Springer Online Journal Archives 1860-2000
Summary The parameters and seismotectonics of an earthquake in the Baltic Shield, northern Finland, were studied. The instrumentally determined epicentre, 65.94°N, 27.21°E, falls in the intensity area ofI〈5. The results of the macroseismic study were: the area of perceptibility=6700 km2, maximum intensityI 0=5.25±0.05, focal depthh=10.0±0.5 km, absorption coefficient α=0.0035±0.0015 km−1 and magnitudeM m=4.0±0.1. The location of the focus was exact enough for seismotectonic study. The epicentre is located in the 0°-striking fractures and a parallel contact zone between granites and basement gneisses. On the other hand, it lies at the northern boundary (270–285°) of a tectonic block separated by fracture zones striking 270°, 285°, 330° and 30–40°. There have been seven known earthquakes in the area of the present study since 1891. Six of them occurred at the northern boundary of the block, of which five (including the Simojärvi earthquake of 1969) occurred within a period of three years. This block, with its deep (h=10 km) fractured boundaries, has been seen as a minor seismogenic unit and its northern boundary as the seismoactive part of this unit.
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