Postglacial Faulting in Norway
Odleiv Olesen, Lars Olsen, Steven J. Gibbons, Bent Ole Ruud, Fredrik Høgaas, Tor Arne Johansen, Tormod Kværna
Abstract
The 90-km long Stuoragurra Fault Complex, part of the approximately 4–5-km wide Precambrian Mierojávri–Sværholt Shear Zone, constitutes the Norwegian part of the larger Lapland province of postglacial faults. It consists of three separate fault systems being 6–12 km apart. The faults dip 30–75° to the SE and can be traced to about 500 m depth. Deep seismic profiling shows that the shear zone dips at an angle of about 43° to the southeast and can be traced to about 3 km depth. A total of approximately 80 earthquakes were registered here between 1991 and 2019. Most of them occurred to the southeast of the fault scarps. The maximum moment magnitude was 4.0. The formation of postglacial faults in northern Fennoscandia has previously been associated with the deglaciation of the last inland ice. Dating of fault reactivation reveals, however, a late Holocene age (between around 700 and 4000 a BP). The reverse displacement of around 9 m and fault system lengths of 14 and 21 km of the two southernmost fault systems indicate a moment magnitude of about 7. The results from this study indicate that the expected maximum magnitude of future earthquakes in Fennoscandia is about 7.