On a global scale the seismicity of Norway is, low-to-intermediate, even though it is the highest in north-western Europe. Available historical data indicates that an earthquake with size (magnitude on the Richter scale, M) 5 or larger occurs on the average every 10 years and one of M 6 or larger every 100 years. The largest earthquakes in historical times in Norway and surrounding offshore areas occurred in the Rana region in 1819, M 5.8, in the Vøring Basin in 1866, M 5.7, in the outer Oslofjord in 1904, M 5.4 and in the Viking Graben in 1927, M 5.3. The last earthquakes above M 5 include an M 5.3 event in the Vøring Basin in 1988, in an area with almost no earlier seismicity, and an M 5.2 event in the northeastern North Sea in 1989. This indicates that we could soon expect another larger earthquake in Norway, given that it is now almost 20 years since we had the last 10-year earthquake. However, earthquakes have usually little memory of past activity; therefore they occur quite irregularly even if their long-term occurrence is usually quite stable.
The seismicity of Norway is intraplate since it occurs far from any plate boundary, where the largest events occur. Even so Norway is a region with large variations in geologic conditions which also are causing earthquakes. The main structure that causes seismicity in this region is the continental margin (shelf) offshore Norway, where the seismicity is connected to large lateral variations in crustal structure across it. Moreover, some large offshore sedimentary basins (deposits) also attract seismicity. In the Nordland region there are also many earthquakes along the coast, similar to the west coast of Norway. Seismicity also occurs is in the old graben (rift) structures in the North Sea and in the Oslo region. Similar kinds of geologic structures are known globally to be responsible for fairly large earthquakes in intraplate areas, and some of these have even been above M 7. However, their return times at a given location are typically thousands of years, in contrast to decades or centuries at plate margins. Given that the largest historical earthquake in Norway is below M 6, it has therefore been suggested that there at present may be an earthquake deficit in this region.
Another potentially important factor for the seismicity of Norway is the fact that Fennoscandia has been fairly recently deglaciated, where we know that the initial and rapid uplift connected to this deglaciation resulted in a burst of larger earthquakes, possibly even triggering the giant Storegga slide about 8200 years ago. At present the postglacial uplift is probably only of marginal importance, however, since the present-day seismicity is considered to be more related to a number of other contemporary geologic processes.
The figure below is produced in cooperation between the Geological Survey of Norway (NGU) and NORSAR, and shows more than 200 years of earthquake locations plotted on top of topographic and bathymetric data. Some prominent postglacial faults are also indicated.
 Earthquake locations for the past 200 years.
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