Earthquake activity in F ennoscandia between 1497 and 1975 and intraplate tectonics

The systematic collection of macroseismic data on earthquake occurrence in Fennoscandia began in the 1880's when the use of questionnaires was initiated. Prior to that time the macroseismic information is fragmentary and incomplete, although the pioneering works of Keilhau (1836), Thomassen (1888), Kjellen (1903), Kolderup (1913) and others have preserved the essential data at least on the largest earthquakes. Using the pertinent macroseismic and seismograph data available, we have constructed seismicity maps for Fennoscandia covering the time interval 1497 to 1975. The earthquake activity is subdivided in 3 primary zones: the Western Norway, the Telemark-Vånem, and the Bothnian seismicity zones; and 3 secondary zones: the Lappland, the Norwegian Shelf, and the Norwegian Sea seismicity zones. The latter two zones are not part of Fennoscandia but were included to bridge the gap between the well-defined interplate seismic activity along the Mid-Atlantic Ridge and the relatively diffuse intraplate seismicity pattern of Scandinavia itself. The on-going tectonic processes causing the earthquakes are discussed in terms of plate driving forces and the geological history of Fennoscandia. There is in a number of areas, such as along the Bothnian coast of Sweden, some correlation between pertinent geological and geophysical information and observed seismicity, ev en though the possible causal connections are not quite clear.