Identification of the Seismogenic Structure in the Area of Chupa (North Karelia) and Parameterization of Paleoearthquakes in the Kandalaksha Graben Region

Abstract

In the area of the village of Chupa, three isolated ranges of paleoseismic dislocations were revealed, marking a NW-trending linear seismogenic structure and a total length of more than 14 km . The dislocations are young tectonic ditches and fissures, mainly trending NW, mass displacements of blocks, including against the slope, disarrayed stones, and seismic landslides. Using the nature of the distribution of seismic dislocations for two areas, isoseismic maps were constructed, which made it possible to estimate the magnitudes of paleoseismic events using the macroseismic technique. They amounted to 3.7 and 2.9, respectively, with a focal depth of H ≤ 1 km under the assumption that each range corresponds to a local seismic source. The isolated character of the distribution of the identified ranges may be associated with another, more severe paleoearthquake, traces of which have been preserved mainly in elevated areas of the relief (above 80 m). In the Early Holocene, these sites were separate islands, since the formation conditions for dislocations were limited to subaquatic spaces. For this variant, M = 5.5 and H = 5 km were calculated; the age of the event is the Early Holocene. The results, taking into account data on the micrograben of the Great Salma Strait, indicate the periodic occurrence of coastal and mainland faults, subparallel to the axis of the Kandalaksha graben, as well as Holocene shallow-focus earthquakes of medium magnitude with an epicentral intensity up to I = VIII on the ESI-2007 scale. A catalog of postglacial paleoearthquakes of the Kandalaksha graben region has been compiled (5 events), which can be used to construct earthquake recurrence graphs. This will make it possible to substantially refine the seismic regime of this structure.