Seismogenic Activation of a Fault in the Late Neopleistocene by Deformations in the Topography, Sediments, and Basement Rocks in the Southeast of Fennoscandia

Abstract

Comprehensive studies of seismogenic deformations in the topography, sediments, and rocks of the crystalline basement using structural-geomorphological, geophysical, and tectonophysical methods have been carried out. Based on the materials of deciphering digital elevation models, a hierarchical block-fault structure has been established, which has been partially inherited and activated in recent times and corresponds to the topographic forms and linear accumulative formations (eskers and plumes) “inscribed” in the tectonic framework. Ruptures of different kinematic types, folds, and forms of liquefaction in gravel-sand deposits have been discovered and documented within one of the massifs. The separations of reverse faults reach 1–2.2 m; those of normal faults are 1.5–4.5 m. Eight horizons with deformations have been identified, the thickness of the largest of which is ≈4 m, and the age range according to OSL dating is from 53 ± 3 cal. kyr to 41 ± 3 cal. kyr. This horizon corresponds to the parameters of the paleoearthquake of IX+ points. Other deformation horizons have a thickness from 0.1 to 0.4 m and are formed by weaker events, one of which occurred before the maximum glaciation, while six occurred later, in the Late Glacial period. Ruptures can be traced in the sediment sequences with depths of up to the first meters according to geolocation data. In the crystalline rocks in the zone of the esker and the faults controlling it, crushing zones and sliding mirrors were found, indicating a consistent activation of faults. The strike-slip and reverse character of the ruptures with a northwesterly strike line and east–northeast and southwest dip azimuths corresponding to ruptures in loose sediments and the general latest structural plan has been established.