This study starts from the earthquakes of May 14, 1626 and June 22, 1626 as given in existing parametric catalogs for the Baltic (Fennoscandian) Shield. The first shock is located in North-western Russia, the second in Finland that belonged to Sweden at that time. A search for previously unknown Russian sources of information is performed, and secondary Swedish sources are replaced by primary ones. The contemporary sources are two Russian chronicles and two Swedish manuscripts. In addition, a later reminiscence is used. The contents of the sources are critically analyzed and augmented with background information. A new interpretation of one Swedish manuscript is presented. The earthquake dates are analyzed. A credible source of errors follows from the different calendars used. Macroseismic intensity assessment is possible for two places. A new solution of one earthquake felt in both territories is proposed. The available data are too fragmentary to prove it beyond doubt, but the scenario is feasible in many ways. Tentative earthquake parameters are calculated. Epicentral intensity is assessed at 6-7 (EMS), magnitude is estimated at 4.7-5.7. The epicenter is located in Russia close to the border between the two territories.

Archives and libraries were visited to find previously unknown documents testifying to the Lurøy, Norway, earthquake of 31 August 1819 in northernmost continental Europe. The focus here is on Sweden, Finland, and Russia, which are important for determining the area of perceptibility east of Norway. The new written sources include 12 notes or entries in original archived documents, six contemporary newspaper reports, and two recollections written down years later. The original documentation uncovered is contributory to establishing the authenticity of the observations in Finland and Sweden. The dates of the original documentation allow tracing of the dissemination of eyewitness accounts in writing from the inner area of perceptibility southward to the larger documentation and population centers. New sources of information include weather reports of the Royal Swedish Academy of Sciences, minutes of its meetings, and correspondence sent to the Senate in Finland. The minutes of meetings of the Academy indicate that ample data were collected in the Swedish province of Västerbotten. We found no original Russian documentation but uncovered national newspapers that are more reliable than the previously used Parisian newspaper. To increase transparency, we provide the first list of macroseismic data points (MDPs) including the respective documentation that testify to the Lurøy earthquake. A macroseismic intensity was assigned to a locality, using the European Macroseismic Scale of 1998, when adequate information was available. Accounting for the uncertainty of intensity assessment, the magnitude was estimated as moment magnitude M=5.9±0.2, reconfirming the ranking as the largest onshore or nearshore earthquake in the historical seismicity record of Fennoscandia. In addition to the reappraisal of the 31 August 1819 earthquake, a macroseismic map is provided for the earthquake of 17 February 1819, which was felt in northern Finland and Sweden. Some of its MDPs were previously associated with the Lurøy earthquake.

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Parameters for historical earthquakes have to be derived from written documentary materials. We argue that the steps involved can be approached through a defined theoretical framework using precise terminology. More pervasive use of the concept of ordinal variable is advocated when discussing earthquake intensity. The essential information available for parameter derivation consists of earthquake intensities and hierarchies between them as a function of space. To get error limits for earthquake parameters derived from sparse data, we propose to construct and illustrate possible earthquake occurrences of the past (so-called earthquake scenarios) that fit the available observations. Each possible scenario is associated with a probability, whose derivation involves expert judgment.

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