A joint Fennoscandian earthquake catalogue (FENCAT; updated after Ahjos and Uski, 1992) is an open-access catalogue providing all available non-instrumental and instrumental earthquake records in Fennoscandia and the adjacent offshore areas and it is compiled by Institute of Seismology, University of Helsinki, Finland. The catalogue covers earthquakes from 1467 to near present day. The original catalogue has been updated several times for different purposes. The published versions are called FENCAT(2014), FENCAT17, FENCAT(2021), FENCAT(20xx) and the number post text indicating the last year whose data are included in the dataset. FENCAT has been updated previously at the Institute of Seismology’s web sites and older versions have previously been called FENCAT catalogues without versioning. In the older version FENCAT(2014), data in the catalogue covers the area of 54°-75°N and 0°-45°E including Finland, Estonia, Latvia, Sweden, Norway, Denmark, and adjacent offshore areas, as well as parts of northern Lithuania and northwestern Russia. Because of the different degree of accuracy and homogeneity of the parameter data, the events were divided into historical (1375–1970) and instrumental (1971–) datasets. The source parameters for historical events are mainly macroseismic and for the instrumental data they are obtained by various iterative location procedures. The catalogue has been continuously updated with data from earthquake bulletins by the Institute of Seismology at the University of Helsinki (HEL), by the Department of Earth Science at the University of Bergen (BER), by the Department of Earth Sciences at the University of Uppsala (UPP), the Geological Survey of Denmark and Greenland (DNK) and since 2006 by the Geological Survey of Estonia (EST). The catalogue provides information about the time, location, depth, magnitudes, intensity and origin of data for the events. Since the beginning of year 2000, the catalogue lists the number of seismic stations included in the calculation of the location, the distance to the closest station, and the azimuthal gap of the stations, needed in the quality estimates of the location parameters. From 2009 onwards, all events that have less than four stations in their location solution are omitted from the catalogue. All versions of the catalogues published after FENCAT17 include information on the homogenized magnitudes of the earthquakes. The process of homogenization of the magnitudes is described in detail in an article under preparation by Uski et. al. (information will be updated later). The catalogue has been cleaned from explosions, induced and frost related events to the extent possible. In the old versions of the catalogue, up to FENCAT(2014), some events of questionable tectonic origin have been included with a special comment. From FENCAT17 onwards, those events have been removed. The removed data can, however, be requested from the Institute of Seismology, University of Helsinki. FENCAT(2021) is a version of FENCAT where years 2018-2021 were added and some further cleaning and updating has been done to the catalogue. Homogenized magnitudes are included in the catalogue. Using the CSV format has given the opportunity to rearrange data more comprehensively so the table now gives first information on time, location and depth of the events, then introduces mangitudes of the events, giving first homogenized magnitude, then seismic moment information and after that lists magnitudes from separate sources. After this there is macroseismic information and in the end different kinds of errors and comments. The FENCAT17 is a version of FENCAT made specifically for the Research Council of Finland’s project 337913 “Seismic Risk - Mitigation of induced seismic risk in urban environments” for calculating the seismic hazard for Finland and adjacent areas. Opening of the Nordic part of the data set has been partly funded through NordForsk grant 97318: “Nordic EPOS - A FAIR Nordic EPOS Data Hub”. The catalogue has been updated from the previous FENCAT(2014) for example by calculating homogenized magnitudes for the earthquakes. https://doi.org/10.23729/8fe15ab2-e805-447c-934e-21cb0463414b FENCAT(2014) is a subcatalogue of FENCAT that has been available through the website of the Institute of Seismology, University of Helsinki https://www.seismo.helsinki.fi/bulletin/list/catalog/Scandia_2014.html (site changed from 23.1.2025). References: T. Ahjos and M. Uski, 1992: Earthquakes in northern Europe in 1375-1989. Tectonophysics, 207, 1-23. J.K. Gardner and L. Knopoff, 1974. Is the sequence of earthquakes in Southern California, with aftershocks removed, Poissonian? Bull. Seism. Soc. Am. 64, 1363-1367.

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