Evidence of multiple slip events on postglacial faults in northern Fennoscandia

Abstract

An analysis of high-resolution LiDAR-based digital elevation models (DEMs), trenching of Quaternary deposits, diamond drilling and a structural analysis of the bedrock were conducted in order to characterise the geological structure and to derive full slip profiles of the Venejärvi–Jauhojärvi postglacial fault complex located in northern Finland. The Venejärvi-Jauhojärvi fault complex consists of 17 surface ruptures striking in a SW–NE direction, cutting through Late Weichselian till and traceable for a total distance of 29.9 km. Based on stratigraphical and structural analysis we show that the Naamivitikko fault segment, which is part of the Venejärvi–Jauhojärvi complex, hosted up to three distinct slip events and it is therefore argued that the prevailing single-rupture hypothesis of postglacial faults should be treated with caution. Based on the measured surface rupture dimensions, it is conservatively estimated that the maximum moment magnitude of the paleoseismic event that the complex hosted, ranged between Mw ≈ 5.8–8.4. If uncertainties in the scaling laws equating surface rupture dimensions to moment magnitudes are accounted for, a more realistic maximum moment magnitude range between Mw ≈ 5.8–7.6 is given.