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DDC:
550 - Earth sciences
Abstract:
On February 13, 1981, a relatively strong earthquake occurred in the Lake Vanern region in south-central Sweden. The shock had a magnitude of M"SUB L" = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 = or < M"SUB L" = or < 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg- wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5X10"SUP 20" resp. 4X10"SUP 18" dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.-Authors
