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Earthquake-induced deformations located near Murmansk City were investigated for information on the age, tectonic position and spatial occurrence of paleo-earthquakes. The main earthquake-generating zone is identified to be the system of strike slip faults and reverse-oblique faults trending NNW along the Kola River valley. We used radiocarbon analysis and paleogeographic reconstructions and revealed three episodes of increased seismic activity: from 9500 to 10 500 cal BP, from 892 to 1182 cal BP, and from 200 to 300 cal BP. Based on the peak ground velocity estimation method we suggest that an earthquakes with a maximum moment magnitude up to Mw ≈ 6.0-6.5 may have taken place in the studied area. The recorded location of seismogenic deformation near faults indicates area of strong Late Glacial and Holocene earthquakes occurring in the northern Kola Peninsula; this is also consistent with observations concerning the historical events of 1772 and 1873, which took place near the area. Combined with previous data on palaeoseismicity in Kola region, our studies indicate a longer lasting and more complex spatial and temporal history of postglacial seismicity in the Northeastern Fennoscandian Shield area. In contrast to the generally accepted opinion, strong seismic events occurred not only during the deglaciation period or immediately after it, but continued until the late Holocene and the last centuries. Glacial isostasy as a factor giving rise to stresses has become minimal by the present time, while the tectonic factor continues to be felt. [ABSTRACT FROM AUTHOR]

The territory of investigations is located in the SE periphery of the Fennoscandian Shield. It served as an arena of periodic significant restructuring of the hydrographic network associated with the filling and discharge of large late-glacial and Holocene basins during the degradation of the Scandinavian ice sheet and in postglacial time. One such restructuring is a sudden change of the Saimaa Lake direction of flow in the middle Holocene from the west to south to the Lake Ladoga basin via the drainage hollow, inherited by modern Vuoksi River valley. Origin of the Vuoksi River is associated with the catastrophic water breakthrough of the Saimaa Lake across the marginal ridge Salpausselkä I of about 5.7 cal. kyr BP. This event usually connects with water accumulation and overflow due to non-uniform post-glacial uplift according to modern concepts. The authors propose a great earthquake as the immediate cause of the break waters of Saimaa Lake. This suggestion is based on the study of specific deformations of the rocky riverbed in the area of breakthrough and of the loose deposits in the banks of the Vuoksi River valley downstream. Open cracks and horizontally displaced rock blocks were discovered in the area of the former rapids near town Imatra. Their systematic displacements on the both sides of the rocky gorge indicate the shear kinematics of fault zone. Different types of deformations had occurred in loose sediments of the low terraces (3-4 m) in the Vuoksi River valley and 20-30 km below the headwaters. In three studied stratigraphic sections the three cardinal different types of deformations were discovered: 1) normal fault with vertical displacements, 2) tectonic inclination, and 3) traces of catastrophic mudflow. The time diapason of the terrace forming (and of the corresponding deformations) is determined of 8.3 to 1.8 cal. kyr BP (by the ages of adjacent terrace levels), which corresponds to the origination time of the Vuoksi River. The earthquake, which presumably was a trigger for the formation of the Vuoksi River, was generated by the activation of ancient fault zone, manifested in the crystalline foundation. Periodic post-glacial tectonic activity of this zone is revealed in traces of strong seismic events both in the bedrock (initial emergence of the gorge, its renewal during the breakthrough), and in loose deposits (deformations in different levels of terraces). [ABSTRACT FROM AUTHOR]

The area under study is located in the south-eastern periphery of the Fennoscandian crystalline shield. At present this is a tectonically quiet region without large seismic events. But it is well known that in post-glacial time the Fennoscandian shield was an arena of active postglacial tectonics and large earthquakes. The evidence for such events was found in various parts of Fennoscandia. The traces left by some paleoearthquakes show an undisputed character of large post-glacial faults some tens of kilometres long and of a few meters in displacement. However, some other features left by earthquakes are under discussion. Numerous deformations in bedrock and in soft sediments which can be considered as being due to earthquakes were found in the Russian Karelia. Interpretation of some of these deformation structures can lead to different conclusions about their origin, for example, weathering, cryogenic, glacial, and gravitational factors. One possible way to overcome these difficulties is an integrated study of different types of deformations at key sites, comparison of these with each other and with the tectonic features of the region, and the search for common structural and kinematic features. Another problem is the estimation of parameters of paleoearthquakes. This problem includes the determinations of their location, intensities, magnitudes, and age. The key site under study is located in the northern part of the Karelian Isthmus in the re-activated (during post-glacial time) tectonic zone (the Vuoksi Fault Zone), whose signature in the relief is seen in the form of the straight-line valley of the Vuoksi River. We studied different types of post-glacial seismogenic deformations at this locality. There are seismically induced gravitational and vibrational deformations in solid rock, as well as folds and ruptures in loose sediments. The key site of large deformation examined here includes three zones: 1) the main zone of deformations or the Central Fractured Massif (CFM); 2) the seismically induced colluvial zone; 3) the outer zone of deformations in loose sediments. We have established that all types of deformations are kinematically similar in the CFM and around it (at distances of a few kilometres). A detailed examination of deformations and their spatial and temporal relationships allows us to distinguish three generations of earthquake-induced deformations: 1) Late Glacial, 2) Early Holocene, and 3) Middle to Late Holocene. We estimate the intensities of the respective earthquakes as I=IX, IX, and VII-VIII. Clearly, the intensities decrease from post-glacial to present time, but the recent level of seismicity is unclear and may be much higher than hypothesized. In addition, the evidence for shear kinematics of the fault shows that earthquakes were not only caused by post-glacial rebound, but also resulted from a different tectonic mechanism possibly related to plate tectonics. [ABSTRACT FROM AUTHOR]