Structural Position and Parameters of the Paleoearthquakes in the Area of Vottovaara Mountain (Middle Karelia, Eastern Part of the Fennoscandian Shield)

The traces of strong earthquakes in the territory of Fennoscandia have been recorded by many scientists already for several decades. The seismogenerating paleostructures, such as postglacial discontinuities in the crystalline basement accompanied by a complex of deformations in the loose deposits are found in the territories of Sweden, Norway, and Finland that border Russia, in which case the spatial correlation of the postglacial faults and modern seismicity is established. Such structures have not yet been discovered in Russia, though the traces of strong earthquakes in the form of rock deformations and postglacial sediments are found by different groups of researchers over the whole territory of Eastern Fennoscandia. The obtained data make it possible to identify the linear zones of concentration of paleoearthquakes (seismic lineaments) that also occur in the modern relief and modern seismicity. However, the problem of postglacial seismicity remains a subject for discussions concerning the localization of the foci, their genesis, and regime. A remaining issue is also distinguishing between seismogenic, cryogenic, and glaciodislocations. The important questions that need to be solved include parametrization of paleoearthquakes and determination of their nature, structures, age, and magnitude. One of the key segments is the area of Vottovaara Mountain in Middle Karelia, which is a part of the Vottovaara–Girvas seismic lineament, where seismic dislocations were found earlier. For studying this probable paleo-focal zone in detail, remote sensing data, field geological and geomorphological observations, and computational methods for estimating the peak values of paleoearthquake mass velocities are used. The typical zones of development of different types of seismic deformations are revealed. A potential seismogenerating fault related to the northwest-striking Vottovaara–Girvas seismic lineament is found; its probable shear kinematics is determined from the ratio of pulse displacements of rock blocks on different wings of the fault. The sequence of a few strong events which occurred here in the interglacial and postglacial periods is identified. The effects of interaction between the seismic activity and the glacial exaration on the formation of the modern image of the focal zone are established. Using alternative approaches to estimating shaking intensity by the macroseismic INQUA scale, the scale by F.F. Aptikayev, and the nomogram by M.V. Rodkin, the intensity of the recent strong Early Holocene seismic event, which occurred here at 8.9 ka according to A.D. Lukashov, is determined. According to the agreed estimates, the intensity reached 9–10 points at a probable magnitude of 7.5–8. This work carried out using a number of new approaches developed by the authors makes it possible to characterize paleoseismicity in more detail.