Neotectonic studies in the Ranafjorden area, northern Norway.

Abstract

The Ranafjorden area in northern Norway is a region of increased seismicity andanomalous land uplift. There is evidence for recent movements in the bedrock;1) A total of 0.89 m uplift of a bladder wrack mark from 1894 to 1990 inHemnesberget; 2) Anomalous low uplift of the islands of Hugla and Tomma in theouter Ranafjorden area (0,0 0.06 and 0.07 m from 1894 to 1990 compared to 0.25-0.30 m in the area to the north and the south); 3) Associated with the 1819magnitude 5.8-6.2 earthquake in the Ranafjorden area, an uplift of a shallowsea floor above sea level during an aftershock was reported in the bay Ut-skarpen. During the main earthquake a major land slide occurred at the samelocation. This earthquake is the largest North European near-shore earthquakerecorded in historical time; 4) An uplift of approximately 1 metre of a farm-house in the 1870's at Båsmoen. The observation has been made relative to thetwo neighbouring mountains Snøfjellet and Høgtuva. 5) Approximately 0.5 muplift of a boathouse in the bay Straumbotn during the last 50 years.There are, consequently, indications of recent faulting in the Ranafjorden areaIt is, however, difficult to find conclusive evidence for postglacial andpresent-day movements along specific faults. We have therefore establisheda Global Positioning System (GPS) network designed to measure the activegeological strain in the area.