A Reappraisal of the Lurøy, Norway, Earthquake of 31 August 1819

Abstract

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.

Testing the Environmental Seismic Intensity Scale on Data Derived from the Earthquakes of 1626, 1759, 1819, and 1904 in Fennoscandia, Northern Europe

“…The epicenter of the earthquake of 31 August 1819 is estimated to have been near Lurøy, along the coast of Nordland, in Norway (Figure 1), with the magnitude recorded as a moment magnitude of M5.9 ± 0.2, accounting for the uncertainty of the intensity assessment [29]. This reconfirms its ranking as the largest onshore or nearshore earthquake in the historical seismicity record of Fennoscandia.…”

“…In that respect, intense precipitation or snow melting shortly before a large earthquake may strongly reduce the stability of a slope, thus making it much more prone to failure when ground shaking occurs. For example, the 1819 Lurøy earthquake occurred after 3 weeks of rainfall [29], which likely affected slope stability during the earthquake. This precipitation effect poses an extra uncertainty in the assignment of ESI, which is especially pronounced in areas of high precipitation, such as western Norway.…”

“…The Lurøy earthquake triggered remarkable EEEs (Table 1), including liquefaction and widespread rockfalls as well as strong water turbulence in the fjords, indicating fierce ground shaking [12,18]. Our starting point was the updated list of intensity data points, which incorporates previously unknown written sources [29].…”

“…A list of EMS-98 intensity data points was readily available for the 1819 Lurøy earthquake [29]. In the list, data from some localities were combined so as not to base the intensity only on environmental effects, in accordance with the EMS-98 guidelines [11].…”