Institute of Geology of Karelian Research Center of RAS (Petrozavodsk, Russia):

Sharov N. V., Head of Laboratory of Geophysics, Doctor of Geological and Mineralogical Sciences, e-mail: sharov@krc.karelia.ru

Shekov V. A., Deputy Director of Scientific Work, Candidate of Engineering Sciences

Seismicity is one of the most striking manifestations of modern tectonic activity. On the seismic demarcation map of Russia (ОSR-97), Karelia is shown as a zone of possible magnitude (5-7 seismic activity) with a recurrence period of 5000 years. Seismic activity is restricted to the Kandalaksha-Dvina palaeorift and to the Ladoga-Bothnian suture zone. In spite of a relatively low seismic activity level, the detailed study of Karelia is not only in theoretical and scientific interest, but is also in practical value which has increased markedly because the region has big industrial complexes, gas pipelines and hydrotechnical facilities.

The modern movements of the Earth’s crust (EC) in the Fennoscandian Shield are controlled by two basic factors: a) the vertical arched uplift of the shield in general; b) autonomous block movements. The arched uplift of the EC is a continuation of earlier movements, which were initiated in pre-Palaeozoic times. All EC blocks are involved in the general arched uplift of the shield. Many of these blocks simultaneously complete the disharmonic movements, which are purely individual relative to neighbouring blocks. According to the modern concepts, the seismic regime of a studied territory depends largely on the geodynamic effect of subduction and rifting zones on the relevant EC volume. The Fennoscandian Shield – Russian Plate transition zone – is most liable to modern geodynamic variations.

Although in Northwest Russia seismicity does not cause disasters, it can lead to emergency situations, such as burst of ground water or spreading of radioactive and chemical waste from repositories. It may happen the considering that there are many industrial enterprises, underground communications, gas pipelines as well as Leningrad and Kola Nuclear Power Plants (NPP) in this region.

The operation of a regional seismic network of short-period stations in Karelia has shown that CR II stations are cheap and can reliably monitor seismicity. The seismic records of local earthquakes and blasts in 15 quarries can be used by Finnish stations and by the Arkhangelsk and Murmansk seismological networks.