ИСТИНА

Introducing the rigorous rules of historical seismology has definitely been a leap forward in comparison with the prevalent standards prior to the late 1970s. Instead of relying on earlier seismological compilations and forwarding their possible errors to new studies, priority is given to original and contemporary documentation of local and regional earthquake effects. Despite the advances, many regionally important earthquakes have not been re-appraised. On the one hand, a new investigation may not appear warranted, if competent, albeit old, studies exist. It can be complicated to argue convincingly how the potential improvements justify the invested time and effort. On the other hand, knowledge of past earthquake effects is needed for an understanding of the seismic histories of localities and for seismic hazard related to sites of engineering interest. This presentation attempts to conclude the ongoing re-appraisal of the Luroy earthquake of 31 August 1819. Its epicenter is located near Luroy, coast of Nordland, Norway. It is challenging to study by macroseismic means, because the region, northernmost Fennoscandia, was very sparsely populated, and there were only a few documentation centers located along the coasts. The previous two macroseismic maps were published in the 1980s and show that the earthquake had an exceptionally large area of perceptibility crossing country borders. It has been assigned magnitude Ms5.8, the largest in the historical seismicity record of the region. Basic research has been carried out in archives and libraries to uncover new and confirm old data points. Different types of revisions have been made: new data points have been found, existing ones removed because no report of any kind could be found to support them, and in-depth confirmation of localities with relatively ample or newly uncovered documentation. There is previously disregarded information about Stockholm, Sweden and Kola, Russia that are crucial for defining the radius of perceptibility and the macroseismic magnitude. Intensity assessment using the typically short descriptions available is uncertain; however, the approximate attenuation from Nordland to the outskirts of the area of perceptibility appears to be consistent.