Lietuvos geologijos tarnyba

The territory of the Baltic States and adjacent territories is regarded as of low seismic activity due to the Earth's crust of early Precambrian consolidation and large distances to the active tectonic zones. Nevertheless, according to historical and instrumental more than 40 local earthquakes of significant intensities took place since 1616 to present in the Baltic countries and Belarus (Fig. 1). List of seismic events was compiled by a group of scientist of Belarus and Baltic countries in 1988 (Avotinia et. al., 1988) and revised by Boborykin et al., (1993) later. Majority of events was revealed from macroseismic data of historical records. Therefore, some researchers argue tectonic origin of these events. Nikonov (1996) suggests that some earth's shakings of this list could be originated from bolts, karsts processes, land sliding, cryptogenic rupturing and meteor impacts.

Fig.1 Seismicity of the Baltic countries and nearby territories since 1616 to 2005. Filed circles correspond to historical events (Boborykin et. al., 1993), hexagons - instrumentally registered events, triangles - operating seismic stations.

The seismic activity of the territory of Lithuania is lower to compare with the nearby territories (Fig. 1). No event from the list is located on the territory of Lithuania. No local seismicity was detected by Vilnius seismic station during the period of thirty years either. Surprisingly, one local event was recorded by a Seismic Monitoring System of the Ignalina Nuclear Power Plant (INPP) on 4 th of September, 2001 (Fig. 2). The earthquake of local magnitude of 2.1 was recorded by single seismic station ISAL. Therefore, no exact location was possible to define. Difference of arrival times of P and S waves showed that the distance from station to epicenter was ~80 km. The seismo-tectonic structure of Lithuania and adjacent areas is not realized completely yet.

Earthquakes of moderate size (M=4.4 and M=5.0) shocked the Kaliningrad district of Russian Federation (neighboring to Lithuania) 21 September, 2004. A seismic trembling has been felt throughout all territory of Lithuania. These extremely rear and unusual phenomena have provoked great concern of mass media and public. Geological Survey of Lithuania analyzed data of international seismic agencies, processed data of Seismic Monitoring System (SMS) of Ignalina Nuclear Power Plant (INPP) and spread information within time of a few hours. Later a macroseismic investigation has been carried out and macroseismic map were compiled (fig. 3).

According to seismic bulletins of NORSAR and Seismological Institute of Helsinki University, a few dozens of explosion events are recorded by the seismic stations of Finish and Scandinavian countries. Vast majority of these events can be associated with mining, civil and military explosions.

Currently there are four seismic stations operating in Lithuania. They are located in the Northeastern part of Lithuania in the surroundings of the INPP and owned by INPP. The seismologic information of Lithuania is systematically collected and analyzed by specialists of the Department of Bedrock Geology in collaboration with the INPP.

The seismic network of INPP equipped with single-component short period seismometers is not capable to cover the whole territory of Lithuania with trustable resolution. The fact that no quarry blast (distance to INPP is ~200 km) was recorded by SMS of INPP evidences this issue. Obviously, the existing system of seismological observations is not sufficient while, Kaliningrad events have shown, earthquakes of moderate size could shake the Baltic region. At least a few more seismic stations should be installed in Lithuania, in order to monitor low seismic activity and potential seismogenic zones could be defined. Data collected by wider seismic network and additional knowledge of tectonics, geodynamics and hydrology should provide a basis assessing seismic hazard of the Lithuania.

18 September 2006 The Government of the Republic of Lithuania approved „The program of the assessment of the seismic structure of Lithuania for years 2007-2010“. The program is aiming to ensure the assessment of the structure of the territory of Lithuania in terms of the seismic activity, the persistent seismologic monitoring of Lithuania, establishment and support of the seismological monitoring network in Lithuania, joining the international seismic monitoring networks that allow providing the society and specialists with reliable seismological data and information.

Seismisity of the Baltic countries

Global seismisity