In 2023, Oleg Lavrov, Director of the Museum of Precambrian Geology at IG KarRC RAS, was contacted by residents of the Kubovo village in the Pudozh District, Viktor and Zulfiya Shevchenko, who reported unusual boulder debris shaped as caves and niches. Locals nicknamed the site as Kubovo megaliths, supposing its glacial genesis as well as use as ancient ritual structures. However, even after just looking at the photographs, scientists suggested it was most likely the result of an earthquake. To verify this hypothesis, Oleg Lavrov and employees of the Quaternary Geology and Geoecology Laboratory IG KarRC RAS Tatyana Shelekhova and Grigory Rodionov set out on an expedition expedition to the site.
– Exploring the location, we clearly saw this was a true paleoseismic case, and of postglacial genesis at that. Some 25 thousand years ago the load of a massive, 2.5 kilometers thick, ice sheet was melting away in the territory of Karelia, causing crustal movements. At the site, we saw hefty sharp-edged fractures and faults in granitoid rock outcrops, which had originally been smoothed down by the glacier, – related Tatyana Shelekhova, Head of the Quaternary Geology and Geoecology Laboratory at the Institute of Geology KarRC RAS.
Site with the newly discovered paleoseismic dislocation
The geography of the event per se is of great interest. Postglacial paleoseismic dislocations have been studied in different parts of Karelia. The best known is Mt Vottovaara. In south-eastern parts of the republic however no ancient earthquake locations had been discovered before.
– The area falls in the suture zone of major neotectonic structures – the Fennoscandian Shield and the Russian Platform. Here, ancient Precambrian rocks dip under a sedimentary sheath, so there are no such pronounced uplands or rocky areas; and topographically it is more of a platform. So, discovering such a complex was a great surprise. Geographically, this is the southeasternmost paleoseismic dislocation within the Karelian part of the Fennoscandian Shield. Nothing of the kind can be encountered farther on, – explained Oleg Lavrov.
The characteristics of the bedrock disturbances has allowed for a preliminary inference of the magnitude of the seismic event. Such clefts and rockslides are clear signs of seismic events of fairly high intensity – no less than VIII on the MSK-64 scale.
The outcome of the seismic event
Scientists took a sediment core from a water body located within the presumed tectonic fault area, not far from the paleoseismic dislocation, and determined its age by radiocarbon dating. The dating suggests the sediments started accumulating ca. 11 350±230 calendar years BP. Hence, this seismic event could not have occurred before that. The earliest paleoseismic dislocations in Karelia known to date are 9 800–9 500 years old. If further research confirms the new dating, the postglacial earthquake in the Kubovo area will prove to be the most ancient in the region.
The geologists plan to continue research in the area to update the map of paleoseismic processes in Karelia.
«Closer research will help detect other types of tectonic disturbances. Although seismic activity in Karelia has been low, such studies are surely needed to obtain reliable data on seismicity manifestations in the region», – summarized the article authors.
– I’d like to acknowledge the initiative of local people and thank them. Not only did they notice the unusual natural feature, but they also reported it to scientists and then helped us organize the expedition. We value this greatly, – said Tatyana Shelekhova.
A fault in glacier-smoothed granitoid rock outcrops
This paleoseismic dislocation is not just of purely academic interest: scientists are convinced it deserves designation as a natural heritage site and can be turned into a touristic and educational destination. On top of its geological significance, the site boasts rare plant species, and archaeological artifacts have previously been discovered in the Vodla River valley. There are also some interesting hydrological features nearby, such as the Padun waterfall. There are traces of tectonic damage near it as well. However, as much as it is attractive, the site must be treated responsibly. To secure its conservation, researchers of multiple profiles are preparing papers for nominating it as a protected area.