Earthquakes in northern Europe in 1375–1989

Abstract An updated version of the catalogue of earthquakes in northern Europe is presented. It comprises events inside a region window of about 55–80°N and 10°W–45°E, covering a 615-year period from 1375 to 1989. The data have been compiled using all the available historical publications, catalogues, studies and reports of the region, and for events from 1984 to 1989, a regional seismic parameter database maintained by the Institute of Seismology of the University of Helsinki. The number of events exceeds 5200, of which more than 40% have been registered since 1980. The huge increase of event reports is the result of the installation of new high-frequency networks for microearthquake studies and the upgrade of the seismic instrumentation. Because of the different degree of accuracy and homogeneity of the parameter data, the events were divided into historical (1375–1964) and instrumental (1965–1989) datasets. The source parameters are mainly macroseismic for historical events, and obtained by iterative location procedure for instrumental data. By assuming internal homogeneity between the different regional magnitude scales, we estimated the catalogue to be complete for events with magnitude ≥ 4.5 since the 1880's, magnitude 4.0–4.4 since the 1940's and magnitude 3.5–3.9 since the 1970's. Although the distribution of seismicity exhibits similar patterns in both datasets, the clustering of epicenters and offshore seismicity is more distinct in the instrumental period. The occurrence of the greatest events can be seen more clearly in the historical data. The earthquake epicenters are concentrated in the geologically younger tectonic provinces in the western part of the region and follow, with some exceptions, the tectonic fracture and fault zones. In the Fennoscandian area, 80% of the earthquakes occurred in the upper 20 km of the earth's crust. The deepest epicenters are in the southwestern corner of the region where the crust is thinnest.