3.6.4. Present-day stress regime and hazards

For most of the EEP the Neogene-Quaternary stress field is constructed mainly on the basis of mesostructures and topolineaments (e.g. Sim et al., 1995). These data reveal the impact of collision-related stresses on the southern margin of the platform in the domain of the Great Caucasus, in which shortening rates amount to some 14mm/y, giving rise to uplift rates of 8 mm/y (e.g. Nikishin et al., 2001; Kopp, 2005). On the EEP, E-W trending neotectonic structures are affected by horizontal compression (e.g. Zhiguli uplift), whereas N-S striking features appear to be tensionally reactivated (e.g. Orsha-Don depression).

There are only scarce instrumental data on the recent and present stress regime of the EEP, and these are mainly for its north-western part (World Stress Map, 2003). Available data suggest two stress provinces for the Baltic region. Borehole FMI and break-out data, earthquake focal mechanisms, and GPS measurements indicate that the western half of the Baltic Basin is characterized by a NW-SE orientated maximum horizontal compressional stress, similar to the Fennoscandian Shield, whereas N-S and NNE-SSW compression is indicated for eastern Lithuania, Poland, and the southern Baltic Sea (Jarosinski, 1994; Sliaupa et al., 2004). These stress provinces are thought to relate to North-Atlantic ridge-push and Alpine collision, respectively.

Though the tectonic activity of the EEP and related surface processes are of low intensity and are often neglected as the source of potential natural hazards, they nevertheless have to be considered in some cases, such as seismic risk assessment of nuclear power plants or repositories of nuclear wastes. Significantly, repeated GPS measurements in the vicinity of the Ignalina Nuclear Power Plant (eastern Lithuania) have revealed that inherited tectonic zones are characterized by high horizontal strain rates (Zakarevicius et al., 2005). A rather dense GPS network was established in Estonia, Latvia, and Lithuania in early 1990’s. A second cycle of measurements of country-scale GPS networks will provide crucial data for the understanding of on-going tectonic processes in the cratonic basement of these areas.

Assessment of the risk potential of cratonic areas remains a most difficult task, as recently highlighted by the Kaliningrad earthquakes of 21 September 2004 (ML=4.3 and 5.0). It should be noted that the maximum seismic risk potential of the Baltic region was assessed Io=5 at the time of construction of the Ignalina plant and was later reassessed to ML=4.6, which is less than that of the Kaliningrad earthquakes, for which the stress release was calculated as 32 MPa and 40 MPa. The GPS data around the Ignalina plant indicate that stress accumulation in some areas may be on the order of 10-1 MPa/a (Zakarevicius et al., 2005). Accordingly, the recurrence period of strong earthquakes along large-scale (inherited) fault zones could be some hundreds of years. Reassessment of the seismic potential and related risk is urgently required for the EEP.

Another group of significant hazards caused by tectonic activity is related to coastal processes. The short and long-term prognosis of uplift and subsidence trends and related coastal processes, many of which have considerable socio-economic impact, is in progress (e.g. Sliaupa et al., 2004).