Signs of Seismicity and Neotectonic Activity of Ancient Faults in the Area of the Sloboda Geodynamic Intersection in the West of the East European Platform

This paper presents results of multidisciplinary geochronologic, paleoseismic, and tectonophysical studies for local structures in the Sloboda tectono-dynamic intersection that is a segment of the junction between major tectonic structures in the East European Platform. These studies were conducted in the area of the Vitebsk–Surazh fault in the central part of the Sloboda intersection. This ancient long-lived discontinuity can be traced using geophysical data in the Precambrian basement. Activation during the platform phase of evolution made the fault penetrate the sedimentary deposits and form a negative flower structure showing signs of tectonic inversion. Since the Late Devonian until the beginning of the Quaternary, the Vitebsk–Surazh northeast striking fault has experienced at least two phases of tectonic activity in a setting of left lateral transpression and right lateral transtension. The Late Pleistocene to Early Holocene evolution of the Vitebsk–Surazh fault gave rise to the formation of graben-like hollows where late glacial and post-glacial lacustrine deposits were accumulated. The Gralevo Quarry shows horizons of seismites, indicators of paleoearthquakes, in the structure of these sediments. The earthquake of the highest intensity has been identified in the seismite structure of Early Holocene varved clay whose radiocarbon age is 9339 ± 36 years. The tectonophysical parameters of this seismic event are in agreement with conditions of normal-oblique deformation with a nearly east–west orientation of the tension axis and a nearly north–south orientation of the compression axis.