Abstract
The results from regional seismic networks in the Baltic shield area are presented. About 200 earthquakes in the size ML=0.1–4.9 have been located and analysed. The fault plane solutions have been used for estimating the orientation of the regional deviatoric stress. The principal horizontal compression is oriented N60W. Strike-slip faulting on subvertical faults is the dominating mechanism. The existing fracture systems determine together with the regional stress field the type of faulting. The focal depths of the events indicate at least two different seismogenic layers: the upper crust down to 13–17km depth, and the middle crust 18–35km depth. At the depth range 18–28km the median size of the events is 0.7 magnitude units larger than at shallower or deeper depths. The Baltic shield earthquakes seem to be due to asperities in quietly sliding faults. The size of the slip may then be the most informative dynamic source parameter.
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Slunga, R.S. (1989). Focal Mechanisms and Crustal Stresses in the Baltic Shield. In: Earthquakes at North-Atlantic Passive Margins: Neotectonics and Postglacial Rebound. NATO ASI Series, vol 266. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-2311-9_15
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DOI: https://doi.org/10.1007/978-94-009-2311-9_15
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