Earthquake activity in Finland and the Russian North in December 1758: rare reports and their interpretation

Abstract

This investigation focuses on two historical earthquakes that occurred in the border region between Finland and Russian North in December 1758. They were close together in time and their magnitudes are among the largest observed in the region. We thoroughly searched for contemporary Russian and Scandinavian documentation on earthquake activity in several libraries in Moscow, Helsinki, Stockholm and Copenhagen. We found two primary reports, one from the Russian North and the other from Finland. The context and content of the reports indicate that they are independent and related to the dates of December 17 and December 31, 1758. The first occurrence was reportedly observed in Kandalaksha, Knyazhnaya Guba, Kovda, Chernaya reka and krest Vzista, and the second in Inari, Utsjoki, and Karasjok. We compiled macroseismic maps for both earthquakes and sets of possible parametric solutions that fit the sparse information available. We identified two types of uncertainty in epicenter and magnitude determination: one that stems from the ambiguity of intensity assessment at localities and the other from the spatial distribution of the data points. If no single solution is the best, we propose that all possible solutions be included in earthquake catalogs.