination of focal mechanism of Lithuanian earthquake of 12.06.15 (t0 = 08:18:26.4; 55.52° N, 21.40° E; hs = 0.9 км.; ML = 2.6) by waveform inversion using direct waves and a limited number of stations. Method: Matrix method is used for modelling of seismic wave propagation in the medium modelled as horizontally layered heterogeneous elastic structure. There were obtained the relations of displacement waves on the free surface that were used for seismic tensor determination using only direct P- and S- waves. Determination of seismic tensor and the focal mechanism on the base of developed method for a point source is described. Thus, based on forward modeling, numerical techniques are developed for the inversion of observed waveforms for the components of moment tensor. Results: In the paper, a method is presented for the focal mechanism determination of Lithuanian earthquake of 12.06.15 (ML = 2.6) by waveform inversion using limited number of stations. The focal mechanism is determined using the data from two stations: PABE, SLIТ and from three stations: PABE, MTSE, SLIТ. These seismic stations are the part of BAVSEN (BalticVirtualSeismicNetwork). Scientific novelty: 1. In the paper, a method is presented for moment tensor inversion for the focal mechanism determination of events with a low seismicity. The East Baltic region (EBR) is the region with low seismicity. 2. The focal mechanism is determined using the data from a limited number of stations. Practical significance: The results of focal mechanism determination can be used to study seismicity for regions with a low seismicity using a limited number of stations.

Geodynamic hazards of Latvia were identified by experimental and computational methods, including tectonophysical modeling in the MathLab environment. Among these factors are seismic shocks in Riga on November 22, 2010, abnormally high velocity of displacement of opposite sides of the Cirulisi fault, an increased anomaly of radon concentration on the profile crossing Olaine-Incukalns fault, deformations of buildings in the tectonic zone, formed by Olaine-Incukalns and Bergi faults. An analysis of the isostatic equilibrium of the Earth's crust at the Moho discontinuity level allowed to estimate Earth's crust development's and tendency type. On the basis of the analysis of experimental data and the results of tectonophysical modeling, a depression site was discovered in the area at the Plavinas dam. The conclusion is made about the expediency of geodynamic monitoring in areas of large agglomerations (Riga) and especially responsible objects (Plavinas dam, Incukalns underground gas storage).