Focal parameters of some Friuli earthquakes (1976-1979) using complete theoretical seismograms
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Vols. 1-18 (1924-1944), ISSN 0044-2801
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Abstract
The relocation of a number of large shocks and the estimation of their fault-plane dip, along with seismotectonic evidence, allow some conclusions about the mechanisms of Friuli (NE Italy) earthquakes. The largest shocks of the 1976 sequence are located in an area with an ESE-WNW trend, extending on both sides of the Tagliamento River. The May earthquakes occurred over the whole area, while the September aftershocks were concentrated in the centre of this area. The 1977-1979 events are spread over a wider zone. These shocks can be ascribed mainly to Dinaric structures. The hypocentre distribution of the largest 1976 events shows that the stress involved deeper crustal sectors in the south of this area (about 8 km) than in the northern part (where it does not exceed 6 km). The motion occurred either in the south along gently dipping planes, which probably correspond to the detachment surface between the post-Hercynian cover and the Paleozoic basement, or in the north along more steeply dipping planes (thrusts) within the Mesozoic cover, along with triggering and rearrangement in the shallower Alpine and/or Dinaric structures.
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