SEISMODYNAMICS OF SWEDEN DEDUCED FROM EARTHQUAKE FOCAL MECHANISMS

Focal mechanisms from 18 major Swedish earthquakes, M(L)(UPP) greater than or equal to 3, reveal that: (1) several of the studied earthquakes have focal mechanisms with significant extensional stresses which fit well to the idea of postglacial rebound as an important stress generator, (2) in areas like south-western Sweden, the north-westerly trending compressional axes indicate that ridge push from the North Atlantic Ridge is also a considerable stress contributor; (3) some local tectonic features, like the Skalderviken depression in Kattegat, are momentous for seismotectonic interpretations. In addition to first P polarities, full waveform modelling for frequencies up to 3 Hz and epicentral distances up to 225 km provides rather robust focal-mechanism determinations. Focal depths of seven events, ranging from 11 to 37 km, are well resolved within a few km by waveform modelling.